CH634969A5 - PROCESS FOR RECOVERING MILK PROTEINS. - Google Patents

Description

The present invention relates to a process for recovering milk proteins.

Traditional processes for recovering or separating proteins from milk use technologies based on the coagulation of casein, using for example animal or microbial rennet, or by biological or chemical acidification. These methods have the drawbacks mentioned below:

- non-retention of serum proteins and usually loss of these;

- presence of acid residues;

- highly polluting by-products (small milks);

- difficult recovery of these by-products (small acid milk for example);

- often unpleasant taste of caseins, after drying;

- difficulty in handling caseins after coagulation.

Other methods consist in separating proteins from the other constituents of milk by ultrafiltration, these proteins then being recovered in the state in which they are found in milk, that is to say in the undenatured state. This last characteristic introduces significant constraints at the level of the conduct of the ultrafiltration which is seen limited to small flow rates, to small temperature ranges and exposed to risks of clogging, in short to relatively modest yields. In addition, the ultrafiltration membranes must be washed very frequently.

The method according to the invention has the consequence of circumventing these difficulties while providing considerable and unexpected advantages. According to this method, a milk is subjected to a heat treatment allowing a partial denaturation of the proteins which it contains, these are separated from the other non-fatty constituents of the milk by ultrafiltration, said proteins being found in the retentate fraction, then one makes undergo additional heat denaturation of proteins in the retentate.

In other words, the method according to the invention is characterized by a series of three operations:

a) heat treatment of milk, skimmed or whole, preconcentrated if desired, thermally, by ultrafiltration or by hyperfiltration, this milk can be reconstitution milk,

b) ultrafiltration of the milk thus treated,

c) heat treatment of the retentate obtained.

To simplify the rest of the presentation, and having regard to the thermal effect on proteins, these three operations will be designated respectively by a: predenaturation, b: ultrafiltration and c: post-denaturation.

Prenaturation of proteins, caused by heat, can be accomplished in various ways, for example at high temperature between 100 and 180 ° C for 5 s to 2 min or at lower temperature between 85 and 100 ° C for 10 s to 50 min, denaturation rates varying between 20 and 60%.

It has been noted that the predenaturation has the consequence of precipitating the heat-sensitive proteins and of fixing them on the micelles of casein, which considerably reduces their sensitivity to subsequent technological treatments, drying for example, and saves their nutritional quality (inhibition of the reaction of Maillard).

The ultrafiltration operation can be carried out, as is well known, in a closed circuit, by means of a buffer tank in which the retentate is recycled. It can also be carried out using several membranes or ultrafiltration modules arranged in series. The protein content of milk rises gradually, up to, for example, a content of 10 to 13% and if desired up to 25%, a content which can be reached without major difficulties. The content of the other constituents of the milk remaining unchanged, that is to say that the relative proportion of proteins has been greatly increased. If it is desired to recover proteins whose residual content of lactose and mineral salts is reduced in absolute value, the retentate is diluted during ultrafiltration.

This ultrafiltration technique with simultaneous dilution is sometimes called diafiltration. The diluting agent, essentially water, acidified water or whey, is added to the buffer tank, or between two successive ultrafiltration modules.

The temperature at which the ultrafiltration is carried out can be freely chosen, especially since the milk proteins having already been heat treated, there is little to fear from harmful influences of heat on them. For reasons related both to obtaining high ultrafiltration rates (high permeation rates) and bacteriological safety, it is advantageously ultrafiltered at a temperature between 50 and 90 ° C.

Post-denaturation of proteins by heat, applied to the retentate, can be carried out in the same way as pre-denaturation, for example at high temperature between 100 and 180 ° C for 5 s at 20 min or at lower temperature between 85 and 100 ° C for 10 s to 50 min.

The conditions of the heat treatments of pre- and post-denaturation can be crossed, for example predenaturation 100 to 180 ° C, 5 s to 2 min and post-denaturation 85 to 100 ° C, 10 s to 50 min or even predenaturation 85 to 100 ° C, 10 s to 2 min and post-denaturation 100 to 180 ° C, 5 s to 20 min. We have also found that

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the denaturation rate obtained by post-denaturation is, under equal conditions, higher as a result of the lower content of lactose in the treated product, lactose which plays a protective anti-denaturing role with respect to proteins. In addition, a low lactose content means a low risk of a Maillard reaction.

The total denaturation rates resulting from the combination of predenaturation and post-denaturation after ultrafiltration can be very high and close to the theoretical maximum possible (of the order of 95%).

In terms of the advantages of the method according to the invention, the following elements can be listed:

- ease of processing whole milks, which industrially are always very delicate to ultrafiltrate, the ultrafiltration being able to be carried out at higher temperature and higher flow rate;

- direct recovery of all milk proteins;

- better reduction of the microbial population of the proteins collected, due to the double heat treatment of denaturation and post-denaturation;

- better protection of lysine, which is an essential factor in nutritional value;

- softer overall treatment compared to a one-step treatment, post-denaturation being more effective under equal conditions or requiring milder conditions by equal effectiveness;

- higher permeation rates (therefore yields), from 80 to 400%, than practicable permeation rates when the milk proteins are not predenatured.

According to a preferred embodiment of the process according to the invention, the proteins of whole or skimmed milk are denatured by heat treatment at 95-100 ° C. for 10 to 30 min, either in a heat exchanger, either by steam injection and storage in a tank, or at 120-160 ° C for 10 s to 2 min, either in a heat exchanger, or by direct steam injection with waiting in tube.

The milk thus treated is then ultrafiltered at a temperature between 55 and 75 ° C. If necessary, the retentate is diluted with water during ultrafiltration, or with acidified water or whey. The retentate is then subjected to a post-denaturation heat treatment, identical to or different from the heat treatment applied to the starting milk before ultrafiltration.

The proteins obtained which can be dried are distinguished by their high quality and by a composition which can vary within very large limits depending on the denaturation mode and the type of ultrafiltration used. In particular, proteins can be obtained whose residual lactose and salt contents are remarkably low. These proteins naturally find their use in dietetics, especially in infant dietetics. Information on this will be given in the examples which follow, in which the percentages are expressed in weight value and on the basis of dry matter.

Example 1:

A skimmed milk having undergone a predenaturation heat treatment at 95 ° C. for 10 s, then cooled to 55 ° C., is passed through an ABCOR ultrafiltration module equipped with HFM 180 SG membranes. The ultrafiltration is continued until a concentration ratio of 3 times is obtained. Under these conditions, the ultrafiltration rate (treated product expressed in l / m2 / h) is 50 l / m2 / h with a protein / lactose ratio of the order of 2.

A new post-denaturation heat treatment is then applied at 140 ° C for 60 s. A retentate is obtained with the following composition:

dry matter 14.14%

total nitrogen 1.26%

0.24% non-caseic nitrogen

lactose 4.26%

ash 1.10%

0.21% calcium

It is also noted that after the predenaturation, the percentage of denatured proteins on the total proteins is 25. Post-denaturation brings this denaturation to 90%.

Comparative example:

A skimmed milk is passed without predenaturation on an ABCOR module, equipped with HFM 180 SG membranes at a temperature of 55 ° C. After 3 hours of walking, the ultrafiltration flow is less than 30 l / m2 / h.

Example 2:

Whole milk is passed, after predenaturation heat treatment at 115 ° C for 10 s, cooled to 75 ° C, through a UF ABCOR module equipped with HFM 180 SG membranes.

The ultrafiltration is continued until a concentration ratio of 2.5 times. Under these conditions, the ultrafiltration flow rate is 60 l / m2 / h with a protein / lactose ratio of 1.4.

A new post-denaturation heat treatment is then carried out at 95 ° C. for 30 min.

After the first denaturation, 22% of denatured proteins are obtained out of total proteins. Post-denaturation brings this denaturation to 92%.

Comparative example:

Whole milk is passed without predenaturation on an ABCOR module, equipped with HFM 180 SG membranes at a temperature of 75 ° C. After 2 h of operation, the ultrafiltration flow is less than 15 l / m2 / h.

Example 3:

A skimmed milk having undergone a predenaturation heat treatment at 120 ° C. for 10 s, then cooled to 55 ° C., is passed through an ABCOR ultrafiltration module equipped with HFM 180 SG membranes. The volume is reduced 3 times, then the retentate is diluted with water while feeding with water in an amount equal to the permeate removed.

The ultrafiltration / diafiltration flow rate is 33 l / m2 / h and the retentate obtained after diafiltration has a protein / lactose ratio of 6.45.

Or then proceeds to post-denaturation at 110 ° C for 10 s, which gives a denaturation rate of 91%, the composition being established as follows:

dry matter

10.50%

total nitrogen

1.27%

non caseic nitrogen

0.20%

lactose

1.26%

ashes

0.78%

calcium

0.18%

Comparative example:

The procedure is as for Example 3 but without pre-denaturation. An ultrafiltration / diafiltration flow rate of only 19 l / m2 / h is obtained.

Example 4:

The procedure is as described in Example 3 but diluted (diafilter) with water acidified with lactic acid, keeping the pH of the retentate constant at 6.00. A retentate is then obtained to which a heat treatment is applied at 95 ° C for 10 s. The product obtained, which has the following composition:

dry matter 10.60%

total nitrogen 1.29%

0.21% non-caseic nitrogen

lactose 1.17%

ash 0.65%

0.12% calcium

is partially decalcified. It has a protein / lactose ratio of 7.05 for a denaturation rate of 90%.

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Example 5:

The procedure is as in Example 3, but diluted (diafilter) with a denatured sweet whey containing 6% dry matter. 2000 ml of starting milk is diafiltered with 23001 whey, the concentration ratio being 3. After post-denaturation, as indicated in this example 3, a retentate is obtained with a casein / lactalbu-mine ratio of 2.

The protein / lactose ratio is 1.93.

Example 6:

Milk having a dry matter content of 10% is reconstituted from skimmed-milk powder and water. Denaturation is carried out at 95 ° C for 10 s. It is cooled to 55 ° C. and it is passed through an ABCOR ultrafiltration module, HFM 180 SG membranes. The concentration is continued until a volume reduction of 3 times. Under these conditions, the ultrafiltration flow rate is 61 l / m2 / h, with a protein / lactose ratio of 2 in the retentate.

A post-denaturation is then carried out at 140 ° C. for 60 sec and a denaturation rate of 93% is obtained.

Example 7:

A milk is reconstituted from water and a milk powder which has undergone during its preparation a denaturing treatment corresponding to the heat treatment of predenaturation. We then continue as described in Example 6 with regard to ultrafiltration and post-denaturation and we obtain a final product very similar to the product of this example.

Example 8:

Skim milk is concentrated by hyperfiltration to a dry matter content of 20%. A concentrate (10001) is obtained which is heat treated at 95 ° C. for 10 s, then it is directly diafiltered at 55 JC with 15001 of water, keeping the level constant.

The protein / lactose ratio obtained is 1.2, the ultrafiltration rate being 26 l / m2 / h.

Post-denaturation is then carried out at 140 C for 60 s, which gives a denaturation rate of 91%.

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Example 9:

The product obtained in Example 4 is, after adjusting the pH to 5.2 and standardization in fat, spray-dried. The powder obtained has interesting characteristics; in particular, io after hot reconstitution, it gives a stringy and stringy texture and can advantageously replace cheese of the Mozzarella type.

Example 10:

An infant dietetic product is prepared by mixing wheat flour, sucrose, vegetable oil and the product of Example 1.

The pasty mixture is then dried on rolls and a product is obtained which has a remarkable nutritional value and constitutes an excellent weaning flour.

The level of available lysine is high, the measured value being 4.2%, expressed as a lysine / total protein ratio.

Example 11:

Whole milk having been subjected to a 2S heat treatment of 115 ° C. for 10 seconds, then cooled to 65 ° C., is passed through an ultrafiltration module until a volume reduction of 2.5 times. A new heat treatment of 95 ° C. is carried out for 10 s.

The product obtained can be used as it is in the manufacture of cheeses, in particular cheeses of the soft paste type (Brie, Camem-30 bert, etc.). It can also be spray-dried and the powder obtained can be added to the milk, during the period of underproduction, in order to standardize and regularize the production.

The cheese yield is clearly increased as a result of good retention of serum proteins.

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Claims (14)

634969 1. Process for separating proteins from milk, characterized in that a milk is subjected to a heat treatment allowing partial denaturation of the proteins which it contains, that these are separated from the other non-fatty constituents of the milk by ultrafiltration, said proteins being found in the retentate fraction, then that the retentate is subjected to an additional heat treatment for denaturing the proteins. 2. Method according to claim 1, characterized in that the milk is a skimmed milk. 2 3. Method according to claim 1, characterized in that the milk is whole milk. 4. Method according to claim 1, characterized in that the milk is a thermally concentrated milk, by ultrafiltration or by hyperfiltration. 5. Method according to claim 1, characterized in that the proteins are separated from the other non-fatty constituents of milk by ultrafiltration with dilution. 6. Method according to claim 5, characterized in that the proteins are separated from the other non-fatty constituents of milk by ultrafiltration with dilution while keeping the volume of the retentate constant. 7. Method according to claim 5, characterized in that the proteins are separated from the other non-fatty constituents of milk by ultrafiltration with dilution with water, acidified water or whey. 8. Method according to claim 1, characterized in that the heat treatment before ultrafiltration is carried out between 100 and 180 ° C for 5 s to 2 min or between 85 and 100 ° C for 10 s to 50 min. 9. Method according to claim 1, characterized in that the heat treatment after ultrafiltration is carried out between 100 and 180 ° C for 5 s to 20 min or between 85 and 100 ° C for 10 s to 50 mins. 10. Method according to claim 1, characterized in that ultrafilter at a temperature between 50 and 90 ° C. 11. Method according to claim 1, characterized in that the proteins are recovered in the dry state, by drying the retentate after heat treatment. 12. Milk proteins, recovered by the process according to claim 1. 13. Use of the milk proteins recovered by the process according to claim 1, as an ingredient in infant and dietetic products. 14. Use of the milk proteins recovered by the process according to claim 1, as an ingredient in the manufacture of cheese.