Classifications

• • C—CHEMISTRY; METALLURGY
  • C13—SUGAR INDUSTRY
  • C13K—SACCHARIDES OBTAINED FROM NATURAL SOURCES OR BY HYDROLYSIS OF NATURALLY OCCURRING DISACCHARIDES, OLIGOSACCHARIDES OR POLYSACCHARIDES
  • C13K5/00—Lactose

Definitions

• the present invention relates to methods of producing a powder of lactose from aqueous slurries comprising crystals of -lactose monohydrate and dissolved lactose, whereby improved control of the ratio of amorphous to crystalline lactose in the powdery lactose product is obtained.
• BACKGROUND Lactose is an important by-product of the dairy industry with many important uses such as infant nutrition and in pharmaceutical products. It is a water soluble molecule present naturally in milk wherein it makes up 2-8% of the milk by weight.
• Lactose in aqueous solution has two anomeric forms, Ga ⁇ lactose and ⁇ -lactose which in solution are dynamically in equilibrium and can mutarotate to maintain their equilibrium.
• crystals of a-lactose are obtained from aqueous solution by crystallization.
• the a-form is less soluble than the ⁇ -form at a given temperature below approximately 93°C and the a-form reaches the point of supersaturation first and forms crystals of a-lactose monohydrate when crystallized from aqueous solution.
• no distinguishing will be made between crystals of ⁇ -lactose and crystals of a- lactose monohydrate, as the resulting product of crystallization from aqueous solution is always the Ga ⁇ lactose monohydrate crystal form.
• amorphous lactose has basically no buffer effect regarding water activity, meaning that for practical purposes it does not absorb or desorb water.
• amorphous lactose has a significant buffer effect regarding water activity up to a point where the amorphous powder becomes unstable and crystalizes to a-lactose monohydrate while releasing water. It is therefore customary in the art to adjust the ratio of amorphous lactose to ⁇ -lactose monohydrate in dried lactose powders in order to control powder stability and shelf-life. Likewise, it is customary in the art to adjust the amount of amorphous lactose in spray dried lactose products intended as e.g.
• control of powder sphericity is essential, which control depends intrinsic on the ratio of the amount of amorphous lactose to the amount of crystalline a-lactose monohydrate present in the slurries from which the spray dried lactose product is manufactured.
• WO 2012/047122 describes a method of manufacturing a slurry comprising crystals of a-lactose monohydrate by concentration in an evaporator, by feeding a continuous stream of dissolved lactose to a process loop comprising a heat exchanger with a holding cell and the evaporator, wherein the slurry of a-lactose monohydrate crystals is created in the evaporator and subsequently removed by centrifugal clarification in a hydrocyclone above a certain cut-off size, allowing a slurry comprising crystals below the cut-off size to circulate the process loop.
• the ratio of ⁇ -lactose to ⁇ -lactose is determined by the operating temperature of the heat exchanger and the evaporator, but the slurry of crystals of a-lactose monohydrate led to a subsequent dryer is unaltered after passage of the hydrocyclone.
• Figure 1 Flow-diagram of the method of the invention.
• Figure 2 Exemplary process of the invention.
• Figure 3 Exemplary process of the invention. DETAILED DESCRIPTION
• a method for controlling an amount of amorphous lactose in a dried lactose powder comprising: i) supplying a mass-flow (MF) of a slurry comprising a first amount of dissolved lactose and a first amount of crystals of a-lactose monohydrate, said slurry having a total-solids concentration TS and a slurry temperature, Tsiurry, to a dryer for producing a lactose powder comprising amorphous lactose and crystals of a-lactose monohydrate at a first mass flowrate; ii) diverting a fraction, f, of said mass- flow of said slurry to a heater (2) where, in said heater (2), said fraction, f, of said mass-flow of said slurry is heated to a heating temperature, Theat, before being redirected to said mass-flow of said slurry; and v) drying said slurry in a dryer (5)
• the source (1) for the lactose-slurry is a source (1), which can deliver a lactose-slurry which is ready for drying as a final, commercial product, such as a crystallization tank, since the problem of low amounts of dissolved ⁇ -lactose in the slurry does not arise in the process line before crystallization.
• a source (1) which can deliver a lactose-slurry which is ready for drying as a final, commercial product, such as a crystallization tank, since the problem of low amounts of dissolved ⁇ -lactose in the slurry does not arise in the process line before crystallization.
• the slurry extracted from the process loop in WO 2012/047122 which is a concentrated slurry at about the boiling point of water will have an amount of ⁇ - lactose dissolved in water of 90 g/100 g H2O , which is plenty for adequate control of the level of amorphous lactose in a dried lactose powder.
• lactose slurries exiting a crystallizer at e.g. only 10 °C will comprise practically zero dissolved ⁇ -lactose due to the preferential crystallization of -lactose, and therefore cannot provide the levels of ⁇ -lactose necessary for adequate control of amorphous lactose in subsequently dried lactose powders.
• the lactose slurry for use with the present method shall comprise not more than 5 g/100 g H2O of dissolved ⁇ -lactose, not more than 3 g/100 g H2O of dissolved ⁇ -lactose, not more than 2 g/100 g H2O of dissolved ⁇ -lactose, preferably not more than 1 g/100 g H2O of dissolved ⁇ -lactose and most preferably not more than 0.5 g/100 g H2O of dissolved ⁇ -lactose.
• the process disclosed in WO 2016/071397 produces lactose powders with less than 5 g/100 g H2O of dissolved ⁇ -lactose.
• step iii) said fraction, f, of said mass-flow of said slurry (step iii) is held in a holding unit (3) for first holding time, thoid, sufficient to allow at least partial dissolution of said crystals of -lactose monohydrate in said holding unit, before being redirected to said mass-flow of said slurry.
• step iv) said fraction, f, of said mass- flow of said slurry (step iv) is rapidly cooled to a cooled temperature, Tcooi, before being redirected as a supersaturated slurry or solution to said mass-flow of said slurry .
• the effect of heating the slurry comprising crystals of Ga ⁇ lactose monohydrate is that a part, and in some embodiments all, of the crystals of a-lactose monohydrate will dissolve at the heating temperature, Theat, and rapidly mutarotate to establish an equilibrium between dissolved ⁇ -lactose and a-lactose at the given heating temperature, whereby the ratio of ⁇ -lactose to ⁇ -lactose can be influenced in a known manner following the data provided in accordance with Table 1 below.
• the amount of dissolved ⁇ -lactose and ⁇ -lactose at equilibrium in the slurry at the slurry temperature is known from Table 1, and the amount of dissolved ⁇ -lactose and ⁇ -lactose at equilibrium in the fraction of the slurry directed to the heater (2) at the slurry heating temperature is likewise known from Table 1, hence following common, well-established phase-equilibrium calculations, o it can easily be established how much dissolved ⁇ -lactose is redirected to the flow of unheated slurry.
• the additional amount of dissolved ⁇ -lactose supplied by heating the aforementioned fraction of mass-flow of the slurry to the remaining mass-flow of the slurry (MF-f) can now be reliably controlled, and hence, since the amount of dissolved ⁇ -lactose in the slurry is determinant for the amount of amorphous lactose in the final, dried powder, the ratio of amorphous lactose to crystals of a-lactose monohydrate in the dried powder can be controlled to a high precision in the method, when starting from a known starting point, e.g. in accordance with the data of Table 1.
• solubility and reaction rate parameters are given for a- and ⁇ -lactose for the temperature interval from 0°C to 100°C. It can be seen from the table that the ratio of ⁇ -lactose to ⁇ -lactose at equilibrium decreases linearly with temperature, whereas the mutation rate of ⁇ - lactose to ⁇ -lactose is accelerated by increasing the temperature above 30°C. As the crystallization of a-lactose monohydrate is favored when the temperature is below 30 °C it is preferable to keep the crystallization temperature below 30 °C and the mutarotation temperature above 30 °C.
• mutarotation rate is significantly improved and above 60°C conversion is very fast and holding time of only a few minutes give significant mutarotation. As such, short retention times are possible already when the temperature in the holding unit is at 40°C. Upwards in a closed or iso-volumeteric system mutarotation temperatures may exceed 100°C and a mutarotation temperature of about 110°C, of 120°C, of 140°C or even of about 160°C is possible in the method.
• the mutarotation temperature is contemplated to be from 40°C to 100°C, more preferably from 50°C to 90°C and most preferably from 60°C to 80°C. It is preferred in the method of the invention, that the method shall be performed under iso-volumetric conditions.
• the heater (2) for heating the mentioned first volume from the crystallization temperature, T s i ur ry, to the mutarotation temperature, Theat, is preferably a heat exchanger for continuous operation or a boiler for discontinuous operation .
• the holding unit (3) can be constructed according to normal principles as is known to the skilled person.
• the cooler (4) for cooling said first volume from the mutarotation temperature, Theat, to the crystallization temperature, T s i ur ry, is preferably a heat exchanger for continuous operation or a cooler for discontinuous operation.
• Figure 2 details a preferred embodiment of the present invention, wherein a single heat exchanger with a holding- cell is detailed ( Figure 2A) .
• the heat exchanger allows for the heated solution to cool be counter flow in the heat exchanger, whereby both energy and equipment footprint is saved.
• Figure 2B the amount of dissolved ⁇ -lactose is raised in the process according to the method from effectively 0 g/100 g H2O to 14 g/100 g H2O under the given temperature conditions.
• a flow controller can be installed to adjust the return flow (and hence the over-all flow) and thereby the amounts of added ⁇ -lactose.
• a dryer according to the invention can be e.g. a fluid bed dryer or a spray dryer as are known in the art of producing lactose powders from lactose slurries.
• a dryer it is a persistent problem, due to the statistical nature of the drying process, that an undersized fraction of powder is produced, in the art called fines.
• Such fines can be tedious to recycle but can, in the present method, find advantageous use.
• Figure 3 details this aspect of the invention in greater detail.
• the dried fines are mixed into the fraction of the lactose comprising slurry diverted from the mass- flow of the same slurry.
• Crystals were dried after washing using 200 1/h of washing water in the sieve.
• the Aw increased from 0,13 to 0,48 over 48 hours in a sealed container (thin line) .
• the washing water addition to the sieve was stopped and instead 100-150 1/h of pasteurized sieve water was added in the sieve.
• a sample from this product was taken 31 ⁇ 2 hour later and in this sample Aw increased from 0,08 to 0,10 over 48 hours in a sealed container (thick line) .
• Crystals were dried where 150-200 1/h of pasteurized sieve water was added in the sieve.
• the Aw increased from 0,08 to 0,11 over 48 hours in a sealed container (thick line) .
• the pasteurized sieve water was stopped and instead 200 1/h of washing water was added in the sieve.
• a sample from this product was taken 2 hours later, while still drying on the same crystallization tank. In this sample Aw increased from 0,11 to 0,18 over 48 hours in a sealed container (thin line) .

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• 2017
  • 2017-12-13 EP EP17823068.6A patent/EP3555321A1/de not_active Withdrawn
  • 2017-12-13 WO PCT/EP2017/082605 patent/WO2018109000A1/en not_active Ceased

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