KR100287306B1 - Integrated manufacturing method of crystalline fructose - Google Patents

Abstract

An integrated process is described for making both liquid sweeteners such as crystalline fructose and High Fructose Corn Syrup from a feed stream containing dextrose. A portion of the dextrose in the feed stream isomerizes to fructose and the detoxified / fractose stream that is read out is fractionated to produce a high fructose stream. A portion of the fructose in the high fructose stream is crystallized and the mother liquor remaining after crystallization is combined with the dextrose-containing stream to prepare a liquid sweetener.

Description

Integrated manufacturing method of crystalline fructose

FIG. 1 shows several steps in a conventional method for preparing 42% high fructose corn syrup (HFCS) and 55% HFCS (EFCS) from starch.

Figure 2 shows the starch-based integrated method for making both crystalline fructose and fructose-rich corn syrup (EFCS).

3 illustrates the method illustrated in FIG. 2 in more detail.

4 is a graph of massecuite temperature versus time after seeding for a typical variable supersaturated cooling program of the invention.

5 is a graph of temperature versus time in a batch crystallizer versus both a natural cooling curve (curve A) and a constant supersaturated cooling curve (curve B).

The present invention relates to an edible sugar. More specifically, the present invention relates to fructose obtained by isomerization of dextrose. The present invention also relates to a process for the simultaneous preparation of a syrup consisting of anhydrous crystalline fructose and essentially fructose and dextrose.

The present invention also relates to a method of crystallizing fructose by cooling the fructose solution such that the level of supersaturation differs during different periods of crystal growth and to produce a purified and concentrated fructose syrup.

[Liquid fructose product]

Fructose is a very valuable monosaccharide as a nutritional sweetener. The majority of fructose commercially available in the art is derived from corn starch and the main form of the product is High Fructose Corn Syrup (HFCS). Commercially available syrups contain 42 to 90% by weight of fructose on dry solids basis (dry solids basis; dsb) (in the following description, including the claims), "dsb" means "anhydrous solids." Weight in minutes ". The rest is mostly dextrose. HFCS, commonly used as a sucrose substitute in soft drinks, typically includes 55% fructose, 41% dextrose and 4% higher saccharides (all dsb%). The solids content of this syrup is usually about 77% by weight.

On an industrial scale, the preparation of HFCS is initiated using enzymatic liquefaction of purified starch slurry. The main source of raw material in the United States is corn starch obtained by the wet grinding process. However, it is possible to use starch with comparable purity from other sources.

In the first step of a typical process, the starch slurry is treated at high temperature to gelatinize. The gelatinized starch is then liquefied in two successive reactions and dextrinized with thermostable α-amylase. The product of this reaction is a soluble dextrin hydrolyzate with a dextrose equivalent (DE) of 6 to 15, suitable for subsequent saccharification steps.

Following liquefaction-dextrination, the rH and temperature of the hydrolyzate with DE of 10 to 15 are adjusted for the saccharification step. During glycosylation, the hydrolyzate is further hydrolyzed to dextrose due to the enzyme action of glucoamylase. Although saccharification can be performed as a batch reaction, continuous saccharification is carried out in modern manufacturing plants. In the continuous saccharification reaction, after adjusting the pH and temperature, glucoamylase is added to the hydrolyzate with DE of 10-15. The carbohydrate composition of a typical high dextrose saccharified solution is dextrose 94-96%, maltose 2-3%; Maltotriose 0.3 to 0.5; And high sugars of 1-2% (both dsb%). The product is typically 25 to 37% anhydride. This hydrolyzate having a high dextrose content is then purified to prepare a dextrose feedstock for the isomerization reaction.

Treated HFCS has very poor color and ash specifications, making it necessary to produce very good dextrose feedstock for isomerization. High purity feedstock is also essential for the efficient use of fixed isomerase enzyme columns.

Immobilized isomerase enzyme columns are used continuously over a period of months, during which a very large volume of dextrose feedstock passes through the column. Very low levels of impurities in the feedstock, such as ash, metal ions and / or proteins, can accumulate and reduce the productivity of the enzyme. For this reason, the dextrose feedstock is purified with a chromaticity of 0.1 (CRA x 100) and a conductivity of 5 to 10 micromho.

Carbonized, filtered and deionized high dextrose liquids are evaporated to a solid level suitable for isomerization. The feedstock is chemically treated by adding magnesium ions that not only activate immobilized isomerase but also competitively inhibit the action of residual calcium ions, a potent inhibitor of isomerase.

The isomerization reaction, which converts a portion of the dextrose to fructose, is usually carried out on a stream comprising from 94 to 96% dextrose (dsb) and high sugars 4 to 6% (dsb) in 40-50% anhydrous material. . The stream has a pH of 7.5 to 8.2 at 25 ° C. and is subjected to isomerase enzymatic action at 55 to 65 ° C. for 1/2 to 4 hours.

Converting glucose to fructose is a reversible reaction with an equilibrium constant of about 1.0 at 60 ° C. Thus, starting from a feedstock that continuously supplies 94-96% dextrose, it is expected that a fructose concentration of about 47-48% will be obtained at equilibrium. However, by the equilibrium point, the reaction rate of isomerization is too slow and the reaction must be terminated at a level of about 42% fructose conversion to achieve substantial reactor residence time.

In a given isocolum (fixed isomerase enzyme column), the conversion of dextrose (glucose) to fructose is proportional to the enzyme activity of the fixed isomerase. This activity is almost exponential and decreases with time. When the column is new and high in activity, the flow of feedstock through the column is relatively high because shorter residence times are required to achieve 42% fructose levels. As the service life of the column increases, the flow rate through the column must be proportionally reduced to prolong the residence time while replenishing the degraded activity to achieve a constant conversion level.

In practice, multiple isocolumns are used in parallel to minimize productivity variations associated with capacity and conversion levels. In this arrangement, each isocolum can operate essentially independently of one another. Changes in the total flow of isocolums must be kept within relatively narrow limits as evaporation and other processing operations are required. In practice, although the flow rate may not always be accurately adjusted at all times to yield 42% fructose stream, it is easy to achieve the flow rate on an average basis.

One of the most important operating variables in this process is the internal pH of the isocolum. The operating pH is usually intermediate between the maximum activity pH (typically about pH 8) and the maximum stability pH (typically pH 7.0 to 7.5). This is related to the fact that the dextrose feedstock is not pH stable at temperatures of about 60 ° C. Slight decomposition results in acid by-products, which lower the pH of the isocolum during operation.

Following isomerization, a typical preparation process uses secondary purification or polishing of 42% HFCS product. If the feedstock is held at a higher pH and temperature for a period of time, some additional color appears during the chemical treatment and isomerization process. The product also contains some additional ash from chemicals added for isomerization. This color and ash are removed by the second carbon and ion exchange system. The purified 42% HFCS is then evaporated typically to 71% solids for shipment.

It is generally known to use activated carbon to purify sugar syrups. U.S. Patent No. 1,979,781 (van Sherpenberg) mixes raw sugar syrup (i.e., not mixed with glucose syrup or invert sugar syrup) with 1-2 wt% activated carbon at 60 ° Brix (60% anhydrous solids) and for a short time While heating to 134 ° C. US Pat. No. 2,763,580 (Zabor) discloses a process for treating sugar liquids (e.g. sugar cane, beet or corn sugar) with a solids content of 10 to 60% by weight, in particular 20 to 56% by weight, at 125 to 200 ° F. It is widely described. This patent states that partial treatment can be carried out at certain concentrations or conditions, and then the treatment can be completed at higher concentrations (obtained by evaporation) or at other conditions.

Various patent documents relating to the preparation of fructose-containing corn syrups incidentally describe the carbonization and subsequent concentration of aqueous solutions with varying fructose concentrations (dsb) and varying anhydrous solids levels. Scarlet et al., US Pat. No. 3,383,245 and Katz et al., Pat. No. 3,690,948, disclose a fructose-containing syrup having about 20% (dsb) fructose as about 40% anhydrous solids. After treatment, a method is described in which the syrup is subsequently concentrated by evaporation, for example, to 70-83% dry solids.

Katz et al., US Pat. No. 3,684,574, discloses a method of carburizing a syrup containing about 20% (dsb) fructose as a low anhydrous solid of 20% and subsequently concentrating the syrup. It is describing. US Pat. No. 4,395,292 to K3tz et al, introduces a carbonized mixture of fructose and dexrose having anhydrous solids of 10 to 70%, preferably 40%, into a fractionation column and extracts the fructose-containing extract. It describes how to concentrate. US Pat. No. 4,395,292 provides examples in which extracts containing at least 90% of fructose can be obtained, and fractional separation of 40% anhydrous solids source results in fractions having 100% (dsb) fructose as 9% anhydrous solids. (Example 7) is described.

HFCS products from the isomerization reaction typically contain 42% fructose, 52% unconverted dextrose and about 6% oligosaccharides. For the reasons discussed above, these products exhibit a substantial maximum level of fructose that can be achieved by isomerization. In order to obtain products with higher levels of fructose, fructose must be selectively concentrated. Many conventional separation techniques cannot be applied for this purpose because these techniques cannot readily separate two isomers having essentially the same molecular size. However, fructose preferentially forms complexes with other cations such as calcium. This difference has been used to develop industrial separation processes.

Basically, there are two different industrial methods currently used for large scale fructose purification. In both cases, the resin in the preferred cationic form is used in a packed bed system. One method uses inorganic resins that induce selective molecular uptake of fructose. See R.J. Jensen, "The Sarex Process for the Fractionat ion of High Fructose Corn Syrup," Abstracts of the Institute of Chemical Engineers, 85th National Meeting, Philadelphia, Pa., 1978.

Chromatographic fractionation using organic resins is the basis of a second industrial separation method [K. Venkatasubramanian, "Integration of Large Scale Product ion and Puri fication of Biomolecules," Enzyme Engineering, 6: 37-43, 1982 ]. When an aqueous solution of dextrose and fructose (eg 42% HFCS) is fed to the fractionation column, fructose is retained in the resin to a greater extent than dextrose. Deionized and deoxygenated water is used as eluent. Typically, the separation takes place in a column packed with a low crosslinked, fine mesh mesh of polystyrene sulfonate cation exchange resin, using calcium as the preferred salt form. Concentrated products containing about 90% fructose are named Very Enriched Fructose Corn Syrup (VEFCS). This VEFCS fraction can yield a product having a fructose content of 42% to 90% for blending with 42% HFCS feed material. The most typical of these products is 55% rich fructose corn syrup, which is sometimes referred to as EFCS or 55 EFCS. Katz et al., US Pat. No. 4,395,292, fractionally separates a mixture of fructose and dextrose into various fractions and combines the fructose-rich fractions to produce a syrup containing 55.8% (dsb) fructose. An embodiment (Example 1) to be described is described. This example also describes a single fraction having a high concentration (dsb) of fructose (eg 75.1% (dsb)) and fractions containing lower concentrations of fructose [eg 58.2% (dsb) fructose. Tods and 64.5%, (dsb) fructose].

Treatment of other raffinate streams in a fractional separation process is an important concern. In general, the dextrose rich raffinate stream is recycled to the dextrose feed of the isocolumn system for further conversion to 42% HFCS. Raffinate streams having higher levels of fructose than feed stream and containing dextrose and fructose can be recycled through a fractionation separator to reduce water use while maintaining high solids levels. Raffinate streams rich in oligosaccharides can be recycled to the saccharification system.

Since water is used as the elution medium, this has a significant impact on the overall evaporative load on the system. Very low solids concentrations increase the risk for microbial contamination in the system. Thus, the most important design parameter that represents the overall process economics is to maximize solids yield at acceptable purity while minimizing the dilution effect of eluent cleaning. For optimum yields, the efficiency of feed and water use should be maximized. Yields are important in reducing the cost of reisomerization.

Processes used to achieve these goals include recycling techniques, higher leveling of dendritic phase with proper redistribution in packed columns, and introduction of multiple inlet and outlet points in the column. This method can be used to increase purity and yield.

In a batch fractionation system, a slight obvious increase in the purity of the feed to the fractionation column, i.e. higher fructose levels, increases the yield at the desired product purity, resulting in much higher yields in preparation. In practice, this means maximizing the ratio of the volume of sugar introduced per resin volume per cycle, minimizing the ratio of the required water column per resin volume per cycle, and careful flow distribution to the column.

[Solid Fructose Product]

Many methods for crystallizing fructose are known. Crystalline fructose can be prepared, for example, by adding anhydrous alcohol to the syrup obtained by acid hydrolysis of inulin. Bates et al., Natl Bur Std. Circ. C 4 O, 399, 1942]. The preparation of fructose from dextrose is described in US Pat. No. 2,354,664 and US Pat. No. 2,729,587 describes the preparation of fructose from sucrose by enzymatic conversion.

Fructose forms orthorhombic, bisphenoidal prisms from alcohols that decompose at about 103-105 ° C. Hemihydrates and hydrate crystalline forms are also known, but it is desirable to avoid this class of forms because they are substantially hygroscopic than the anhydrous form and the melting point is close to room temperature. Due to this property, such crystalline fructose is very difficult to handle.

Solvent Crystalline Fructose (SCF) is prepared by mixing an organic solvent, such as modified ethyl alcohol, with a high fructose stream (95% dsb). The stream is cooled to crystallize and pure crystalline fructose. To form. The product is centrifuged to separate from the mother liquor, desolvated and dried.

U.S. Patent 4,199,374 describes a method of making an SCF. Fructose is crystallized from a solution of VEFCS in ethanol. The solution is seeded using fine crystals of fructose or glucose. The crystals are collected by filtration, centrifugation or other suitable method. These crystals are then washed with alcohol and dried under vacuum. In order to obtain free-flowing microcrystals of fructose, the water content of alcohols and syrups must be carefully controlled.

Dried fructose sweeteners (DFS) can also be prepared simply. In the DFS process, a high fructose stream derived from fractional separation is dried in a rotary dryer and then sized in a sorter comprising a screen and a mill. US Pat. No. 4,517,021 describes the preparation of fructose solids of the above semi-crystalline granules comprising less than about 2% by weight of water. This patent describes that about 60% by weight of the product is crystalline fructose and less than about 35% by weight is amorphous fructose. A drum dryer with air having an initial temperature of 50 to 80 ° C. is used. Part of the solid fructose product can be recycled as crystallization initiator.

One disadvantage of the DFS process is that it is not pure fructose because the product is a whole sugar product and does not meet the Food Chemicals Codex criteria for "fructose". Moreover, since the product is not completely crystalline, the hygroscopicity is greater, and therefore handling is more difficult under conditions moist than crystalline fructose.

An aqueous process can also be used to produce crystalline fructose. The aqueous crystalline fructose process is typically initiated with a high content of fructose feed stream, in which the fructose is crystallized from the solution. A number of references describe this process.

In US Pat. No. 3,513,023 crystalline anhydrous fructose is obtained from an aqueous solution of fructose (minimum 95% ds). The pH of this solution should be between 3.5 and 8.0. The fructose solution is concentrated in vacuo until the moisture content reaches 2-5%. The solution is cooled to 60-85 ° C. and seeded crystalline fructose and stirred vigorously while maintaining the temperature at 60-85 ° C. The patentees describe that the crystalline mass can be slowly cooled and then pulverized or polished and subsequently dried to produce a non-viscous free flowing microcrystalline powder. This method is said to avoid the formation of predominantly glassy products when this type of fructose solution is concentrated in vacuo and left to cool in a conventional manner.

In US Pat. No. 3,883,365, fructose is crystallized from 90% ds of fructose / glucose aqueous solution containing 90-99% (dsb) fructose. The solution is saturated (58-65 ° C.). Fructose is crystallized from solution by adding a uniform size of fructose crystals. The formation of new crystals is minimized by keeping the distances of the seed crystals close to each other and maintaining the supersaturation between 1.1 and 1.2. As crystallization proceeds, the volume of the solution increases continuously or stepwise. The optimal pH of the fructose solution is referred to as 5.0. The average crystal size of the crystals thus obtained is 200 to 600 microns. Centrifugation is used to separate the crystals from the solution.

US Pat. No. 3,928,062 describes a method for obtaining anhydrous fructose crystals by seeding a solution comprising 83 to 95.5% (based on anhydride) total sugars containing 88 to 99% fructose. Crystallization can be accomplished by simply cooling the solution under atmospheric pressure or by evaporating water under reduced pressure. Hemihydrate and dehydrate formation is avoided by performing crystallization within a certain range of fructose concentrations and temperatures. This range is within the supersaturation range before the point at which the hemihydrate begins to crystallize. It is mentioned that the mother liquor can be used repeatedly for the crystallization of further yields in the same manner as the first yield without further treatment. The addition of seed crystals can be achieved by using a massecuite form prepared in advance by suspending the crystals in the fructose solution.

In US Pat. No. 4,199,373, fructose syrup (88-96% dsb) is seeded with 2-15% by weight of fructose seed crystals and the seeded syrup is left at about 50-90 ° F. of relative humidity of 70% or less. Crystalline fructose is prepared. Crystallization is said to require 2 to 72 hours. The crystalline product produced in this way is in the form of huge pellets.

US Pat. No. 4,164,429 describes a method and apparatus for making crystallized seeds. A series of centrifuge devices are used to select seed crystals that fall within a predetermined range of sizes from the seeded solution.

Crystallization Cooling Curve

Methods of cooling saturated or supersaturated solutions to crystallize the material are of course generally known.

In addition, natural cooling of saturated or supersaturated solutions often leads to severe nucleation, which is known to have a wide range of particle size distributions that are undesirable for crystalline products. See, eg, Encyclopedia of Chemical Technology, Vol. 7, pp. 243-285 (Kirk-Othmer, Ed. John Wiley & Sons, NY, 3rd ed., 1979) discusses crystallization, and natural cooling produces supersaturated peaks early in the cooling period, causing excessive nucleation. Let's do it. This document teaches that a constant level of supersaturation can be maintained by subsequent controlled cooling curves, thereby allowing control of nucleation within acceptable limits. 5 reproduces the natural and controlled cooling curves known in the literature.

Various aspects of the invention are briefly described below.

[I. Integrated Manufacturing Method of Multiple Fructose Sweeteners]

In one aspect, the present invention is broadly directed to an integrated process for the preparation of multiple sweeteners containing fructose.

[A. Simultaneous Preparation of Liquid Sweetener and Crystalline Fructose]

In certain embodiments, the present invention comprises the steps of crystallizing fructose in an aqueous solution of fructose to produce a mixture comprising crystalline fructose and a mother liquor; Separating crystalline fructose from the mother liquor; And preparing a liquid sweetener comprising dextrose and fructose by mixing dextrose with a mother liquor, and a method of preparing a liquid sweetener comprising crystalline fructose and fructose and dextrose. .

When preparing crystalline fructose from an aqueous solution, it is common practice to repeatedly and continuously strike crystals in order to concentrate impurities in the mother liquor, referred to as molasses. Such molasses is generally so rich in impurities that it is only valuable as an animal feed supplement or fermentation medium. US Pat. No. 3,928,062 teaches that the mother liquor from fructose crystallization can be used repeatedly to crystallize additional yields of fructose crystals. The difficulties associated with isomerizing and fractionating corn syrup to obtain a crystallization feed having a high concentration of fructose and the relatively low yield of fructose crystals from a single strike of crystals using conventional crystallization techniques are Continuous strike of the tods crystals makes the mother liquor appear to be recycled. However, by adding dextrose to the mother liquor, integrating liquid sweetener and crystalline fructose yields two good quality sweeteners. This, in turn, can maximize the yield of fructose useful as a sweetener, which justifies the difficulty of isomerization. However, this method of dextrose is applied to the mother liquor because the overall aspect of fractional separation is to remove dextrose to produce a crystallization feed. The addition of implies the loss of the product obtained in the fractionation separation in that part of the yield obtained through the fractionation separation is lost.

In certain embodiments of this aspect of the invention, the invention comprises isomerizing a portion of dextrose in a feed stream to produce a first dextrose / fructose stream comprising dextrose and fructose; Separating the first dextrose / fructose stream into a first feed stream and a second feed stream; Fractionally separating the first feed stream to produce a high fructose stream; Crystallizing the fructose in the high fructose stream to produce a mixture comprising crystalline fructose and mother liquor; Separating crystalline fructose from the mother liquor; And blending at least a portion of the mother liquor with a second feed stream to produce a second dextrose / fructose stream having a higher ratio of fructose to dextrose than the first dextrose / fructose. A process for preparing crystalline fructose and streams comprising dextrose and fructose from a feed stream comprising troze (including the terms "dextrose, fructose" Stream means a stream comprising dextrose and fructose ").

In a related aspect, the invention comprises the steps of crystallizing fructose in an aqueous solution of fructose to produce a mixture comprising crystalline fructose and mother liquor; Separating crystalline fructose from the mother liquor; A method of preparing a liquid sweetener comprising crystalline fructose and fructose, comprising the step of preparing further liquid sweetener comprising fructose by inhibiting further crystallization in the mother liquor.

The mother liquor remaining after crystallization is a saturated solution of fructose. Prior art, such as US Pat. No. 3,928,062, teaches that the mother liquor can be used repeatedly for crystallization of further obtained crystals. In order to produce an additional yield of crystals, the saturated mother liquor must be heated and concentrated to obtain a suitably supersaturated fructose solution, which allows crystallization in the mother liquor. Rather than being able to crystallize additional yields, it has been found to be advantageous to inhibit further crystallization so that the mother liquor can be used in the preparation of liquid sweeteners. As mentioned above, the mother liquor is a saturated solution of fructose. In order to prevent precipitation of the fructose crystals during handling, transportation and / or storage, steps must be performed to inhibit crystallization of fructose in the mother liquor. This aspect of the invention relates to the first aspect of the invention mentioned above in that further crystallization should be avoided. However, this embodiment does not necessarily require a loss of fractional separation yield, since inhibiting further crystallization does not necessarily require the addition of dextrose, i.e. simply diluting the mother liquor with water This is because crystallization can be suppressed without diluting the fructose purity of the mother liquor based on anhydrous solids.

[Separated Separation of Many High Concentration Fructose Sweeteners]

In a related aspect, the present invention relates to a feed stream comprising dextrose and fructose comprising dextrose-rich raffinate, low fructose extract and high fructose extract, wherein the high fructose extract is about 90% (dsb) Fractional separation); And mixing the low fructose extract with a dextrose composition comprising a higher concentration (dsb) of dextrose to produce a liquid sweetener, wherein one or more of the fructose sweeteners comprises It comprises a process for the production of) (including the rose and fructose).

In the present invention, "fructose sweetener" includes all sweeteners containing fructose, regardless of whether the fructose is amorphous or crystalline dispersed in solution. For example, high fructose extracts can be used to prepare syrups containing fructose, crystalline fructose or semicrystalline fructose, where at least some of the fructose is in an amorphous solid phase.

Separation of isomerized dextrose syrups (ie, containing both fructose and dextrose) to produce fructose sweeteners comprises dextrose raffinate and fructose extracts and residual fractional separation products. It is usually done by recycling together. For example, US Pat. No. 4,395,292 states that such operating conditions are desirable. However, by applying two extracts, one with a high concentration (dsb) of fructose (ie, a high fructose extract) and the other with a low concentration (dsb) of fructose, the degree of aggregation degradation of the isomerized feed And all related problems (e.g. unfavorable pressure drop due to reduced fractionation capacity, higher evaporation from increased effluent and / or higher effluent flow rate required to increase decomposition). A higher concentration of fructose extract can be obtained than a single extract.

The use of low fructose extracts is narrower than that of high fructose extracts (ie, using low fructose extracts to produce crystalline fructose is difficult), but fructose in low fructose extracts Can be used to increase the fructose content of syrups containing much less fructose, for example by mixing it with isomerized corn syrup (eg 42% fructose corn syrup). 55% fructose corn syrup).

In a particularly preferred embodiment of the present invention, a high fructose extract is used to prepare a crystallizer feed for fructose crystallization.

Thus, in one aspect, the present invention comprises the steps of: separating a stream comprising dextrose and fructose into dextrose-rich raffinate, low fructose extract and high fructose extract; Crystallizing fructose from an aqueous solution derived from the high fructose extract; And mixing the low fructose extract with a dextrose composition having a higher concentration (dsb) of dextrose to produce a liquid sweetener comprising dextrose and fructose. The present invention relates to a method for preparing a liquid sweetener comprising dextrose and fructose.

Such an embodiment would be impractical to separate the dextrose / fructose feed stream from the isomerization process to produce a single extract because the fructose concentration (dsb) normally required to crystallize fructose from an aqueous solution is too high. It is particularly advantageous because it can. In other words, such degradation is impractical because the resolution needed to prepare a single extract with sufficiently high fructose purity useful as a crystallizer feed often reduces the fractional separation capacity and / or increases other difficulties associated with fractional separation. .

A possible disadvantage in applying both high fructose and low fructose extracts and using them separately to produce crystalline sweeteners and liquid sweeteners respectively is that low fructose that can be used to increase the fructose content of isomerized corn syrups The amount of fructose in the tods extract is less than the amount available in a single fructose applied with the same aggregate decomposition of degradation. Thus, the total amount of fructose (dsb) that can be used as a liquid sweetener is reduced. This drawback is ameliorated by crystallizing some of the fructose in the high fructose extract to make the mother liquor available. In other words, in a particularly preferred embodiment, a liquid sweetener (such as 55% fructose corn syrup) is prepared by mixing fructose-containing mother liquor, low fructose extract and isomerized corn syrup.

[II. Variable supersaturation cooling curve]

In another aspect, the present invention provides a method comprising the steps of: cooling a solution comprising fructose through an initial temperature range at an initial cooling rate; Cooling the solution through an intermediate temperature range at an intermediate rate slower than the initial rate; And cooling said solution through the final temperature range at a final rate faster than the intermediate rate. The method relates to a method for preparing crystalline fructose from a solution comprising fructose.

5 shows a typical cooling curve used in the crystallization processes. Curve A is a natural cooling curve and curve B is a controlled curve designed to reach some level of supersaturation. 4 shows the variable saturation cooling curve of the present invention. Comparing the two figures it can be seen that the conventional curve and the curve of the present invention are completely different.

Using a cooling rate in the intermediate cooling period that is slower than the cooling rate in the initial and final periods minimizes both spontaneous nucleation in the solution and thermally induced decomposition of fructose in the solution, especially during the initial cooling period. Reduced nucleation results in a nearly uniform particle size distribution of crystal products, reduced heat damage, increased yields of fructose crystals and mother liquor, and reduced levels of impurities, which are decomposition products in the mother liquor, resulting in a source of fructose for liquid sweeteners. Its usefulness as is enhanced.

[III. Method for Purification of High Fructose Syrup by Carbon Treatment at Low Solids Content]

In another aspect, the present invention provides a method for producing a fructose solution having a fructose concentration of greater than about 75 (dsb) weight percent and anhydrous solids concentration of less than 40 weight percent; Contacting the solution with activated carbon to prepare a purification solution of fructose; And evaporating the purification solution to anhydrous solids at a concentration exceeding 40%.

In order to purify sugar syrups, it is generally known to treat sugar syrups with activated charcoal, but to reduce the availability of fructose in the syrup and to inhibit the crystallization of fructose from the syrup and / or of syrup or sweeteners prepared therefrom. If activated carbon is present to reduce the formation of by-products (eg, difructose) that can affect organoleptic properties, fructose syrups having a high concentration of fructose (dsb) should have a relatively low solids concentration Turned out to be. Tables II and III show the effect of solids concentration on difructose formation in high concentrations of fructose (95 +% dsb) syrup over time upon contact with activated carbon.

In a related aspect, the present invention also provides a method for preparing a high fructose stream having fructose greater than 90% (dsb) by fractionally separating a stream comprising dextrose and fructose; Contacting the high fructose stream with activated carbon to produce a purified fructose stream; Evaporating the purified fructose stream to produce a fructose solution; And it relates to a method for producing crystalline fructose, comprising the step of crystallizing fructose in the aqueous solution of fructose.

The sequence of contacting and then evaporating the high fructose stream ensures that the contact is carried out at a relatively low solids concentration since the solids concentration of the high fructose extract is typically low upon elution from the fractionation column.

In another related aspect, the present invention provides a method of preparing a mixture comprising crystallizing fructose in a fructose solution to produce a mixture comprising crystalline fructose and a mother liquor containing fructose; Separating crystalline fructose from the mother liquor; Mixing at least a portion of the fructose in the mother liquor with a liquid comprising water to form a fructose solution having a low solids content (eg, less than about 70% anhydrous solids); Contacting the fructose solution with low solids content with activated carbon; And evaporating the fructose solution having a low solid content to form a fructose solution having a high solid content.

In a particularly preferred embodiment, the mother liquor resulting from the crystallization of fructose is treated with activated carbon by mixing with a liquid comprising water (e.g. tap water, sweet water, saccharide syrup such as 42% fructose corn syrup, etc.) Thereby reducing the solids content before evaporating to a higher solids content. The high solids solution obtained can be used in a variety of ways, for example in crystallizer feeds, high fructose corn syrup sweeteners or in the production stream therefor, all of which are treated with activated charcoal and then Prior to evaporation, the solid concentration of the mother liquor is reduced to provide the accompanying advantages as mentioned above.

An important feature of the present invention lies in the synergy obtained when anhydrous crystalline fructose (ACF) is prepared with EFCS. The yield of fructose crystals from fructose bags is typically at the level of 40 to 55% (eg 45%). Longer crystallization times can increase yield, but can reduce process throughput. Thus, significant advantages are obtained by integrating the fructose crystallization method with the method that not only provides the fructose food from the ACF crystallization method but also can accept amorphous fructose from the ACF process without any loss.

In some crystalline fructose processes of the prior art, the amorphous portion is recycled through the crystallization process. The problem with this method is that since crystallization is essentially selective for fructose, undesirable byproducts such as difructose, 5- (hydroxymethyl) -2-furfural (HMF) and high sugars accumulate in the recycle stream. Tends to be. As a result, the recycle stream eventually becomes too contaminated with by-products and has to purge the contaminants from the system, resulting in substantial loss of fructose.

The present invention solves the problem of increased by-product accumulation by introducing a solution material (mother liquor) remaining after fructose crystallization into a process for producing a high fructose liquid sweetener. In this aspect, undesired by-products are not concentrated during the stage of the integrated process to produce ACF, but rather are removed continuously from this system. This consolidation method eliminates the need for fructose-containing purging streams, allowing the fructose to be preserved in more economically valuable products.

Referring to FIG. 1, it can be seen that the preparation of 55% HFCS (EFCS) requires a separation (fractional separation) step in the process stream. Generally, fractional separation is required to produce syrups with a fructose content of greater than about 48%. For the purpose of crystallizing fructose, syrups containing at least 95% of fructose (dEb) are preferred. It is possible to crystallize fructose from a solution containing less fructose, but the yield is low and this method is economically undesirable.

Fractional separation techniques are known that provide a 95 +% fructose stream from a feed comprising about 42% (dsb) fructose (typical yield from dextrose isomerization). Thus, an ACF feed stream can be obtained from an EFCS process with no or slight modifications. More preferably, the fractionation system is one of the simulated mobile total chromatography types, as is well known in the art.

Referring now to FIG. 2, the integration process is described in detail. As indicated by the block labeled “first conversion / purification”, the starch is first converted to dextrose using the conventional enzyme based process mentioned above.

[Isomerization]

The isomerization step uses an enzyme that converts dextrose to fructose. The enzyme is immobilized on the carrier and, if consumed, immobilized on the column (isocolum) until replaced. One advantage of the present invention is the efficient use of increased amounts of isomerase in isocolumns. Due to the periodic fluctuations in demand for EFCS (55% fructose), producers who invest in additional isomerase to meet maximum demand can increase the isomerase capacity even when the production of EFCS is relatively low. You must pay for the level throughout the year. By selectively implementing the integration process described herein, producers can apply more high fructose streams from fractional separation trains to EFCS production when product demand is high, and when there is less demand for EFCS. By using a much larger portion of the stream in the production of ACF, increased levels of isomerase can be efficiently utilized. In this way, investment in increased isomerase dose can be made efficiently throughout the year.

[Separation Separation]

Fractional separation occurs in a group of vessels containing trains or resins, which operate in the order of separating fructose from dextrose in the syrup feed stream. The feed stream and the eluent stream are fed to the train and one or more high fructose product streams, high dextrose raffinate streams and / or one or more high oligosaccharide raffinate streams are removed. As shown in FIG. 3, the high dextrose stream is recycled to the isomerization reaction to convert to fructose, while the high fructose stream (s) are run or blended into the ACF portion of the process to produce EFCS. do.

Fractional separation capacity is determined by feed flow rate, percent fructose in the product stream and fructose recovery in the stream. For a given fructose content (dSb), the higher the fractionation capacity, the lower the fructose conversion required for isomerization. Thus, in order to further lower the cost of the isomerase component, fractional separation is preferably operated continuously at its maximum capacity.

In order to obtain substantial crystallizer yield from the ACF process, the fractionated separation product should have a fructose greater than about 90% (dsb) and preferably greater than 95% (dsb) of fructose. Since this is higher than the 90% (dsb) fructose that is typically separated in an EFCS process, fractional separation capacity can be reduced only by using special operating conditions for a conventional fractionation system. The operating conditions are 1) lowering the syrup feed rate without increasing the elution rate to increase degradation and / or (2) increasing the elution rate to increase decomposition. These operating conditions have the disadvantage that product emissions must be reduced and / or added water to be removed continuously, thereby at least additional energy is consumed. However, another preferred method exists.

As will be apparent to those skilled in the art, two types of at least partial decomposition occur when an aqueous solution comprising dextrose and fructose is passed through a suitable chromatographic column. In order to achieve fractional separation, the eluate from the column must be properly converted in order to separate the desired fractions. The converted part is generally referred to as a "cut". A "narrow cut" contains much less volume of eluate components than a "wide cut." In other words, in terms of purity, it is possible to optimize separation for a particular type by appropriately accepting narrow cuts. The general exchange to accommodate narrow cuts from the eluate adversely affects the total recovery of the selected type.

A 95 +% (dsb) fructose stream, which is preferred as a feed to the crystalline fructose portion of the process described above, can be obtained by suitably accepting narrow cuts from the product stream of the fractionation system of a conventional process conventional for the production of EFCS. Turned out to be. One particularly preferred fractional separation system is John F .. US Patent No. 861,026, filed August 5, 1986, titled Simulated Moving Bed Chromatographic Separation Apparatus, owned by John F. Rasche. The teachings of this document are incorporated herein by reference.

When using the fractional separation system of the present invention, a preferred method of operating the above-mentioned chromatographic separation apparatus is to increase the eluent to feed ratio from about 1.7 to about 2.0. This syrup feed is preferably about 60% by weight of anhydrous material and is maintained at a temperature of about 140 ° F.

The raffinate stream from the fractionation separation system can be distributed in a manner similar to that used to nourish the extract stream. In this process, the streams relatively rich in oligosaccharides can be separated for recycling to the saccharification system, transferred to a separator, used in the saccharification system or purged from the system.

In the absence of purging or recycling of oligosaccharides to the saccharification system, only the output from the system for oligosaccharides becomes the extract stream, unless typical isomerization affects oligosaccharides. That is, the oligosaccharides in the raffinate stream recycled to the isomerization system are simply passed through the system and returned to the feed to the fractionation separation system without being changed.

Since at least a portion of the extract stream is used as a feed to the fructose crystallization portion of the process, the presence of oligosaccharides in the extract stream is undesirable and crystallization of fructose is achieved from a solution containing a minimum amount of other species. Is preferred. Similarly, oligosaccharides are undesirable in liquid sweeteners prepared by the process of the present invention, so only a limited amount of the oligosaccharides can be removed from the system via the liquid product.

Another advantage lies in recycling the oligosaccharide-rich stream from the fractionation system to the saccharification system. Such streams will typically have a relatively low anhydrous content, most typically about 10% d.s. (ie, this corresponds to about 90% by weight of water). Starch slurries obtained from the liquefaction / dextrinated portion of this process typically must be diluted prior to saccharification. The water in the oligosaccharide stream can be replaced by at least a portion of the water used as diluent for the starch slurry, thereby conserving water and reducing the evaporation capacity required for the system as a whole.

[Blend]

In a conventional EFCS process, the high fructose extract from fractional separation is blended with the isomerization product (typically containing 42-48% (dsb) fructose) to produce the desired fructose content in the final product [55 for EFCS]. % (dsb)] is obtained. In the integrated process of the present invention, obtained from the centrifugation step of the crystallization process containing from about 88% to 92% (dsb) fructose, preferably from 90% to 92% (dsb) fructose, at approximately 83% ds. Mother liquor is also useful for blending. This blending adds additional flexibility to the process as the blend can typically be ion exchanged, carbonized and then introduced into an EFCS polishing step that is evaporated to 77% ds as part of a typical EFCS preparation. Grant. (-) In FIG. 3 represents an option for blending. Optimal selection of the blend stream is of course dependent on the mass balance of the system as a whole.

The ACF process does not add chemicals to the high fructose stream, except for very small amounts of hydrochloric acid or soda ash for pH adjustment, so that no significant traces of new traces are produced during the ACF process. Color bodies, HMF and difructose may be produced during the evaporation step of carbonization and crystallizer feed treatment. However, these compounds can be removed by the final carbon treatment and ion exchange treatment during the EFCS process.

This is not a major problem as most of the steps of the whole fructose process can be operated at the high anhydrous level as microbial growth is inhibited. As a result, acetaldehyde levels should not be significantly increased, which in some cases can be reduced by the final ion exchange and final evaporation steps.

Fructose Feed for Crystallizers

[pH adjustment]

The pH of the aqueous solution of fructose from which the fructose crystals are obtained is found to be about 3.7 to about 4.3, although there is also a reverse teaching (see US Pat. No. 3,883,365). Proper adjustment of the fructose feed pH for the crystallizer is necessary to minimize the formation of difructose anhydride. The presence of difructose anhydride in the crystallizer was found to adversely affect the size distribution of the fructose crystals formed, lowering the yield of the crystallizer. Anhydride formation is believed to be minimal when the pH range is 3.7 to 4.3. Higher anhydride formation rates are obtained in the upper and lower regions of this range. It is also believed that color formers are favorably formed at high pH levels.

EXAMPLE

The effect of pH on the generation of impurities in syrups containing approximately 95% of fructose based on the solubility of fructose and anhydrous solids is investigated as described below. The syrups investigated are representative of those used as feed to the fructose crystallization portion of the described process.

Crystalline fructose is added to a sample of VEFCS (90% fructose, dsb) to make a syrup comprising approximately 95% (dsb) of fructose. This syrup is then treated using activated carbon granules, as described herein under the subheading "Carbon Treatment". That is, this syrup is treated in the same way as a feed to the crystallizer.

The pH of the aforementioned syrup aliquot is adjusted to 3.94 and evaporated at 73 ° C. to increase solids. 2 liters of this solid syrup is placed in a sealed stirred flask and immersed in a constant temperature bath maintained at approximately 55 ° C. During preparation of the second sample (approximately 5 hours), the sample ("sample with pH 4") is continuously stirred in a constant temperature bath.

The pH of the second aliquot of 95% fructose syrup is adjusted to 5.48 and evaporated at 77 ° C. to increase solids. This evaporation is completed more slowly than with a sample of pH 4. Two liters of the sample (“sample with pH 5.5”) are placed in a sealed stirred flask and immersed in a bath of constant temperature containing a sample having a pH of 4.

After adjusting the temperature of the bath to 55.5 ° C., 50 g of fructose seed crystals are added to all samples. Stirring is continued for 60 hours at constant temperature. This time is the approximate crystallization residence time of the syrup for the ACF method described herein.

The resulting bag is sampled and centrifuged, and the mother liquor is analyzed with a sample of the feed syrup. The analytical data obtained is shown in the table below.

Anhydrides are calculated from the difference in the fructose assay before and after hydrolysis of the sample. Fructose solubility is calculated from the fructose assay (prior to hydrolysis) and the solids content of the sample. Some of the fructose in both sample solutions is crystallized to equilibrate.

The color increase in the sample at pH 5.5 is significantly greater than that observed in the sample at pH 4. The brighter the color, the lower the yield for the crystallization process as long as washing of the centrifugal cake is required. The need for mother liquor purification also increases similarly.

All samples had a similar increase in anhydride during feed preparation (compared to 0.27% dsb at pH 4 and 0.24% dsb at pH 5.5), but liquid chromatography investigation (not shown above) showed pH In 5.5, more difructose dianhydrides can be formed.

In summary, samples at pH 4 have less color formation, show a decrease in total acetaldehyde content, and have solubility that is not significantly different from pH 5.5 samples. Thus, in terms of the quality of the mother liquor as a result of product yield and its low color content, a feed syrup having a pH of 4 is more advantageous than a feed having a pH of 5.5 for the ACF process. Low pH clearly minimizes color formation and difructose formation and has little effect on solubility.

As shown in FIG. 3, pH adjustment is conveniently made after fractional separation and before carbon treatment. Since the viscosity of the fructose solution is relatively low at this point in the process, it is relatively easy to obtain by mixing the solution with the acid or base used for pH adjustment. Many acids or bases suitable for this purpose are known in the art. Particular preference is given to hydrochloric acid for lowering the pH, and sodium carbonate anhydride (for example, Na ₂ CO ₃ , “so many times”) for raising the pH.

[Carbon treatment]

The 95 +% (dsb) fructose feed stream for the crystallization process is preferably carbonized prior to concentration by evaporation. One purpose of the carbon treatment is to remove impurities that can inhibit crystallization. Another object is to remove impurities such as colorants, HMF, furfural and acetaldehyde, which adversely affect the quality of the mother liquor and consequently impair its use as a liquid sweetener component. The carbon treatment is preferably performed using carbon granules as a dose of about 1 to 3% anhydrous material, or typically using a lower volume of carbon powder than carbon granules. The temperature of the syrup is preferably about 160 ° F. and typically 15-30 ° F., and the syrup is preferably about 20 to about 25% by weight per anhydrous substance.

Carbon treatment is most advantageously carried out after fractional separation and immediately before evaporation. Carbon treatment at low solids concentrations has been found to lower the fructose loss to difructose to less than 0.5%. If the carbon treatment is carried out after evaporation, the fructose loss is expected to exceed 2.5%. A syrup temperature of approximately 160 ° F (compared to 140 ° F) inhibits the growth of microorganisms in the carbon adsorber, and the lower the syrup viscosity, the better the diffusion into the carbon particles.

EXAMPLE

The amount of difructose formed in an aqueous solution of at least 95% (dsb) of fructose at various dry solids is measured. In two trials first, the aqueous solution is mixed with 2.7% carbon granules (anhydrous solids weight of the carbon granules in the anhydrous solids of the aqueous solution) in the flask and stirred at 160 ° F for 24 hours. Samples are collected after 0, 6, 14 and 24 hours to determine the amount of difructose contained therein. This result is shown below.

The data above show that difructose forms faster in solution at 50% ds compared to 25% ds.

The following four trials were designed to simulate the operation of an industrial scale carbon treatment tower in a plug flow manner, ie, compared to the static system of agitated flasks and deflecting in a dynamic flow system. It is designed to measure todose formation.

Run two 12-inch glass columns in series to ensure the residence time of the syrup feed is approximately 20 hours. Short coils of stainless tubing used for column and feed preheating are immersed in a controlled water bath.

To simulate the backflow of carbon at rest, the column was initially conditioned to run and partially consumed carbon, then the second column was slugged with raw activated carbon granules, approximately 2 Inches of freshly prepared carbon are placed at the outlet of the column.

Four different conditions are tested using the device:

(Use new conditioned carbon granules for each condition)

70% ds at 140 ° F

70% ds at 160 ° F

50% ds at 160 ° F

25% ds at 160 ° F

Each of the conditions listed was performed without recycle for 36 hours using the feed continuously and after 0, 6, 14, 24 and 36 hours the amount of difructose in the column eluate is shown below:

Formation of difructose at 70% ds at 140 ° F has been shown to be no problem, but lower temperatures mean increased risk of microbial growth and higher syrup viscosity. All tests with a higher solids content at 160 ° F (50% and 70% ds) had substantially lower levels of difructose over that time, although the exposure time to heat and carbon was the same in all samples collected. It continues to increase. Without incorporating any special theory, the formation of difructose is catalyzed and / or cocatalyzed by a material that is removed from the aqueous solution by carbon, so that the accumulation of such material on the carbon is determined by fructose over the lifetime of carbon. It can be interpreted that it increases the conversion rate to difructose.

A carbon check filter can be used on the syrup leaving the carbon column to remove all carbon fines in the stream. All insoluble matter that passes through the crystallizer is centrifuged with crystalline fructose and subjected to product quality. Effective filtration is important because it has a direct impact.

Since uncrystallized fructose is blended into a liquid sweetener, carbon treatment also improves the quality of the material. In general, since EFCS is carbonized near the end of the process (ie after blending), the mother liquor from the centrifuge is purified in two carbon treatments depending on the time it becomes the final product.

[Crystalizer Feed Evaporator]

The driving force for crystallization is the degree of supersaturation obtained by cooling the high fructose syrup below its saturation temperature. Saturation curves for fructose (concentration versus saturation temperature) are very steep. In order to achieve a theoretical crystallizer yield in the range of 40 to 55%, for example 40 to 48%, the fructose feed syrup is required to cool to approximately 45 to 55 ° F, for example 47 ° F.

During the evaporation step, water is removed from the feed syrup to concentrate the fructose until it crystallizes out of solution when the fructose is cooled. The evaporator is preferably designed and operated to concentrate the solution while minimizing the thermal damage of the syrup. One preferred method of carrying out the evaporation involves a two step process. The feed syrup is first concentrated in six moving tubular falling membrane evaporators with multiple effects and mechanical recompression. The 95 +% (dsb) fructose stream from the carbon treatment step is fed to the evaporator at a temperature of about 190 ° F and a pH of about 3.7 to about 4.3, at about 20 to about 25 weight percent of anhydrous material. The discharge at this stage is a syrup having about 55 to about 65 weight percent of anhydrous material.

In the second evaporation stage, the discharge from the first stage is fed to a plate-type rising membrane, single effect evaporator operated in Hg vacuum of about 23 to 24. The discharge in the second stage is a syrup having about 88 to about 90 weight percent of anhydrous material at about 165 to about 175 ° F. More preferably, the evaporator is operated at about 26 Hg vacuum with a product temperature of about 140 to about 150 ° F to minimize loss of fructose.

An important criterion in the design and operation of the crystallizer feed evaporator is to concentrate the solution with minimal thermal damage to the syrup. The biggest problem of thermal damage to the crystallizer feed syrup is the conversion of fructose to difructose, which reduces the yield in the crystallizer. Difructose is advantageously formed by high temperatures, high concentrations and long residence times in the evaporator. Since the concentration is necessarily fixed, the design and operating time are chosen to minimize the temperature and residence time of the syrup in the evaporator.

Suitable evaporators such as tubular falling membranes and plate-like rising membranes are generally known in the art.

[crystallization]

The crystallization of fructose can be carried out in batch or continuous crystallizers. Both batch and continuous crystallization have advantages and disadvantages. Batch crystallization is flexible in producing different crystal size distributions and can more easily and quickly control the agitation of the process. However, batch crystallization has lower crystallizer productivity (loading, load removal and taking time to seed the crystallizer); It is more difficult to obtain a consistent crystal size distribution between batches; Feed and bag storage tanks must be large to keep batch circulation time to a minimum; Each crystallizer requires a separate cooling system. Continuous crystallizers have the opposite advantages and disadvantages.

Crystallization may be accomplished in single pass or multiple passes. However, single pass is preferred. For two pass crystallization, only 88% yield per batch was achieved and the crystallization time was estimated to be 87% longer. Moreover, the mother liquor from the two-pass crystallization is more viscous due to the high sugar concentration level and, in the case of two-pass bags, the slurry density (pounds of crystals per hundred pounds) is lower. All of these factors tend to reduce centrifugal productivity.

In the case of liquid sweeteners, the usefulness of the mother liquor as the blending stock solution depends largely on the purity of the mother liquor. The exact level of by-products that can be tolerated or efficiently removed from the mother liquor depends on various factors, but steps should minimize the formation of by-products in the crystallization portion of the process. As long as crystallization is essentially selective for fructose, the byproducts tend to concentrate in the mother liquor upon each successive crystallization. Thus, this problem is exacerbated when passing through a large number of crystallizations so that the byproduct concentration in the mother liquor often imposes an upper limit on the number of crystallization passes that can actually be used in the present integrated process.

Color, ash, HMF, furfural and acetaldehyde concentrations have been found to tend to increase in the mother liquor during multiple crystallization passes. Of these, since the color is clearest most quickly, color is generally a factor that determines the number of crystallization passes that can be used efficiently.

Appropriate means for maintaining the purity of the mother liquor include careful control of evaporation, carbon treatment and crystallization conditions (eg pH, temperature and residence time). Preferred conditions are described in the paragraphs of this document devoted to the various steps of the present process.

Syrup feed to the crystallizer is preferably cooled to approximately 140 ° F. prior to introduction to the crystallizer. In order to obtain the theoretical yield of crystalline fructose 40 to 48%, the syrup feed should contain at least 95% (dsb) of fructose and the solids content of 88.5 to 89.7% by weight (nominal 89% d, sb) Should be

The batch is seeded and mixed thoroughly with seed crystals. Seeding temperature (approximately 135 ° F) is based on the predicted d.s% and fructose% of the crystallizer batch. Once the syrup is completely mixed with the seed crystals, samples of the batch should be analyzed to determine the actual saturation temperature. The cooling system of the crystallizer must be adjusted so that the batch reaches a supersaturation range of 1.00 to 1 05 (based on fructose concentration). If the bag is already below this range, cooling should continue even if nucleation does not occur.

Nucleation is the process of forming crystals from liquids, supersaturated solutions (gels) or saturated vapors (fogs). Crystals originate from trace foreign matter that acts as a nucleus. These foreign substances are often provided by impurities. The crystal is initially formed in a small region of the parent phase and then expanded into the crystal by fusion. In the process of the present invention, nucleation is undesirable as long as it can produce crystals of small size. Moreover, when nucleation occurs properly, the distribution of crystal sizes cannot be controlled. For this reason, it is preferable to use seed crystals.

The progress of the crystallization can be indirectly controlled by the fixation point for the cooling water to be adjusted according to the cooling rate scheduled for the bag and the supersaturation level of 1.0 to 1.35, for example 10 to 1.3.

More preferably, the degree of supersaturation is actually measured to directly control the crystallization progression. Supersaturation can be assessed from d.s% of mother liquor alone given in initial d.s% and and fructose%. Supersaturation data can be used to determine whether to continue the batch according to a predetermined cooling curve or to change the cooling rate to maintain the desired degree of supersaturation.

One preferred method of performing crystallization is an average of 95 +% (dsb) fructose syrup having an anhydrous substance of about 88 to about 90 weight percent, a pH of about 3.7 to about 4.3 and a temperature of about 130 to about 138 ° F. Seeding with about 7 to about 10 weight percent of seed crystals having a particle size of about 150 to about 250 microns. The seeded syrup is then adjusted to cool to crystallize fructose in solution.

Cooling can be performed as follows: when the syrup temperature is about 138 to about 115 ° F., the syrup is cooled at a rate of about 0.5 ° F./hour; If the syrup temperature is about 115 to about 86 ° F., the syrup is cooled at a rate of about 1.0 to about 1.5 ° F./hour. It is recommended to keep the supersaturation level below about 1.17 when the syrup temperature is above about 115 ° F and to maintain the supersaturation level below about 1.25 when the syrup temperature is below about 115 ° F. The maximum temperature difference between the coolant and the bag is preferably about 10 ° F. Too high a temperature may result in nucleation.

However, the cooling is preferably adjusted at different speeds for at least three periods. For example, during the initial period, when the temperature of the syrup is about 138 to about 125 ° F., cooling is performed at a rate of about 1.0 to 1.5 ° F./hour and the supersaturation level is maintained at about 1.20 or less. During the critical period, when the temperature of the syrup is about 125 to about 110 ° F., the cooling rate is preferably about 0.5 to about 1.0 ° F./hour, and the supersaturation level is maintained at about 1.17 or less. And during the rapid cooling period, when the temperature of the syrup is about 110 to about 86 ° F., the cooling rate is preferably about 1.5 to about 2.5 ° F./hour, and the supersaturation level is maintained at about 1.25 or less.

Preferred cooling methods have been found to include automatically adjusting the coolant temperature while continuously monitoring the supersaturation level. In a particularly preferred method, the data processor continues to accept information about the bag temperature, coolant temperature and supersaturation. The processor then uses this information to adjust the coolant temperature by adjusting the coolant temperature. This data processor is first programmed to cool the bag at a rate of 2.5 ° F / hour from its seeding temperature (Ts) to a predetermined threshold temperature (T '), where the threshold temperature is at a temperature of supersaturation levels of 1.17. Calculated from the fructose% and ds% of the crystallizer feed). The program then provides for cooling the bag at a rate of 1 ° F / hour from T 'to 115 ° F and at a rate of 1.5 ° F / hour from 115 ° F to the final temperature (typically 86 ° F). do. However, the program has been overridden to prevent nucleation. First of all, the program ensures that during any cooling, the temperature difference between the bag and the coolant does not exceed the predetermined temperature (typically about 14 ° F) at any time. Second, the program ensures that at any time during the cooling, the supersaturation level does not exceed the predetermined value (typically 1.28). The specific temperatures and rates described above can be varied to optimize the curve for a given set of crystallization conditions without undue experimentation. The main factors affecting temperature are the total dry solids level (ds%) and the total surface area of the seeds. For example, as the dry solids level increases, the critical period will shift to the previous range in the cooling curve and vice versa. If the total surface area of the seeds is reduced, for example if the amount of seed loaded is reduced, the critical period will be extended, and vice versa.

Crystallization Kinetics

[Saturated]

In crystallization kinetics, the growth rate is a function of the concentration driving force-concentration present in the mother liquor versus the concentration that can exist at equilibrium temperature.

Supersaturation is a measure of concentration driving force. There are several ways to define supersaturation. For fructose crystallization, the supersaturation defined by water is found to be the most reliable for the purpose of monitoring the progress of the batch. That is, the degree of supersaturation is defined as the ratio of the fructose g / g of water present in the supersaturated syrup to the fructose g / g of water obtained at equilibrium:

Ideally, the batch cooling rate should be adjusted to control the supersaturation level of the mother liquor. In the crystallization of fructose, it has been found that an acceptable yield of crystals is obtained within the preferred size range when the supersaturation range is 1.0 to 1.30. Batch cooling time is extended when the supersaturation level is below this range, but nucleation is difficult when the supersaturation level is above 1.35.

[Nucleation]

Exchanges are possible in selecting targets for supersaturation. Fructose appears to have no detectable metastable zones, ie supersaturated regions where nucleation does not occur. The growth of existing crystals always competes with the birth of new crystals (nucleation). As the level of supersaturation increases, the growth rate of crystals increases, but the rate of nucleation increases. The goal is to find the supersaturation level at which the desired crystal size is produced within an economically favorable cycle time.

The nucleation described above is of the "shower" or "shock" type. As mentioned above, fructose crystallization is always accompanied by nucleation. Once seeding begins at the beginning of the batch, 쇽 nucleation may occur at the initiation site, which is believed to be due to the low seeding temperature, if nucleation occurs, it is desirable to heat the bag to remove the nucleus. .

The preferred way to avoid nucleation is to maintain supersaturation levels below 1.30 after seeding. The mass nucleation greatly increases the viscosity of the bag, so the purging time is greatly increased, making centrifugation very difficult. Fine crystals separated from the bag are very difficult to dry and tend to aggregate more easily. Mass nucleation undesirably results in products with average crystal sizes of small size.

It has been observed that a 95 gallon syrup batch in a 100 gallon crystallizer requires a cooling cycle of about 30 to 80 hours, and fructose crystallization generally requires a cooling cycle of about 30 to 40 hours. It is preferred that during this period the syrup is cooled at a number of, preferably three different rates. The need for different cooling rates is a result of the nonlinearity of fructose crystallization. The various rates correspond to different growth periods found during the cooling process.

Initial cooling temperatures correspond to temperatures in the region below about 120 ° F. The target cooling range is about 1-4 ° F./hour; Typical rates are 2 ° F / hour, so this period takes 4 to 6 hours, preferably about 8 hours. During this time the seed crystals grow almost completely and the slurry density gradually increases. Most of the heat loaded in the coolant is generated by removing the heater.

Nucleation of the batch can occur in this region, but this only occurs if the seeding temperature is very low or the supersaturation exceeds 1.3.

In the "critical period" the growth rate is increased by two to four factors. Slurry density increases rapidly, creating new crystals and growing to the desired size range. Competitive processes of both crystal growth and nucleation are accelerated.

The boundaries of these areas are not clearly defined. The closest evaluated area is between 120 and 110 ° F. Care should be taken in this area as the nucleation process is dominant and therefore uncontrollable. It has been found that by maintaining an appropriate level of supersaturation (1.05-1.20), nucleation can be maintained within acceptable limits. A preferred method for controlling the degree of supersaturation is to lower the cooling rate. In this region, a cooling rate of about 0.5 to 3.0 ° F / hour, typically 0.5 to 1.5 ° F / hour, is recommended. The estimated time of the critical period at this rate is about 10 to 40 hours, preferably about 18 to 22 hours.

In some situations, high supersaturation levels may not result in nucleation. In this case, additional cooling may result in the formation of fructose hemihydrate. This type occurs in the form of acicular crystals that form slurries with very high viscosity (above 800,000 cps). This slurry is not centrifugal and can even overload the crystallizer drive. The hemihydrate can be detected during a general crystallographic test that must be performed throughout the cooling process.

Once the critical period is complete, the slurry density is sufficiently high to support a rapid cooling rate that does not nucleate. In this rapid cooling zone, the coolant temperature can drop quickly. A per cent cooling rate of about 1 to 7 ° F./hour, preferably about 1 to 4 ° F./hour is recommended. To cool from 110 ° F to a final temperature of about 100-75 ° F, about 3 to 12 hours, typically 8 to 12 hours are required. Faster cooling can be achieved without nucleation, but growth rates are not maintained, leaving higher levels of supersaturation at the end of deployment. Some residual supersaturation can be mitigated by placing bags in a minger or mixer tank for a period of time.

Cooling can be made more quickly in a faster cooling period than in the previous state of the batch, but there are limitations to the method that allows for significant temperature differences between the coolant and the bag. This limit is not known in detail, but due to the cooling rate, the temperature difference between the bag and the cooling surface should not be greater than about 15 ° F. Larger temperature differences can cause nucleation and contamination of the cooling surface.

[Seed]

The seeding temperature can be derived from the saturation temperature of the entire crystallizer mother liquor. To obtain this information, liquid chromatography and refractive index of the feed syrup can be used. The fructose concentration is then calculated using% fructose and ds% of feed syrup. Seeding should be performed within a supersaturation range of 0.96 or greater, for example, 1.0 to 1.10.

The seed is most preferred anhydrous crystalline fructose with an average crystal size of about 100 to 400 microns. Dropping of 1 to 20% (dsb) is recommended. The loading depends on the desired particle size in the final product. The seed should be added to the entire crystallization effort, making every effort to distribute it evenly within the crystallizer. As mentioned above, US Pat. No. 4,164,429 describes a method and apparatus for obtaining crystallized seeds.

Seeding is preferably carried out by first mixing the seed crystals with fructose feed syrup to obtain a liquid slurry for crystallization addition. This has the effect of conditioning the surface of the seed crystals. Producing seed crystals in the syrup also minimizes the formation of bubbles in the crystallization vessel upon seeding. Bubbles are sites where nucleation is possible.

Constant seeding is a major problem in providing the same surface area for the growth of fructose crystals. In general, as the particle size increases, the ratio of the surface area to volume of the seed crystals decreases, so that when the size of the seed crystals increases, a larger mass of seed crystals is required to obtain the desired surface area.

Also, about 5-30%, preferably about 10-20%, of heel can remain in the crystallizer to act as a seed. This process takes much less effort than using anhydrous seeds, but on the one hand the finer particles removed during centrifugation and anhydrous steps remain in the hill, resulting in a wider crystal size distribution. The use of this method yields large crystals which must be pulverized continuously to meet the size specifications of the fine product crystals.

A preferred process is to add hot syrup to the top of the heel. The hot syrup will raise the temperature of the Baek Hill to the estimated saturation temperature (approximately 133 ° F), during which the feed syrup is cooled to the seeding temperature. Some amount of crystals may be lost during the process. Notwithstanding this fact, the final seed density should preferably be in the range of 2 to 10% (dsb) or more. The critical part of the process is the final temperature reached by the feed syrup and baggage hill. At this point the supersaturation level is between 1.00 and 1.10. In this range, seed loss will be minimized and nucleation will be less.

EXAMPLE

Fructose crystallization is carried out using a feed syrup comprising 95.82% (dsb) of fructose at 89.60% anhydrous at the test scale level of a conventional crystallizer. The crystallizer used has a center shaft agitator. Cooling is performed through an internal pin coupled to the central shaft. The crystallizer is almost completely filled with 102 gallons of syrup. Cooling is completed within about 40 hours after seeding, but significant supersaturation (1.17) is maintained at the end of this period. Batch is monitored as a change in supersaturation.

Seeds are prepared by grinding the crystalline product through a 2A Fitzmill screen. The ground material is screened through a 55-mesh screen and a 100-mesh screen. The average size of this seed is 161μ. Anhydrous seeds are added directly to the syrup in the crystallizer.

Table IV shows the cooling programs actually used during the crystallization. Supersaturation rises up to 1.26 during the first 18 hours of execution. This is then dropped to near 1.17, which is maintained throughout the rest of the cooling process.

The average size of the product crystals is 268μ. Crystal yield is 46% based on the fructose content of the syrup.

[detach]

As a method of separating the fructose crystals from the mother liquor, centrifugation with a basket centrifuge is preferable. It has been found that about 4 gallons of bag in a 14 "x 6" centrifuge can be separated in about 10-15 minutes. This period involves one to three, typically two washes with hot water (120-200 ° F.). High wash water temperatures can increase fructose decomposition and result in loss of yield. Amounts of wash water are recommended between 1 and 5% based on the weight of the bag. Deionized washing water may be used. The pH range of the wash water is preferably about 3 to 5.

Preferred operating conditions for the basket centrifuge used to remove crystalline fructose from the mother liquor include: a gravity of about 1400; A cake thickness of about 2 to about 3 inches; Cake moisture with a moisture of about 0.7 to about 1.5% and product purity of at least about 99.5%, more preferably at least about 99.8%. Cake moisture and purity are considered important criteria for producing a non-aggregated and stable product.

The product cake is preferably removed after washing during centrifugation. A preferred wash is to use water at a temperature of about 150 to about 180 ° F. for an amount of about 1 to about 1.5 weight percent of baggage charged to the centrifuge. Using this method, it has been found that typically about 5 to about 10% of the product is lost during washing. Washing water containing dissolved fructose can be recycled to a carbon treatment step for impurity removal and continuous reconcentration.

[dry]

Various dryer forms can be used for this process. Fluid bed dryers, vibrating fluid bed dryers, trays and rotary dryers are all suitable. Preferably, the wet cake from the centrifuge is metered into a continuous mixer via a screw conveyor of varying speed. Anhydrous recycle material is metered through a choked conveyor (to prevent air bypass) at a nominal ratio of 4: 1 or less for the wet cake. The action of the mixer should be sufficient to completely blend the wet and anhydrous material. The blended cake is then transferred to a dryer.

The cake is preferably dried at the same time to prevent the product from overheating. First, the room air is purified by passing through an ultra fine borosilicate filter at a rate where 95% of the 0.5μ particles are removed. Subsequently, in the dryer inlet, when mixed with air discharged from the cooler, it is heated to a temperature that produces air at a temperature of 160 ° F.

The product moves from the dryer at about 130 ° F. and is delivered to the cooler. The adjusted amount of product is recycled to the dryer main inlet without cooling to process the wet centrifugal cake. The most critical and variable in the drying process is the moisture of the cake to be introduced. If there is too much moisture, the dryer will produce balls and flocculation products. Moisture can be controlled by the ratio of dry recycle to wet cake. Although the ratio of the 2: 1 dry recycle to the wet cake is generally satisfactory for forming crystals, nucleated crystals are poorly centrifuged and a 3: 1 ratio may be required to prevent aggregation.

The centrifugal cake is preferably dried in a rotary dryer to lower the moisture of the fructose crystals to about 0.1% by weight or less. When the water content of the centrifugal cake exceeds approximately 1.5% by weight, lumps have been found to form in the dryer. As noted above, anhydrous product recycle can be used to control centrifugal cake moisture. It is recommended that the product temperature not exceed about 140 ° F. Preferred dryer operating conditions are as follows: inlet air temperature is from about 170 to about 250 ° F, more preferably from about 170 to about 200 ° F; Exhaust air temperature is about 130 to about 145 ° F; Product temperature is about 125 to about 135 ° F .; The product moisture content is about 0.1% or less, more preferably about 0.07% or less.

[Conditioning]

If the fructose crystals were stored warming up, they were found to form lumps during storage. This same phenomenon exists in the production of dextrose and sucrose. Although the exact mechanism has not been proven, it is believed that moisture migrates from the larger crystals to smaller crystals, causing further crystallization at the interface. This is the result of a temperature change or moisture change, which occurs because the crystal is not in equilibrium. The test shows that the free flowing product is produced by drying the product to very low moisture (about 0.05%) and cooling it to room temperature. To equilibrate with fructose crystals with 0.05% moisture, the relative humidity of air at 70 ° C. must be 50% or less.

Rotary coolers using countercurrent air are well suited for this purpose. Frozen and dewet (conditioned) air is used to cool the product crystals to about 75 ° F. or less, more preferably about 72 ° F. or less. Inlet cooling air is recommended for temperatures below about 70 ° F and relative humidity below about 40%. The residence time in the cooler should be sufficient to ensure that the crystals are properly conditioned. The final product moisture content is preferably about 0.07% or less.

The final product can be sized by screening and / or grinding. Long term storage of the product at high temperatures will cause cake formation and color problems even if stored in a moisture barrierbag. Warehouse storage should be done under controlled humidity conditions.

[Blend]

The mother liquor separated from the crystalline product during centrifugation can be returned to the EFCS portion of the process.

In addition to mixing the mother liquor and dextrose remaining after separation of the crystalline fructose, the mother liquor can be simply diluted with water to produce VEFCS.

Following separation of the crystalline fructose, the mother liquor can be mixed with dextrose or dextrose-containing solution to finally produce a liquid sweetener comprising dextrose and fructose such as 55% HFCS (EFCS). As shown in Figure 3, a number of dexrose containing streams may be blended with the mother liquor prior to introduction into the final finishing operation. The selection of a particular stream or streams allows consideration of mass balance and the desired fructose in the final liquid sweetener product. Can be indicated according to the level goal. The most common level of integration is with a fructose of 55% (dsb). If sufficient fructose is present in the mother liquor, it is also possible to blend the dextrose product stream from saccharification (typically 94-96% (dsb) dextrose) for introduction into the EFCS finishing process.

In addition, liquid sweeteners can be prepared by simply diluting the mother liquor, typically having a fructose of 90-92% (dsb), as water. If the solution is not diluted below the saturation point at all temperatures used, it is recommended to dilute the fructose contained in the mother liquor, if desired, as long as additional fructose crystallizes from the mother liquor. In addition to water, other suitable diluents include dextrose syrups, aqueous sugar solutions such as HFCS, EFCS, VEFCS, and preparation streams for such syrups. Other methods of inhibiting the crystallization of fructose in the separated mother liquor include preventing or inhibiting evaporation of water from the solution and incorporating additives for inhibiting crystallization.

Another use for an isolated mother liquor or part thereof is to prepare an amorphous or semicrystalline fructose sweetener. One way to achieve this is to disperse the mother liquor onto an edible particulate solid and then to dry the dispersion to produce a sweetener comprising fructose in amorphous or semicrystalline form. Preferred edible particulate solids for this purpose are crystalline fructose.

US Pat. No. 4,517,021 describes a method of making a semicrystalline fructose composition. The teachings of this patent are incorporated herein by reference. The isolated mother liquor of the present invention can be used as an aqueous fructose syrup of the above method, and crystalline fructose can be used as a crystallization initiator. Thus, an integrated method for preparing one or more liquid sweeteners comprising crystalline fructose, semicrystalline fructose, and fructose is provided.

The above description relates to certain aspects of the present invention in accordance with the requirements of US patent status for enumeration and clarification purposes. However, this will be apparent to those skilled in the art and many modifications and variations of the apparatus, compositions and methods set up are possible without departing from the scope and spirit of the invention. The scope of the following claims is to be construed as including all such modifications and variations.

Claims (10)

Splitting the fructose and dextrose containing aqueous stream into first and second streams, fractionally separating the first stream to produce a high fructose stream, crystallizing fructose from the high fructose stream, and depleting fructose At least a portion of the prepared high fructose stream is combined with said second stream to produce a liquid sweetener containing crystalline fructose and fructose and dextrose. The method of claim 1, wherein the aqueous solution containing textrose is subjected to treatment so that a portion of the dextrose in the solution isomerizes to obtain an aqueous solution containing fructose and dextrose. The process of claim 1 or 2, wherein the fructose crystallization is performed at pH 3.7 to 4.3. The process according to claim 1 or 2, wherein the fructose-containing aqueous solution is subjected to carbonization and then subjected to a solvent evaporation step before crystallizing fructose from the fructose-containing aqueous solution. The solution of claim 1 or 2, wherein the aqueous solution containing fructose and dextrose is fractionated to separate dextrose-rich solution, the first fructose-containing solution and the second fructose-containing solution, wherein the second fructose-containing solution is used. The fructose content of the solution is higher than the fructose content of the first fructose-containing solution), crystallizes fructose from the second solution or a solution derived therefrom, and the resulting fructose depleted solution is obtained from the first The solution and dextrose concentration (dsb) is added to the aqueous solution containing dextrose larger than the first solution. The process of claim 5, wherein the fructose and dextrose containing solution is divided into first and second streams, the first stream is subjected to fractional separation and fructose crystallization, and the second stream is subjected to the first solution and dextrose. A method of adding to a solution depleted of fructose as an aqueous solution. Crystallizing fructose in an aqueous solution of fructose to produce a mixture comprising crystalline fructose and mother liquor; Separating crystalline fructose from the mother liquor and inhibiting further crystallization in the mother liquor to produce a liquid sweetener comprising fructose, the method of producing crystalline fructose and liquid sweetener. Fractionating the stream comprising dextrose and fructose to produce a high fructose stream having a fructose greater than 90% (dsb); Contacting the high fructose-containing stream with activated carbon to produce a purified fructose stream; Evaporating the purified fructose stream to produce a fructose solution, and crystallizing the fructose in the fructose solution. Crystallizing fructose in a fructose solution to produce a mixture of mother liquor comprising crystalline fructose and fructose; Separating crystalline fructose from the mother liquor; Mixing at least a portion of the fructose of the mother liquor with an aqueous liquid to form a low solids solution of fructose; Contacting activated carbon with a low solids solution of fructose and evaporating the low solids solution of fructose to form a high solids solution of fructose. Cooling the fructose solution over the initial temperature range at an initial cooling rate; Cooling the solution over an intermediate temperature at an intermediate rate slower than the initial cooling rate and cooling the solution over the final temperature range at a final rate faster than the intermediate rate. Manufacturing method.