IE43987B1 - Method for the clarification of liquids containing whey protein - Google Patents

Abstract

1519897 Whey proteins STICHTING BEDRIJVEN VAN HET NEDERLANDS INSTITUT VOOR ZUIVELONDERZOEK 19 Nov 1976 [21 Nov 1975] 48473/76 Heading C3H A method of clarifying a liquid which contains whey protein comprises demineralizing the liquid so as to obtain a liquid having an ash : protein ratio not exceeding 0À08 : 1, adjusting the protein content of the liquid if necessary to a value not exceeding 1À5% by weight, adjusting the pH of the liquid to a value in the range 4À2 to 4À8 without disturbance of the liquid so as to cause sedimentation and separating the sediment under turbulence-free conditions. Examples describe the passage of centrifuged and pasteurized whey from Gouda cheese-making over a cation and anion exchanger successively. The demineralized whey had a pH of 5À1, a protein content of 0À70% by weight, an ash content of 0À03% by weight and a similar fat content. Sedimentation data of such a material are reported and the use of such materials to make drinks, meringues and concentrates.

Description

The invention relates to a method for the clarifio ation of whey-protein-containing liquids.

One of the most important whey-protein-containing liquids is whey, which is obtained in large quantities in the preparation of cheese and casein. Due to the high nutritional value of whey proteins, whey, and particularly a concentrate thereof, is an attractive starting material for food-stuffs. Besides protein, whey also contains milk salts, lactic acid and lactose as well as fatty components and micro-organisms, the latter producing turbidity of the whey and its concentrates .

It is known that the proteins from whey and whey concentrates may be obtained either by ultra-filtration through a molecular sieve or by recovering them by means of forming insoluble complexes thereof with other substances. Solutions of thus obtained proteins are slightly turbid, may form a ring of fatty material on the surface and, moreover, after a certain period of storage in contact with the air, will acquire a poor flavour due to oxidation of fatty materials still present. In Dutch Patent Application 73.11095 it is suggested, therefore, to adjust the pH of ultra-filtered whey, which has optionally been subjected to gel filtration, within the range of from 4.4 to 5.0, to separate the thus formed precipitate by micro-filtration and to isolate the filtrate that contains the soluble protein fraction. A disadvantage of this suggested method is that appropriate equipment is not generally available in dairy plants and that micro-filtration is a time-consuming operation.

We have now found that this disadvantage may be avoided by a method which includes demineralizing the whey-protein-containing liquid to be clarified.

According to the invention, there is provided a method of clarifying a liquid which contains whey protein, which comprises demineralizing said liquid so as to obtain a liquid having an ash:protein ratio not exceeding 0.08:1, adjusting the protein content of the liquid if necessary to a value not exceeding 1.5% by weight, adjusting the pH of the liquid to a value in the range 4.2 to 4.8 without disturbance of the liquid so as to cause sedimentation to occur and separating off the sediment under turbulence-free conditions.

It is preferred that the demineralization adjustment of the protein content and adjustment of the pH are carried out in the order specified.

If required, the clarified liquid may be concentrated, e.g. at a neutral pH value, by means of membrane filtration, in which case the flux is considerably higher than in case of ultra-filtration according to the known method described above. Of course, other methods of concentration, in which the protein is not denatured, may also be used.

Whey-protein-containing liquids which may be clarified according to the invention include sweet and acid whey (including first and/or second whey) produced in the preparation of cheese, cottage-cheese, casein or similar products, the mother liquor remaining upon -4crystall!sation of lactose from concentrated whey, as well as whey concentrates, demineralized whey and solutions of whey powders. Preferably, the whey is thoroughly freed from fat and curd fines and is pasteurized under such conditions that no denaturation of protein has taken place.

In order to reduce the ash content of the liquid to be used to a sufficiently low value, various known demineralization methods may be employed such as:1. demineralizing by means of a cation and anion exchanging resin successively; 2. demineralizing by means of a dialysis or an electrodialysis; 3. gel filtration; 4. ultra-filtration until the required ash-protein ratio is attained in the retentate, followed by renewed dilution with water.

Preferably the ash content is reduced by passing the liquid to be demineralized over an ion exchanger, demineralization being preferably carried out so as to obtain an ash:protein ratio of 0.05:1.

In the method according to the invention, complexes are formed from - probably globulin-like - proteins, fatty substances and bacteria at a pH value close to the iso-electric point of the whey-proteins.

The ash concentration in the liquid is further reduced after demineralization by formation and separation of sediment, whereby substances causing the undesirable turbidity (fatty substances and bacteria) are removed. Some whey-protein may also be removed and it is therefore essential to select conditions in such a manner that as little protein as possible is lost. - 5 but, at the same time, as much fatty materials and bacteria as possible (or their spores) are removed with the sediment. During or after the demineralizing step, the solutions to be clarified should be in the pH range of from 3.5 to 5.5 (preferably 3.5 to 5.0) until sedimentation is desired.

In a number of tests, liquids containing 1% wheyprotein and therefore having various ash/protein ratios were made from various whey-protein solutions obtained by ultra-filtration. The highest degree of flocking was at pH values in the range of from 3.5 to 5.5. After elimination of the flocculate, the transmittance for light of 600 nm in the transparent solution was determined in comparison to that of an empty cuvet (that is, containing air only). (All subsequently mentioned transmittance values were measured in the same way). Solutions having a pH in the range of 4.2 to 4.8 and having an ash content of 0.04 or 0.05% had transmittance exceeding 90%.

These solutions were therefore substantially as clear as water. Thus, the major part of the opacifying substances had been removed with the sediment, yet the protein content had been reduced by only about 10%.

At an ash/protein ratio of 0.08, the transmittance was still about 70%; however, if the ratio exceeded 0.10 (in a method not according to the invention) the transmittance decreased to 50% or less.

After adjustment of the pH in the method according to the invention, the turbidity first increases (formation of complexes) and then decreases (due to sedimentation of the aggregates). This effect is more rapid as the temperature is higher but the final degree of clarification obtained is less at 50°C than at 25°C or at 5°C. This may be due to the fact that, at 50°C, 3987 - 6 the kinetic energy is too high, as a result of which the complexes are somewhat unstable. Consequently, at 50°C, a sufficiently clear solution can not be obtained if sedimentation is allowed to take place simply under the influence of gravity, but such a solution can be obtained by using a centrifuge.

Apart from the pH and the afeh/protein ratio, the protein content of the solution is also critical for proper clarification. If the protein content is more than 2% by weight (in a method not according to the invention) clarification will proceed less favourably than at a protein content of 1% or less. This was verified in a number of tests in which whey was concentrated by ultra-filtration, again diluted to a protein content of 1% by weight and then concentrated again by continued ultra-filtration until protein solutions of 2, and 4% were obtained. In the four protein solutions, the pH value was adjusted to 4.6, upon which a slowly settling flocculate was formed. After 24 hours, the transmittance in the top layer was measured and the fat and protein losses calculated by drawing up a material balance. The results obtained in these tests are given in the following Table A.

Table A Influence on the clarification of the protein content Protein % by weight Ash/ In the top layer after 24 hours' clarification protein % Transmittance % Defatting % 1.05 0.070 78 76 2.00 0.050 29 63 3.04 0.043 10 53 4.00 0.035 3 44 - 7 The protein content is less than 1.5% by weight in the liquid to be clarified in the method according to the invention. A preferred protein content of the liquid to be clarified is in the range 0.5 to 1.5% by weight.

The method according to the invention enables the preparation of clear liquids containing whey protein without the necessity of expensive equipment or equipment which is unusual in dairy plants. The clear liquids obtained may be employed as such as a base for proteinenriched soft drinks or nourishing drinks or be conventionally concentrated (for example by ultra-filtration) or dried optionally after modification of the pH. When the liquid is concentrated by ultra-filtration the flux is far superior than in the case of ultra-filtrating a non-clarified whey.

If desired, the liquid may be pasteurized before being clarified in the method according to the invention. However, a considerable proportion of the bacteria present is eliminated from the whey by sedimentation in the method according to the invention. For example, 1% by weight solution of a demineralized whey-protein powder had a germ count of 24,0(30 per ml, whereas after a night1s clarification at 4°C, the germ count was just 210 per ml.

Not only bacteria but also their spores are eliminated in the method according to the invention, as was demonstrated in an experiment in which spores of B. subtillis were added to a 1% by weight solution of a demineralized whey-protein powder. After acidification to a pH value of 4.6, 740 spores per ml were present. After storage for 1, 3, 6 and 24 hours at 4°C, the number - 8 of spores in the resulting clear liquid was reduced to 12, 6, 3 and 1, respectively. If, on the other hand, the spores were added after clarification, the major part of these spores remained in the clear liquid 24 hours later.

Soft drinks containing about 3% by weight of whey protein obtained from a liquid clarified according to the invention may be pasteurized at least 20 minutes at 70°C at a pH value of from 2.5 to 3.5 without precipitation and turbidity.

The whey protein obtained according to the present invention is not only suitable for use in nourishing drinks but also possesses improved foaming properties.

This is probably due to the fact that foam-inhibiting substances are also eliminated during the clarification.

When, for the purpose of determining the foaming properties, an aqueous solution of 10% by weight whey protein was beaten up at top speed during 5 minutes in a Hobart N 50 (dough) beater and the foam obtained conveyed to a measuring cylinder, the suitability for beating (% increase of volume) of clarified whey-protein was two or three times the increase of volume of nonolarified whey-protein. The foam stability (fraction of the quantity liquid still present in the foam after one hour's standing) was 80 to 100% which was superior to that of non-clarified protein foam. The clarified whey protein may be employed in substitution for hens' egg protein for meringues and other confectionery products.

In order that the invention may be more fully understood, the following Examples are given by way of illustration only.

Example 1 Centrifuged and pasteurized whey - a mixture of first and second whey from Gouda cheese-making - was demineralized by passing it over a cation exchanger and then over an anion exchanger. The demineralized whey thus obtained had a pH of 5.1, a protein content of 0.70% by weight, an ash content of 0.03% by weight and a fat content of 0.03% by weight. A transparent cylinder, which was 1 metre high and had draining tubes fitted at a distance of 15 centimetres from one another and from the bottom respectively, was filled with the demineralized whey, which had a temperature of 5°C, and the pH thereof was adjusted to a value of 4.5. Coarse aggregates formed rapidly, the finer ones took more time to reach the sediment layer. Prom each tube whey samples were taken at intervals, the transmittance of the samples being measured. The depth of the sediment layer was determined at intervals. The results are given in the following Table B, which shows that clarification was substantially complete after 4 hours.

Table B Settling Period (hours) Transmittance of liquid (%) the following depths: at 75cm. Depth of sediment (cm.) 15cm, 30cm. 45cm. 60cm. 1 61 52 42 43 24 8¾ 2 77 69 64 63 66 6¾ 4 83 80 79 80 81 5¾ 6 61 81 82 82 83 5 439®7 - 10 Example II A considerable part of the fat and curd-fines present in first whey from Gouda cheese-making was removed by centrifuging. The centrifuged whey (which had an ash content of 0.48% by weight) was pasteurized and demineralized in the same manner as in Example I.

The demineralized whey issuing from the anion exchanger had a protein content of 0.85% by weight, an ash content of 0.04% by weight and a pH of 5.3. The fat content was 0.07% by weight both before and after demineralization. The pH of the demineralized whey was adjusted to 4.6 and the whey was then pumped into a cylindrical tank which was 3.5 metres high. The flocculate thus formed was allowed to settle at 5°C for 24 hours. Thereupon, a sediment layer with a depth of 0.3 m had formed, from which the clear supernatant liquid was separated. The rate of clarification was calculated to be at least 0.13 m/h. The protein content in the clarified liquid was still 0.75% by weight, about 12% of the protein being lost with the sediment.

On the other hand, the fat content was only 0.003% by weight, so that 95% thereof had been eliminated with the sediment. The protein content of the sediment was 3.26% by weight and the fat content thereof was 0.76% by weight. This sediment could be used as forage.

Example III Portions of the demineralized whey of Example I, the pH of which had been adjusted to 4.6, were passed at 5°C through a sludge centrifuge operating at an acceleration of 4600 g. Due to changes in the flow speed, average residence times in the drum were adjusted between half a minute and four minutes. The protein content and the light transmittance of the clarified whey issuing from the centrifuge were measured. The results are given in the following Table C, from which it can be deduced that the average protein loss was 14%. At longer residence times, the loss is slightly more than at, for instance, 1 minute but at 0.6 minute the whey issuing was still slightly turbid. The germ count of the whey was reduced by clarification from 220,000 to 4,200.

Table C average residence time (min.) 4.0 3.5 1.8 1.5 1.0 0.6 light trans- mittance (%) 86 85 82 84 82 76 protein content (% by weight) 0.60 0.58 0.60 0.60 0.62 0.61 Example IV Centrifuged first cheese whey having a pH of 6.6 was demineralized in a dialysis tube against a tenfold amount of distilled water. In part of the dialysate obtained after 15 hours the pH was adjusted to 4.6.

The resistance of the liquid in a cell between electrodes of 1 cm at a distance of 1 cm had increased from 137 ohms to 2000 ohms; the protein content was 0.85% by weight and the ash content was 0.06% by weight. After standing for 24 hours the clear liquid was siphoned off the settled flocculate. Both this clarified whey and the original, non-dialysed whey were ultra-filtered at pH values of 4.6 and 6.5. The flux was regularly determined and the attained reduction in volume (VR) was noted. The flux of the clarified whey was much higher than the flux of the non-clarified whey, as 43g87 - 12 appears from the accompanying drawing. This was the case at both pH values, both after the same permeation period and at the same volume reduction.

From this example it is clear that, when preparing whey-protein concentrate by means of membrane filtration processes, it is advisable to clarify the whey first and to concentrate the protein afterwards, whereupon a higher filtration output is obtained with less fouling of the membranes.

Example V Whey was concentrated to 95% volume reduction by ultra-filtration. Part of the retentate was further concentrated in a circulation evaporator at 68 to 70°C and then spray-dried at an inlet temperature 175°C and outlet temperature 84°C to form a powder A. The remaining concentrate was diluted to a 1% by weight protein content at an 0.05% by weight ash content and acidified to a pH of 4.6. After allowing the liquid to stand for one night, the clarified liquid was separated and concentrated again to 95% volume reduction by ultra-filtration, to form a “clarified1' powder B.

Powder A (which is comparative) and powder B (which is according to the invention) were each stored in air at 20°C for 10 months and thereupon evaluated as to flavour by a number of expert inspectors. In an evaluation scale ranging from 3 to 8, in which 5 stands for insufficient, 6 for sufficient and 7 for good, the average judgment as to flavour was 5.7 for powder A and 6.9 for powder B. The “non-clarified powder A showed defects in flavour originating from oxidation, while no such defects were found in the clarified powder B.

With both powders, a foaming experiment was carried out as described above. Increase of volume and foaming stability were 1600% and 70% when powder A was used and 3400% and 95% when powder B was used.

Aqueous solutions containing 10% by weight protein were prepared therefrom. A hen's egg protein concentrate (c) containing 10% by weight protein and the above-mentioned 10% solutions were each conventionally beaten with sugar in a ratio of 65 parts by weight of sugar and 20 parts by weight of concentrate A, B or C.

Then the foam was brought into the required form, then keeping it first at a temperature of 125°C for 30 minutes and, finally, it was dried at 100°C for 30 minutes.

The appearance and flavour of meringue prepared with the “clarified whey-protein powder B (according to the invention) could not be distinguished from the corresponding properties of meringue prepared from hen's egg protein concentrate C.

Meringues prepared from the non-clarified wheyprotein A, bulged out into an amorphous mass during baking.

Example VI The powders from Example V were dissolved in water and mixed with an orange concentrate in a conventional manner. Nourishing drinks having protein contents in the range of from 1 to 4% hy weight were obtained which also contained 5% by weight of sugar, 2% by weight of citric acid and 0.1% by weight of sodium benzoate.

The drinks were heated in bottles for 20 minutes up to 70°C, stored at 5°C for three months and then evaluated.

In each bottle containing non-clarified protein A, made as a comparison, protein had separated during heating and had settled out and a ring of fatty components had deposited at the top of the bottles. With these comparative drinks there was a difference in flavour because of oxidation thereof. No difference in flavour had occurred in the bottles containing nourishing drinks prepared from powder B, nor was there any sediment or a ring of fatty substances present at the top.

Example VII The demineralization of the whey, as described in Example II, was further continued. Prom the whey issuing from the anion exchanger, samples were regularly taken, the pH of which samples gradually decreased. Samples with values between 4.0 and 5.2 were stored at 2°C for 24 hours; after 1, 3 and 20 hours the transmittance of the whey samples was measured. In the sample having a pH of 5.2 no clarification took place; the transmittance remained substantially unchanged.

In the other samples, and particularly those having pH values in the range of 4.2 to 4.8, clarification did take place as appears from the transmittance values shown in the following Table D. Each time, before sampling, the transmittance was 2% only.

Table D Transmittance in 1% by weight of wheyprotein solution at pH values of; Storing - period 5.2 5.0 4.8 4.6 4.4 4.2 4.0 1 hour 2 10 36 59 62 59 17 3 hours 2 26 67 80 78 83 33 20 hours 3 40 68 80 84 86 40

Claims (14)

1. CLAIMS:1. A method of clarifying a liquid which contains whey protein, which comprises demineralizing said liquid so as to obtain a liquid having an ash:protein ratio not exceeding 0.08:1, adjusting the protein content of the liquid if necessary to a value not exceeding 1.5% by weight, adjusting the pH of the liquid to a value in the range 4.2 to 4.8 without disturbance of the liquid so as to cause sedimentation to occur and separating off the sediment under turbulence-free conditions.

2. A method according to claim 1, in which the liquid which contains whey protein is whey.

3. A method according to claim 1 or 2, in which demineralization is effected by passing the liquid over an ion-exchanger.

4. A method according to any of claims 1 to 3, in which the ash:protein ratio is not more than 0.05:1.

5. A method according to any of claims 1 to 4, in which said protein content is at least 0.5% by weight.

6. A method according to any of claims 1 to 5, in which the demineralized liquid is stored at a pH outside the range 3.5 to 5.0 before adjusting the pH thereof.

7. A method according to any of claims 1 to 6, in which the sediment is separated off by centrifuging.

8. A method according to claim 7, in which the clarified liquid is further purified by ultra-filtration.

9. A method according to claim 1, substantially as herein described in any of Examples I to V or VII.

10. A liquid which has been clarified by a method according to any of claims 1 to 9.

11. A drink or drink concentrate which contains a liquid according to claim 10 or a concentrate of said - 16 liquid.

12. Meringue prepared from a mixture containing a liquid according to claim 10 or a concentrate of said liquid. 5

13. A drink concentrate according to claim 11, substantially as herein described in Example VI.

14. Meringue according to claim 12, substantially as herein described in Example V.