IE53236B1 - A process for increasing the uninformity in the structure of proteins in milk - Google Patents

Description

This invention relates to a process for increasing the uniformity in the structure of proteins in milk.

Such a process is known from British Patent Specification B 1,477,018. In the known process, whey is first concentrated by ultrafiltration, then diluted and then treated again by ultrafiltration. However no alteration in the proteins takes place in a physical manner.

Milk is a polydisperse aqueous system which contains water-soluble substances. In their original state, such systems are in a state of equilibrium. The structures of the dispersed substances have adjusted to each other regarding their solubility in water. The microstructure of each dispersed substance has assumed the configuration which corresponds to the quantity of water which is available. For this reason the entire system can be described as being in a state of equilibrium. (Each of the individual systems is also in a water-dependent state of equilibrium).

This state can well be described for milk, which is one of the - 2 5333G most complex polydisperse aqueous systems. Consisting of carbohydrates, enzymes, fat, protein, salts, trace elements, enzymes and certain other substances, milk is a basic foodstuff.

The above-mentioned nutritive substances possess a large number of properties. Some of these are: - Hydrophilic or hydrophobic properties; - foam-forming, gel-forming, thickening properties; - thixotropic, agglomerating, cross-linking properties; - an ability to bind, form or release substances; - buffering, sweetness-increasing, sweetness-decreasing, caramelising properties; - odour-absorbing, taste-influencing, flavor-activating properties; - souring-promoting, acid-binding properties; - energy-releasing, energy-absorbing properties etc.

In original milk, the water-binding property of the substances dispersed in the milk is predominant; all other properties are subordinate to that one property and are not available in the aqueous state.

Besides, owing to influences which are due to the feeding of animals, environmental conditions and an improper treatment, the water-dependent states of equilibrium of the substances dispersed in milk may be unfavourably altered with regard to the processing of the milk.

For instance, the presence of inhibitors, an excessive water content, and an activation of enzymes can often be detected.

Milk exhibiting the last-mentioned undesired features previously had to be rejected or, if they were not recognized in time and were processed, involved substantial losses in production.

In the previous practice, milk was treated regardless of the states of the several dispersed substances and substantial processing - 3 sequences were required to develop a certain necessary property of a certain dispersed substance.

This will be explained with reference to the production of cheese. 5 The production of cheese depends highly on gel-forming, cross-linking and enzyme-forming properties of proteins.

Until recently, the entire system of milk, including all systems 10 of the several dispersed substances, was processed to promote the above-mentioned properties.

Lactose and certain salts as well as the so-called whey proteins all had to be processed too although in the water-soluble state in which they are present they strongly disturb the development of the desired gel-forming properties of casein.

They are then removed more or less in a very late stage of the production process.

In recent technologies, the systems are first subjected to separation processes, such as ultrafiltration or ultrafiltration combined with other separating processes, for instance, vacuum evaporation, so that the contents of dispersed substances which would disturb the development of a certain property of another dispersed substance will be decreased.

For instance, ultrafiltration processes for producing a protein concentrate having different protein contents or ultrafiltration processes for removing water from the systems before their actual ultrafiltration are known and have been adopted to provide a specified protein concentrate regardless of the behavior of the individual systems during the separating steps, their influence on each other and their properties in the concentrate.

In these processes, the entire system is treated in an entirely indiscriminate manner regardless of the influences of the individual systems on each other during the processing, only with the aim to - 4 53 238 provide a specified concentrate having specified contents of individual dispersed substances, regardless whether or not individual systems can still assume water-soluble states and regardless of the behavior of the individual systems can still assume water-soluble states and regardless of the behavior of the individual systems in their incidentally assumed states.

In German Opened Applications 22 11 737 and 27 46 532, reference is made only to the protein content which can be obtained and the final water content which is desired.

In the use of said processes it has been found that concentrates in which the properties of the dispersed substances have been changed arbitrarily and indiscriminately are virtually useless because bitter substances, e.g., may form therein and owing to the uncontrolled particle size distribution of the proteins these concentrates do not permit a controlled cross-linking of proteins.

It is an object of the invention to provide a process by which the microstructures of dispersed substances contained in milk can be matched while the substances are water-soluble.

The present invention provides a process for increasing the uniformity in the structure of proteins in milk wherein a) a partial amount of the milk is preconcentrated by ultrafiltration to at least one and a half times the value of the protein content, b) the preconcentrate obtained is mixed with the remainder of the milk, c) the mixture obtained is concentrated by ultrafiltration to at least one and a half times the value of the protein content, d) a part of the water is extracted from the concentrate obtained by evaporation under vacuum or reverse osmosis at a temperature below 65°C, - 5 3 3233 e) the concentrate obtained is subjected to a further ultrafiltration, f) the concentrate obtained is mixed back with the water obtained in step d), g) the mixture obtained in step f) and the filtrate obtained from the ultrafiltrations are each subjected to a heat treatment at up to 85°C, and h) the two phases from step g) are mixed.

Preferably in the process according to the invention the relationship of the dispersed substances, whether they are originally contained in the starting material or have been added thereto, are adjusted in quantity, particle size, water solubility and/or equilibrium. If the products are liquid or include the entire original solids content, the liquid which has been removed and which may have been treated or may not have been treated can subsequently be added entirely or in part. Liquid can be subsequently added in a quantity which exceeds the quantity of liquid that has been removed. The separating processes may suitably be carried out at different temperatures or liquid may be subsequently added at different temperatures. The proportions of the dispersed substances originally contained in and/or added to the starting material can be changed by separating processes which are carried out in series or in parallel.

In the process according to the invention, a preconcentrate is prepared and is then diluted with the starting material, which may have been treated or may not have been treated, and the resulting mixture is subsequently subjected to another separating process and additional steps for influencing the microstructures may be adopted during the separating process, if desired, when the substances which are to be concentrated have reached a concentration which exceeds their initial concentration in the mixture or amounts to at least one and a half times said initial concentration in the mixture. When it is desired to produce milk products by ultrafiltration, a preconcentrate is prepared, which may contain substances that are to be concentrated, such as proteins, in twice their initial concentration, and which is then - 6 5 J ο o diluted with treated or untreated milk, whereafter the resulting mixture is subjected to ultrafiltration once more. When the substances to be concentrated, such as protein, have reached a concentration which is at least one and a half times their concentration in the mixture before the ultrafiltration, additional measures for influencing microstructures may be carried out during the ultrafiltration.

The present invention is concerned with controlled influences exerted on individual systems in an overall system. Within the scope of the invention it has been found that in the production of milk proteins it is desirable to develop certain properties of several dispersed substances when these are still water-soluble so that these properties of individual dispersed substances can be utilized in a controlled manner because this will prermit the processing to be carried out with a smaller energy consumption, a higher economy and a smaller pollution of the environment.

In carrying out the invention, separating processes known per se are carried out to effect controlled alterations of the microstructures of the individual systems during the processing in such a manner that initially latent properties which are desired for the processing to produce a given product are developed when the dispersed systems are still in a water-soluble state.

For instance, when skim milk is subjected to ultrafiltration according to the state of the art, the protein which is present is water-soluble and its concentration will be increased. At the same time, the also water-soluble lactose and salts are removed regardless of the microstructural state of the protein. As a result, the proportions will be changed as follows if the protein concentration is increased 1:5: Ratio of contents Ratio of contents in starting milk_in concentrate parts casein to 5 parts casein to part protein 1 part protein - 7 0.6 part casein to 1 part lactose 2.5 parts casein to 1 part lactose 0.8 part casein to 5 1 part ash parts casein to 1 part ash parts casein to 1 part calcium .3 parts casein to 1 part calcium As a result of that change in proportions, protein micelles divide to form sub-micelles and the stability of that protein is so strongly changed that subsequent process steps result in great demage and cannot be optimized.

These unfavourable alterations of the microstructures of the substances dispersed in milk result from all separating processes carried out thus far because they result in substantial changes of the proportions of all or some substances dispersed in the milk regardless of their states of equilibrium and the influences thereof on the microstructures of the several dispersed substances.

For this reason the invention calls for such a combination of separating processes that the changes in the proportions of the substances dispersed in milk result in such alterations of the microstructures of the substances dispersed in milk that desired properties of the end product are already present in the starting product or are so prepared therein that final states can be stabilized.

This will be explained with reference to the production of certified milk, cheese, sour milk products, and fresh cheese. 1) Production of Milk for drinkino In the production of milk for drinking, a legally prescribed heating process is required, in which states of equilibrium of various dispersed substances are changed in an entirely indiscriminate manner; this results in undesired changes of properties.

For instance, a high-temperature heat treatment will result in an - 8 8 3 2 3 0ί as-boiled taste and oxidized taste, an ultra-high-temperature heat treatment will result in caramelizing and in a lower stability of proteins, and short-time heat treatment will result in a slight as-boiled taste and in an inadequate sterilization.

For this reason the invention as defined above provides a process of exerting a controlled influence on the microstructures of dispersed substances by means of known separating processes, which are systematically carried out to exert such an influence on individual structures that a subsequent heat treatment will not result in uncontrolled changes of properties so that, e.g., undesired changes of flavour will be avoided.

When the starting product is a satisfactory original raw milk which is to be subjected to an ultra-high-termperature heat treatment, uncontrolled changes of the microstructures of the proteins, of lactose, or of the salts, and microstructural reactions of lactose and proteins must be prevented.

In the process according to the invention, milk is first subjected to a moderate ultrafiltration in order to increase the concentration of protein by a small percentage and effect a relative decrease of the contents of lactose and salts. In that step, the microstructures of the protein particles which are present are made more uniform.

The polydisperse microstructures are reduced in size toward monodisperse forms. This will reduce the stability of the solution of protein in water. Without additional measures, subsequent heating steps would considerably demage the protein. For this reason, a subsequent separating process by which only water is removed would have the result that the protein particles having a uniform, small size are uniformly increased in size, the surface of the total protein is reduced, the polarity which acts outwardly is increased and the ability to bind water is thus increased.

As a result of the preceding ultrafiltration, all protein particles can be uniformly increased in size in a succeeding - 9 5 3 2 3 6 evaporating step so that an approximately monodisperse structure is obtained, which has a very stable state of equilibrium.

The substances removed by the separating process (permeate and 5 water) are added to the thus treated milk because the protein particles which have been increased in size will violently bind that liquid without an alteration of their structure. That effect can be assisted by a variation of temperature during the addition or by separate treatments of the two phases at different temperatures.

The microstructures can be further improved if, e.g., electrodialysis processes are used too.

In practice, the process can be carried out as follows: It is desired to produce 10,000 liters of milk that has been subjected to an ultra-high-temperature heat treatment. The milk contains about 2.9% casein, 0.6% protein, 4.7% lactose and 0.7% salts. The total solids content is about 8.9%. a) Production of a Preconcentrate A part of the milk, e.g., 2000 liters, is subjected to ultrafiltration at a temperature below 65°C to obtain a concentrate which contains about .8% casein 1.2% protein 4.7% lactose 30 0.7% salts 11.3% total solids - 10 53236 The filtrate obtained contains about 0,2 % protein 4.7 5 lactose 0.7 % salts and is stored. b) Preparation of a Mixture The remaining part of the milk amounting, e.g., to 8000 liters, is mixed with the concentrate obtained. The resulting mixture amounting to about 9000 liters contains about 3.22 Q. O casein 0.64 s protein 4.68 o. T> lactose 0.70 o. Ό salts 9.24 % total solids c) Ultrafiltration of Mixture The resulting mixture is then subjected once more to ultrafiltration under the above-mentioned conditions to obtain a concentrate which contains, e.g., approximately .00 % casein 1.00 % protein 4.65 % lactose 0.70 % salts 11.35 % total solids.

The filtrate is also stored. 5800 liters concentrate and 4200 liters filtrate are now available. d) Removal of Water Water is then removed from the concentrate at a teraperature below 65° C by vacuum evaporation or reverse osmosis or the like until the concentrate contains approximately 532 3 6 6.30 % casein 1.26 % protein .86 % lactose 0.88 % salts 14.30 % total solids.

About 4600 liters concentrate and 1200 liters of a dilute fraction were obtained. e) Reseated Ultrafiltration To promote a subsequent thermal sterilization, the concentrate obtained in a quantity of about 4600 liters is again subjected to ultrafiltration so that 3000 liters concentrate are obtained, which contain about 9.65 % casein 1.34 -¾ protein .85 % lactose 0.35 % salts 17.69 % total solids, and 1600 liters filtrate containing 20 0.2 § protein .9 % lactose 0,9 % salts 7.0 % total solids. f) Backmixing These 3000 liters concentrate are then mixed with the dilute fraction obtained by the removal of water.

The resulting mixture amounting to 4200 liters contained 6.89 -3 casein 1.39 % protein 4.20 -3 lactose 0.61 % salts 13.09 3 total solids.

In that mixture the protein has such a microstructure that a heat treatment will not result in an as-boiled taste, in caramelizing, in Maillard reactions, and in a decrease of the stability of proteins.

The remaining dispersed substances were obtained with such microstructures that they cannot produce undesired results in combination with protein or as independent structures during the heat treatment.

As a result of the altering of the microstructures of the individual systems, the system can be sterilised at temperatures which are much lower than those used for an ultrahigh-temperature heat treatment. g) Heat Treatments of Different Fractions For this reason it is proposed in accordance with 20 the invention that the at least two fractions obtained in the process are separately heated at temperatures up to 85° c. h) Second Backmixing The two fractions are then mixed when they are still hot or after they have been cooled. The resulting end product is stable and has the original composition.

During the several process steps, the microstructures are influenced as follows; a) Production of a Preconcentrate 30 By the pratreatment of a partial quantity by a . 53.236 separating process consisting here of ultrafiltration, the protein content is increased and the contents of lactose and salts remain substantially unchanged. This is apparent upon a comparison of the composition of the starting milk with the composition of the preconcentrate. As a result, the ratio of the lactose and salt contents to the protein content is decreased. As the system was originally in a state of an unstable equilibrium regarding the relative water solubilities of the microstructures, the production of the preconcentrate makes more water available for the protein so that protein microstructures which had adapted in size to the deficiency of water in the starting material can now change.

As the protein structures are polydisperse in the starting material, the preconcentrating treatment results in more uniform structures having substantially uniform properties. b) Preparation of a Mixture The mixing of the preconcentrate with the remaining 20 starting material increases the quantity of water which is available for the total protein so that the mere mixing results in more uniform protein structures having more uniform properties. c) Ultrafiltration of Mixture As a result of the pratreatment, the desired changes in properties can be much more easily effected by ultrafiltration. Protein microstructures can now be changes in various ways, depending on the nature and direction of the ultrafiltration, In the present example the protein structures are 53236 · first reduced in size until they have all a uniform small size. The succeeding removal of water (step d)) and the second ultrafiltration then result in a uniform increase in size and in a stabilization of the states of equilibrium.

As a result of the first backmixing (step f)) effected by an addition of water having the properties of a distillate, the protein microstructures have a high degree of freedom of independent movement so that a stable equilibrium and a high thermal conductivity are obtained.

For this reason that fraction can be heat-treated without deterioration.

The second fraction (filtrate) is substantially free from protein and the dispersed substances contained therein have such microstructures that the fraction will not deteriorate in a heat treatment as there can be no browning and no Halliard reaction.

The sterilized, stable product obtained by the second backmixing has not been subjected to an ultrahightemperature heat treatment and for this reason is superior to conventional stabilized milk as regards nutrition physiology and flavor. 2) Production of Cheese Cheese made by conventional methods has a high casein content, a low protein content, and relatively low contents of lactose and salts.

In the production of, e.g., curd by conventional processes, the entire system is subjected to microbial souring, Microorganisms are added to milk at suitable temperatures and ferment part of the lactose to lactic acid.

The resulting lactic acid transforms the casein from a water-soluble state to a water-insoluble state. The protein remains water-soluble.

Suitable separating processes are then carried out to remove a large part of the aqueous phase and of the substances dissolved therein. One of the substances dispersed in the milk, namely, casein, is recovered in a relatively high concentration.

That process has the following disadvantages: 1. i-.hereas only one of the substances dispersed in milk is to ba treated and recovered, all other substances dispersed in the milk must be processed too. 2. Whey proteins, which are of high biological value, cannot ba recovered. 3. The process requires expensive equipment and a high energy consumption because all dispersed substances must initially be processed. 4. The process pollutes the environment because the whey must ba disposed of.

In view of these disadvantages, thermal pretreating processes or additional processes have bean proposed, which have been disclosed in German Opened Applications 27 23 105, 25 03 340 and 25 45 347 and serve to increase the content of the valuable whey proteins in the curd.

Other processes, which have been disclosed in German Patent Publication 20 65 974 and in British Patent Specification 1,493,437 and in which the protein content of the sweet milk is increased by suitable separating processes, such as ultrafiltration or ultrafiltration and washing, whereafter the milk is soured and/or treated a fc, with enzymes and a coupling product is not obtained.

In the other processes, described in German Opened Applications 27 45 535 and 22 11 737, sour milk or partly soured milk is subjected to ultrafiltration or washed with water during ultrafiltration. The milk may be evaporated before or after the ultrafiltration.

It is an object of all these processes to increase the protein content in relation to the contents of the other substances dispersed in the milk because it is believed that the remaining dispersed contents will reduce the quality of the end product.

All these processes have the disadvantage that uncontrolled changes of the proportions are effected regardless of the changes of states of equilibrium and without an alteration of the microstructures of dispersed substances.

For instance, preconcentrated milk can be used but a specific concentration has not been stated, or the water can be removed after the ultrafiltration regardless of previous drastic changes of properties of dispersed substances.

All these processes result in a formation of bitter substances and in undesired jelly structures, in poor hydrophilic properties and in a product which quickly deteriorates in sensorial qualities.

It has been found that these undesired results are due to the uncontrolled changes of the microstructures of the dispersed substances rather than to the proportions thereof.

For this reason, known separating processes are 30 used in accordance with the invention in order to effect 5323 6 a controlled alteration of the microstructures of the dispersed substances rather than for a mere change of the proportions of dispersed substances.

Xt has been found that any alteration of structure will result also in a change in properties.

By tha use of systematic, controlled separating processes in accordance with the invention, controlled, desirable changes in properties can be effected in accordance with the invention.

It has bean found that, e.g., a bitter taste is due to a hydrophobic property of dispersed substances.

For instance, an indiscriminate preconcentration of milk by an evaporation of water before ultrafiltration will result in a deficiency of water for all dispersed substances, which are present in a water-soluble form. As a result, the structures of all dispersed substances will be altered. For instance, casein combines with salts and lactose, highly hydrophilic substances are bound. The surface area of casein is increased; the water require20 ment is reduced.

When that indiscriminate removal of water and uncontrolled alteration of structure is succeeded by an indiscriminate ultrafiltration, water as well as lactose and salts dissolved in said water will be removed from the milk The remaining protein concentrate will assume a new, uncontrolled equilibrium owing to the presence of an excessive quantity of water so that structures will disintegrate in an uncontrolled manner and hydrophobic properties will become effective and will result in hydrophobic conglomerates so that the end product will have a butter taste.

That undesired change in properties will be increased if water is added during the ultrafiltration in order to increase the protein content relative to the contents of the other dispersed substances.

If an indiscriminate ultrafiltration is succeeded by a removal of water to obtain a final concentrate having a required solids content, the protein structure will disintegrate as has been described hereinbefore.

The previously latent hydrophobic properties are activated and now repel water. Whereas a subsequent removal of water regardless of the microstructuras which are present will result in a rebuilding of certain protein structures, highly hydrophobic structures can no longer be encapsulated. The resulting products have also a strongly bitter taste.

The solubility of salts will be improved by a presouring or partial prasouring of milk. Salts which have been combined with proteins are removed from such compounds. A subsequent ultrafiltration will increase the salt content of the filtrate. This results in an uncontrolled disintegration of the protein microstructures with a risk of a development of hydrophobic properties.

An indiscriminate removal of water before or after ultrafiltration results in undesired influences on microstructures. Tie souring serves only to change the proportions of dispersed substances.

Any processes which serves only to change the proportions of disabled substances will inevitably result in uncontrolled and uncontrollable changes of the structures of dispersed substances, i.e., in entirely uncontrolled an uncontrollable changes of the properties of the dispersed substances sa that a controlled end product cannot be obtained in this manner.

The invention as defined above will now be further explained with reference to the production of fresh cheese and cheese. It will be pointed out that by the selective use of known separating processes as defined above, microstructures can be influenced that a development of hydrophobic properties resulting in a formation of bitter substances will be avoided.

A) Milk or the like, which may ba provided with any additives that may be required, is evaporated to remove about 10 % water. Very little energy is required for such evaporation. The protein microstructures ara increased in size. The structures of the salts and of lactose are so altered that they can be dissolved in less water. The resulting structures permit a succeeding ultrafiltration to be carried out with an optimum efficiency of the ultrafiltration plant because there is no danger that the altered microstructures may clog the membranes.

By the ultrafiltration, the microstructures are altered so that the protein particles have a smaller, but uniform size. For this reason the retentate discharged from the ultrafiltration plant is immediately evaporated once more. As a result, protein structures have a uniform small size are uniformly increased in size. (The first evaporation has resulted in a non-uniform increase in size of the protein structures.) The protein concentrate discharged from the evaporating process is subjected to another ultrafiltration process until the composition has been obtained which corresponds to an optimum cheese jelly structure.

Compared to the state of the art, that procedure affords the substantial advantage that all separating processes are carried out in the range of optimum efficiency, so that considerable energy can be saved, the quantity of permeate which becomes available is decreased by one-half or two-thirds compared with the conventional technology, and the sizes of the protein structures can be so controlled that a succeeding souring or rennet process will result in a jelly which is ideal for the type of cheese to be made.

In a special embodiment of the process, an overconcentration may be effected because all separating processes are carried out at optimum efficiency so that that portion of the permeate which becomes available in such operations can ba cycled and no polluting liquid is to be disposed of.

Any permeate which becomes available can be electrodialyzed in that the salts of the permeate are introduced into the concentrate before the last evaporating step. This practice affords the advantages that the entire salt content remains in the cheese and that the buffering capacity of the concentrate and the microstructure of the protein can be adjusted to suit specific types of cheese.

Such procedures permit the preparation of partial or high concentrates for an end product consisting of soft cheese, cutable cheese or hard cheese. This is not possible in the state of the art. 3236 In such processes the acid and salt contents which are required in the cheese of the type desired can be adjusted in the liquid raw product (concentrate)«, Such concentrate contains the dispersed substances in same proportions and structures as in the finished cheese but still in a water-soluble state.

This concentrate is then transformed from a liquid state to a semisolid or cuttable state in a single process step, e.g,, by an enzymatic process, so that the process steps previously required, which are complicated and time-, material- and energy-consuming and pollute the environment, are entirely eliminated.

The procedures according to the invention as defined above can be applied to the production of all milk products which can be made. In the production of a given milk product, the micro- and macrostructures and the states of equilibrium which are required in the end product are ascertained first and these conditions are then adjusted in the liquid starting raw material by separating processes carried out in series or parallel. In the preparation of some products, liquids which have been separated are added during the process or at the end of the process in an unchanged or changed form and additional quantities may also be added in controlled proportions if this is necessary to form required microstructures.

Individual fractions which become available in the separating processes and may consist of whey proteins, lactose, salts of milk, lactic acid, water etc. may ba subjected to a separate treatment, for instance, a temperature treatment, a further saparation, a separate structure22 > 3 2 3 C> changing treatment, etc. and may then be processed separately or be added to the starting raw material at the same or different temperatures.

B) 10,000 liters milk are subjected to separating processes for altering the microstruetures. The milk contains 9.0 S solids and 91 % water.

Polydisperse protein structures are contained in the water. a) First Separating Treatment 2000 liters milk are treated at a temperature below 65° C for a removal of water by reverse osmosis or evaporation until a water content of 88 % and a solids content of 12 % have been obtained.

This treatment changes the protein microstructures, which adapt to the lower water content. The proteins increase in adaptation to the lower water content.

Without additional measures, these structures would become hydrophobic in a souring process in which substances having a high water requirement (lactic acid) are formed or added. b) First Dilution For this reason the resulting concentrate is diluted with additional 2000 liters milk. 2000 liters milk containing 12 % solids and 88 % water diluted at a temperature below 65° C with 2000 liters milk containing 9 % solids and 91 % water.

The resulting mixture of 4000 liters milk contains 10.5 % solids and 89 % water.

The largest casein structures present disintegrate , i to form some?;hat smaller structures. Casein structures of ; S3 2 3 β medium and small size are not affected.

The smallest casein structures in the starting milk are increased to an intermediate size.

The separating and mixing steps result in more uniform casein structures without a development of hydrophobic properties.

The protein structures of the resulting system are not sufficiently stable in a souring process. c) Second Separating Treatment The mixture described above, which contains .5 δ solids and 39 % water, is now subjected to ultrafiltration at a temperature below 55° C, preferably 60° C, until the concentrate contains more than 11 S, preferably 13.55 % protein.

A concentrate is obtained in an amount of 1333 liters and contains 13.55 % protein, 21 5 total solids and 79 S water. Tha permeate contains 7.S δ solids and 92.4 δ water.

Tha removal of salt and lactose at the beginning' of the ultrafiltration results in a disintegration of the largest casein structures present to structures Of intermediate size. The smallest casein structures which are present agglomerate to form larger structures.

It is apparent that the second separating treatment results in still more uniform protein structures.

But owing to the shortage of water, a succeeding souring process would still give rise to hydrophobic properties. d) Second dilution 1333 liters concentrate are diluted at a temperature below S5° C, preferably 60° C with the remaining GOOO liters starting milk. Tha resulting mixture has a protein content of more than 5 δ, preferably 5.25 -5, a solids content of 11.2 %, and a water content of 38.8 %.

As a result of the separating processes and diluting steps carried out, the initially polydisperse protein structures have been transformed to substantially monodispersa structures.

The substantially monodispersa protein structures must be further stabilized. This is effected as follows: e) Third Separating Treatment 7333 liters of the mixture obtained in step d) are subjected at 60° C to another separating process, such as an ultrafiltration.

The resulting concentrate amounting to 3030 liters contains 12.5 protein, 13 δ total solids and 82 δ water.

This concentrate contains stabilized, substantially monodisparse protein structures which even in a succeeding microbial souring processes or after an addition of acid will noc give rise to hydrophobic properties.

The aroma can be further improved by a moderate, f) Third Dilution with starting milk to a final water content above 82.oo S, preferably S2.3 5. 3030 liters concentrate containing 32 δ water are diluted with 500 liters starting milk to obtain a final water content of 32.23 δ.

That final concentrate is excellently suitable for tha production of curd.

The protein structures thus obtained can be further stabilized in that the final concentrate is heated above S5° C and held at the resulting temperature for more than 2 minutes, preferably 7 minutes. 3 a5 ό Such concentrates may also he used for the production of soft cheese, cuttable cheese or hard cheese.

In ordar to obtain microstructures having the required properties in an aqueous dispersion, the quantity of milk used as a diluent in the third dilution should amount to at least one-half of the quantity of the concentrate to be diluted. 3080 liters concentrate which contain 12.5 S protein and have a solids content of 18 5 and a water 10 content of 32 % are diluted with at least 1540 liters milk which contains 3.4 % protein, 9 % total solids and 91 % water.

The resulting mixture amounts to 4620 liters and contains 9.46 % protein, 15 % total solids and 85 % water.

That mixture is subjected to another separating treatment (ultrafiltration) to obtain 2300 liters of a concentrate which contains 18.9 % protein, 24.4 % total solids and 75.6 % water.

This concentrate is diluted with twice its 20 quantity of starting milk. 2300 liters concentrate + 4600 liters milk = 6900 liters of a mixture containing 8.56 % protein, 14.13 % total solids and 85.87 % water.

This mixture is subjected to ultrafiltration at a temperature of 55° C.

The resulting concentrate amounting to 2750 liters contains 21.5 % protein, 26.5 % total solids and 73.5 % water.

The properties of the microstructuras of the dispersed substances of said concentrate in a water-soluble state will not be adversely affected by an enzymatic treatment and by souring and salting processes.

S3236 The concentrates can be mixed with cream or cream powder, particularly for the production of fatty cheese.

The properties of the protein structures can be improved, particularly for the production of cuttabla cheese and hard' cheese, if the last separating process is succeeded by a removal of water to a water content which is 2-5 % lower than the legally prescribed water content.

It will be particularly desirable to effect before 10 the last separating process a moderate dilution with milk and/or a protein solution and/or a whey protein solution. The diluent used may also contain fat. 2750 liters concentrate containing 21.5 % protein, 26.5 % total solids and 73.5 % water are mixed with at least 500 liters of protein solution containing about 6 % protein, about 7 % total solids and 93 % vzater.

The resulting mixture amounts to 3250 liters and contains 19.12 % protein, 23.5 % total solids and 76.5 % water. Water is then removed from the resulting mixture until it has a water content of about 50 %.

From such a concentrate in which the dispersed substances, particularly the proteins, have substantially monodisperse structures, water can be removed without a deterioration of said structures. Succeeding enzymatic processes will be effected in the range of optimum activity and will not result in a deterioration, particularly in an activation of hydrophobic properties.

If such concentrate is to be aromatized immediately in a sweet range (pH value 6 to S.8), e.g., by salting, the permeate which becomes available is - 27 5 3 2 3 6 subjected to electrodialysis and the resulting brine is concentrated and added to the concentrate.

The water-soluble microstructures thus obtained can be used in a desirable process of producing, e.g., cheese.

By an addition of culture concentrates or edible acids, the final concentrate is adjusted to a pK value which is required for the desired cheese, e.g., 4.7 for soft cheese, 5.1 for cuttable cheese or 5.4 for hard cheese.

The protein structures which are present will not permit a formation of gel by this treatment.

The required salt content of, e.g., 2 to 5 %, is than adjusted, microorganism cultures and/or enzymes are admixed, and the concentrate, which is still liquid, is filled into containers.

The cheese will then coagulate and fully ripen in the packages.

This constitutes an entirely continuous process 20 of producing cheese. fc (¼ ,-· «·« <·» *, «J ο 3) Production of Sour Milk Products Sour milk products are distinguished by the nature of the jelly structure of protein. In their production, protein is transformed from microstructures to macrostructures. These jelly structures must be strongly hydrophilic. For this purpose, their voids must be as small as possible so that they contain no interstitial water. In an ideal jelly structure for sour milk products, water is chemically combined or contained in capillaries.

In the process according to the invention the formation of such a jelly structure can be influenced in that the milk is treated to alter the microstructure of the dispersed substances.

Milk is first evaporated. As a result of this removal of water, the structures of the dispersed substances adapt to the reduced water content. Salts are incorporated in protein structures. Protein particles increase in size although the polydisperse state is maintained, with larger particle sizes.

The ratio of ionodisparsa salts and of salts combined with proteins is changed toward the latter. The form in which lactose is dissolved in water is changed too.

The resulting state is by no means suitable for the formation of the jelly structure described above.

For this reason another separating process, e.g., an ultrafiltration, is carried out in accordance with the invention.

This separating process results in more uniform protein structures although this is effected in another size range than in the previously described process of S3 i. 3 6 producing certified milk. The resulting protein structures are smaller than those in certified milk so that their surface area is larger than in the starting milk.

Ideal conditions are thus obtained for the formation of the above-described gel structures in a subsequent souring process. Such ideal conditions cannot be obtained by processes known in the art.

With the controlled microstructures obtained according to the invention, the solids content can be lower than in the starting milk so that it is possible to add not only the previously separated liquid but additional liquid, e.g., in the form of whey or ultrafiltrate or the like. There will be no pollution of the environment by coupling products.

In a special embodiment of tire process, the permeate which becomes available is subjected to ion exchange or electrodialysis and is then added to the starting material as a buffer or as a lactose concentrate (which may contain dissociation products of lactose). e) Production of Fresh Cheese Fresh cheese has a gel structure which permits part of the original liquid content to be removed but retains the remaining water. In the prior art, water is removed in the required amount only after the gel has . formed or water is removed from the milk by ultrafiltration, which may ba combined with washing, and partial or high concentrates are produced.

These processes have substantial disadvantages.

In none of these processes is the formation of a satisfactory jelly ensured. 5323G In the first-mentioned process the nature of the resulting jelly structures and of the souring sequences cannot be controlled. These processes often result in a fresh cheese which is too dry or which loses water and for this reason has an unsatisfactory aroma and is not sufficiently stable.

In the process involving a removal of filtrate, possibly in combination with washing, more uniform protein structures are obtained but this is effected in a very unfavorable size range so that the finished product contains sand- or gritlike structures and bitter substances.

These serious disadvantages are eliminated by the process according to the invention in that the starting milk is treated first, e.g., by evaporation. The following changes are effected: Starting Milk Composition of Milk After Removal of Water Water content 91.00 % Water content 88,00 % Protein content 3.40 % Protein content 4.53 % Lactose content 4.70 Lactose content 6.27 % Salt content 0.83 § Salt content 1,18 % Fat content 0.02 e. Ό Fat content 0.03 % The protein structures have polydisperse sizes but the protein structures are increased in size.

During the subsequent souring processes, the salt content of the milk is of essential significance for buffering. For this reason the salt content was adjusted so that this buffering capacity is substantially preserved in a succeeding ultrafiltration.

The removal of water is succeeded fay ultrafiltration, which may result in a high concentrate, although all intermediate states are possible. The high concentrate obtained, a.g., by ultrafiltration, has the following composition: Water content 81,27 % Protein content 11.25 % Lactose content 6.27 % Salt content 1.14 % Fat content 0.07 % In this process, the total solids content after the second separating process amounts to 18.73 %; this corresponds to the solids content of fresh cheese.

The process according to the invention permits· the formation of jelly structures which in low concentrates permit a controlled removal of water and in high concentrates ensures that the souring processes will proceed in an exactly controlled manner and will not permit a formation of bitter substances or of sandy, granular structures because the requirements for the formation of an optimum jelly for fresh cheese have been met in the starting system while the water-soluble state has been preserved.

Geliy structures having an even more exactly predetermined consistency and buffering capacity can be obtained in that the ultrafiltrate is subjected to electrodialysis so that the salts contained in the ultrafiltrate are transferred into the low or high concentrates and the final product contains all salts originally contained in the milk or more than the original salt content of the milk (if the quantity of ultrafiltrate subjected to dialysis is increased). - 32 53236 This cannot be achieved by any of the conventional processes, in which a major part of the salts are removed or even washed out.

) Elimination of Undesired Properties in Original Polydisperse Aqueous Systems and Preparation of the System for the Production of Sour Milk Products.

By environmental influences, by an improper treatment and by influences of tha food eaten by the animals, substances dispersed in original polydisperse aqueous systems may be changed in such a manner that it is difficult or inpossible to properly manufacture a product.

All such non-original constituents are dissolved in water and combined with original dispersed substances dissolved in water.

For instance, certain inhibitors are known, which in the production of foods that are to be soured by microbes interfere with or entirely inhibit the action of microorganisms. Such aqueous polydisperse systems give rise to high economic damage.

For this reason the Invention as applied, for instance, to systems which contain inhibitors proposes that the microstructures of the dispersed substances which are originally present and have been altered by inhibitors should be influenced by separating processes in such a manner that the effects of undesired changes in properties will be eliminated and required properties will ba prepared at tha same tima.

A portion of an inhibitor-containing milk is 33238 ultrafiltered at a temperature above 55° c, particularly 30° Co Part of the liquid which is discharged, particularly 50 % of the separated liquid which is discharged, is immediately added to the concentrate formed in the second stage of an ultrafiltration plant.

That operation results in an alteration of the raicrostructures of casein and protein and a liberation into the aqueous phase of inhibitors which ware combined with the original structures.

A major part of the now water-soluble inhibitors contained in the second mixture are removed in the second stage and are included in ths permeate which is discharged. Part of the retentate obtained together with starting milk that has been diluted with water (at least 9 parts of milk to 1 part of water) is supplied to the first stage of the ultrafiltration plant and is ultrafiltrated once more so that raicrostructures of dispersed milk substances which are free from inhibitors ara continuously recovered in the discharged part of ths retentate and the deranged microstructures which hava not yet bean treated are regenerated continuously.

As a result, the raicrostructures of ths dispersed substances contained in the discharged part of the retentate are already in a state which corresponds to original states.

Obviously such a regeneration can also ba carried out when the starting raw material contains other nonoriginal water-soluble dispersed substances, e.g., from the environment.

The regenerated part is now to be processed further to obtain sour milk products.

Sour milk products depend on gel-forming properties, e.g., of dispersed milk substances. It is important that the gel is not formed in an uncontrolled manner at random but a jelly is formed which contains little void water and much capillary water and particularly hydrate water.

For this reason the water-soluble microetructures must be prepared for the development of the gel-forming property of protein. This has not been possible in accordance with the state of tha art.

For this reason it is proposed by the invention to devide, e.g., the milk having microstructures which have bean corrected by the process described above. At least 20 % of the milk to be processed is subjected to a process by which water is removed. 10 ΐ of the water content are removed at temperatures below u5° C or preferably at 65° C.

Additional 20 δ of the milk to be processed are ultrafiltered at the same time. Tha ultrafiltration is continued until 80 % retentate and 20 % permate have formed. The product from which water has bean removed is then mixed with the retentate obtained by ultrafiltration.

The mixture is ultrafiltered once more at a temperature οίδί5 C. During the ultrafiltration of the mixture, tha remainder of the pretraated milk at a temperature of 65° C is continuously fed to the ultrafiltration so that the final concentrate contains at least 12 % solids.

The milk which has thus been treated is free from 30 inhibitors and has protein microstructures which are water-solubla and permit the formation of an optimum jelly. 6) Processing of Recombined Systems Recombined systems are systems which have been recovered in that substances which have been dried, for instance, are redissolved.

Procedure; Milk powder and/or protein powder of animal or vegetable origin are mixed with water to form an aqueous polydisperse system. Approved additives, such as salts, binders, enzymes, sweetening agents etc., which are required may be admixed. Because the states of solution in such a system are mainly obtained at random, it is vary difficult to process the system so as to form products.

For this reason the invention provides that such a random aqueous system is treated to form concentrate which has controlled microstructures and can be processed further. 1000 liters of a recombined starting solution are first hyperfiltered at a temperature below 20° C, mainly 15° C, until about 10 % of the carrier liquid have been removed.

One-half of the concentrate is then mixed with additional 1000 liters of the recombined starting liquid and the mixture is ultrafiltered at 55° C until 800 liters concentrate have been obtained.

During the ultrafiltration, the remainder left after the hyparfiltration is continuously supplied to the ultrafiltration.

The concentrate which becomes available is mixed with the carrier liquid obtained by the hyperfiltration. The resulting concentrate can then be processed further to form, e.g,, evaporated or sterile milk. In this special case the permeate discharged from the ultrafiltration step is electrodialyzed and the resulting liquid, which is substantially free from salts, is admixed to the concentrate that is to be processed further to obtain evaporated or sterile milk.

The product now obtained is excellently suitable for making evaporated or sterile milk without an occurrence of Halliard reactions or a precipitation of proteins and without a tendency to thicken subsequently.

Claims (6)

1. A process for increasing the uniformity in the structure of proteins in milk wherein a) a partial amount of the milk is preconcentrated by 5 ultrafiltration to at least one and a half times the value of the protein content, h) the preconcentrate obtained is mixed with the remainder of the milk, c) the mixture obtained is concentrated by ultrafiltration to at 10 least one and a half times the value of the protein content, d) a part of the water is extracted from the concentrate obtained by evaporation under vacuum or reverse osmosis at a temperature below 65°C, e) the concentrate obtained is subjected to a further ultrafiltration, f) the concentrate obtained is mixed hack with the water obtained 15 in step d), g) the mixture obtained in step f) and the filtrate obtained from the ultrafiltrations are each subjected to a heat treatment at up to 85°C, and h) the two phases from step g) are mixed.

2. A process according to claim 1, wherein the process is carried out using different temperatures for the individual separating 20 processes and/or the adding hack of fluids at different temperatures.

3. A process according to claim 1 or 2, wherein the mixing is carried out continuously while separating processes are running. - 38 5 3 2 3S

4. A process according to claims 1-3, wherein added substances are added before a separating process, during a mixing process, 25 during a separating process or after a separating process.

5. A process for increasing the uniformity of the structure of milk proteins substantially as described herein by way of Example.

6. Milk products processed in accordance with any of the preceding claims.