PREPARATION OF SOY PROTEIN PRODUCT USING WATER EXTRACTION ("S803")

Abstract

A soy protein product which is completely soluble and is capable of providing transparent and heat stable solutions at low and neutral pH values is produced by extracting a soy protein source material with water at low pH, subjecting the resulting aqueous soy protein solution to ultrafiltration and optional diafiltration to provide a concentrated and optionally diafiltered soy protein solution, which may be dried to provide the soy protein product. The soy protein product may be used for protein fortification of, in particular, soft drinks and sports drinks, without precipitation of protein.

Claims

1. A process of preparing a soy protein product having a soy protein content of at least about 60 wt % (N6.25) on a dry weight basis, which comprises: (a) extracting a soy protein source with water at low pH to cause solubilization of soy protein from the protein source and to form an aqueous soy protein solution, (b) separating the aqueous soy protein solution from residual soy protein source, (c) concentrating the aqueous soy protein solution using a selective membrane technique, (d) optionally diafiltering the concentrated soy protein solution, and (e) optionally drying the concentrated soy protein solution.

2. The process of claim 1 wherein said water has a pH of about 1.5 to about 3.6.

3. The process of claim 2 wherein the pH is about 2.6 to about 3.6.

4. The process of claim 1 wherein said extraction step is effected at a temperature of about 15 C. to about 35 C.

5. The process of claim 1 wherein said aqueous soy protein solution has a protein concentration of about 5 to about 50 g/L.

6. The process of claim 5 wherein said aqueous soy protein solution has a protein concentration of about 10 to about 50 g/L.

7. The process of claim 1 wherein said water contains an antioxidant.

8. The process of claim 1 wherein said aqueous soy protein solution is treated with an adsorbent to remove colour and/or odour compounds from the aqueous soy protein solution.

9. The process of claim 1 wherein said aqueous soy protein solution is subjected to a heat treatment to inactivate heat labile anti-nutritional factors.

10. The process of claim 9 wherein the anti-nutritional factors are heat-labile trypsin inhibitors.

11. The process of claim 9 wherein the heat treatment step also pasteurizes the acidified clear aqueous protein solution.

12. The process of claim 9 wherein said heat treatment step is effected at a temperature of about 70 to about 120 C. for about 10 seconds to about 60 minutes.

13. The process of claim 12 wherein said heat treatment step is effected at a temperature of about 85 to about 95 C. for about 30 seconds to about 5 minutes.

14. The process of claim 9 wherein the heat-treated soy protein solution is cooled to a temperature of about 2 to about 60 C. for further processing.

15. The process of claim 14 wherein the heat-treated soy protein solution is cooled to a temperature of about 20 to about 35 C. for further processing.

16. The process of claim 1 wherein the aqueous soy protein solution is concentrated to a protein concentration of about 50 to about 400 g/L.

17. The process of claim 16 wherein the aqueous protein solution is concentrated to a protein concentration of about 100 to about 250 g/L.

18. The process of claim 1 wherein the aqueous soy protein solution is concentrated using a membrane having a molecular weight cut-off of about 3,000 to about 1,000,000 Daltons.

19. The process of claim 18 wherein the aqueous soy protein solution is concentrated using a membrane having a molecular weight cut-off of about 5,000 to about 100,000 Daltons.

20. The process of claim 1 wherein the optional diafiltration step is effected using water or acidified water on the soy protein solution before or after complete concentration thereof.

21. The process of claim 20 wherein the optional diafiltration step is effected using from about 2 to about 40 volumes of diafiltration solution.

22. The process of claim 21 wherein the optional diafiltration step is effected using from about 5 to about 25 volumes of diafiltration solution.

23. The process of claim 20 wherein said diafiltration step is effected using a membrane having a molecular weight cut-off of about 3,000 to about 1,000,000 Daltons.

24. The process of claim 23 wherein said diafiltration step is effected using a membrane having a molecular weight cut-off of about 5,000 to about 100,000 Daltons.

25. The process of claim 20 wherein an antioxidant is present during at least part of the diafiltration step.

26. The process of claim 20 wherein said optional diafiltration step is effected until no significant further quantities of contaminants or visible colour are present in the permeate.

27. The process of claim 20 wherein said optional diafiltration is effected until the retentate has been sufficiently purified so as, when dried, to provide a soy protein product with a protein content of at least about 60 wt % (N6.25) d.b.

28. The process of claim 27 wherein said optional diafiltration is effected until the retentate has been sufficiently purified so as, when dried, to provide a soy protein isolate with a protein content of at least about 90 wt % (N6.25) d.b.

29. The process of claim 28 wherein said optional diafiltration is effected until the retentate has been sufficiently purified so as, when dried, to provide a soy protein isolate with a protein content of at least about 100 wt % (N6.25) d.b.

30. The method of claim 1 wherein said concentration step and optional diafiltration step are carried out at a temperature of about 2 to about 60 C.

31. The method of claim 30 wherein said temperature is about 20 to about 35 C.

32. The process of claim 1 wherein the concentration and/or optional diafiltration step are operated in a manner favourable to the removal of trypsin inhibitors.

33. The process of claim 1 wherein the concentrated and optionally diafiltered soy protein solution is treated with an adsorbent to remove colour and/or odour compounds prior to said drying step.

34. The process of claim 1 wherein the concentrated and optionally diafiltered soy protein solution is pasteurized prior to drying.

35. The method of claim 34 wherein said pasteurization step is effected at a temperature of about 55 to about 70 C. for about 30 seconds to about 60 minutes.

36. The method of claim 35 wherein said pasteurization step is effected at a temperature of about 60 to about 65 C. for about 10 to about 15 minutes.

37. The method of claim 34 wherein said pasteurized, concentrated and optionally diafiltered soy protein solution is cooled to a temperature of about 15 C. to about 35 C. for drying or further processing.

38. The process of claim 1 wherein a reducing agent is present during the extraction step to disrupt or rearrange the disulfide bonds of trypsin inhibitors to achieve a reduction in trypsin inhibitor activity.

39. The process of claim 1 wherein a reducing agent is present during the concentration and/or optional diafiltration step to disrupt or rearrange the disulfide bonds of trypsin inhibitors to achieve a reduction in trypsin inhibitor activity.

40. The process of claim 1 wherein a reducing agent is added to the concentrated and optionally diafiltered soy protein solution prior to drying and/or the dried soy protein product to disrupt or rearrange the disulfide bonds of trypsin inhibitors to achieve a reduction in trypsin inhibitor activity.

41. The process of claim 1 wherein the concentrated and optionally diafiltered soy protein solution is dried to provide a soy protein product having a protein content of about 60 to about 90 wt % (N6.25) d.b.

42. The process of claim 1 wherein the concentrated and optionally diafiltered soy protein solution is dried to provide a soy protein isolate having a protein content of at least about 90 wt % (N6.25) d.b.

43. The process of claim 1 wherein the concentrated and optionally diafiltered soy protein solution is dried to provide a soy protein isolate having a protein content of at least about 100 wt % (N6.25) d.b.

44. A soy protein product produced by the process of claim 1.

45. An acidic solution having dissolved therein the soy protein product of claim 44.

46. The aqueous solution of claim 45 which is a beverage.

47. The soy protein product of claim 44 which is blended with water-soluble powdered materials for the production of aqueous solutions of the blend.

48. The blend of claim 47 which is a powdered beverage.

49. A neutral solution having dissolved therein the soy protein product of claim 44.

Description

EXAMPLES

Example 1

[0051] This Example is an evaluation of the extractability of defatted, minimally heat processed soy flour with water or saline at low pH.

[0052] Defatted, minimally heat processed soy flour (10 g) was extracted with either water, 0.15 NaCl or 0.15M CaCl.sub.2 (100 ml) with the pH of the extraction system adjusted to 3 with diluted HCl. Flour and solvent were combined, the pH adjusted and then the samples stirred for 30 minutes at room temperature using a magnetic stir bar and stir plate. The extract was separated from the spent meal by centrifugation at 10,200 g for 10 minutes and then further clarified by filtration with a 0.45 m pore size syringe filter. The protein content of the filtrates was measured using a LECO FP528 Nitrogen Determinator and then the samples were diluted with an equal volume of water and observed for the presence of precipitate.

[0053] The extractability results are set forth in the following Table 1:

TABLE-US-00001 TABLE 1 Effect of extraction solvent on protein content of pH 3 extracts sample % protein extractability (%) water 3.38 62.2 sodium chloride 2.94 54.1 calcium chloride 3.79 69.8

[0054] As may be seen from the results of Table 1, the extractability was quite high for all the solvents, with the calcium chloride solution solubilizing the most protein. Extraction with water alone solubilized more protein than using 0.15M sodium chloride solution.

[0055] When the clarified extracts were diluted with water, the sodium chloride extract precipitated heavily, while the water and calcium chloride extracts stayed essentially clear.

Example 2

[0056] This Example is an examination of the extractability of soy flour with water at various pH values and the clarity of the resulting extracts when acidified to pH 3.

[0057] Defatted, minimally heat processed soy flour (10 g) was extracted with reverse osmosis purified water (100 ml) for 30 minutes at room temperature using a magnetic stir bar/stir plate operated at constant speed. Timing of the 30 minutes for extraction started when stirring commenced. The pH of the extraction (water plus flour) was adjusted to 3, 5, 7, 9 or 11 with 6M HCl or 6M NaOH immediately after the flour was entirely wetted (which occurred quite quickly) and monitored and corrected throughout the 30 minute extraction. After 30 minutes, the samples were centrifuged at 10,200 g for 10 minutes to separate extract from the spent meal. The extracts were then further clarified by filtration with a 0.45 m pore size syringe filter. The protein content of the filtered extracts was assessed using a LECO FP528 Nitrogen Determinator. The pH and clarity (A600) of the filtered extracts were also measured. A sample of filtered extract was diluted with one part reverse osmosis purified water and the pH and clarity of the diluted sample assessed. The full strength and diluted samples were then adjusted to pH 3 with 6M HCl or 6M NaOH as necessary and the clarity re-evaluated.

[0058] The effect of extraction pH on the extractability of the soy flour with water is set forth in the following Table 2:

TABLE-US-00002 TABLE 2 Effect of pH on the extractability of soy flour with water extraction pH % protein in extract extractability (%) 3 2.43 45.4 5 0.70 13.1 7 4.05 75.7 9 4.28 80.0 11 5.18 96.8

[0059] As can be seen by the results in Table 2, significant extractabilities were obtained using water at alkaline pH. Although lower, the extractability obtained at pH 3 was a reasonable value.

[0060] The effect of acidification on the clarity of the full strength extract samples is set forth in the following Table 3:

TABLE-US-00003 TABLE 3 Effect of acidification on the clarity of full strength water extracts extraction pH initial pH initial A600 adjusted pH final A600 3 2.88 0.089 2.96 0.095 5 4.99 0.007 3.05 2.58 7 6.96 0.155 3.04 >3.0 9 8.87 0.222 3.02 >3.0 11 10.92 0.173 2.95 >3.0

[0061] As can be seen in the results of Table 3, the sample extracted at pH 3 was the only sample that remained clear after pH adjustment.

[0062] The effect of acidification on the clarity of the diluted extract samples is set forth in the following Table 4:

TABLE-US-00004 TABLE 4 Effect of acidification on the clarity of diluted water extracts extraction pH initial pH initial A600 adjusted pH final A600 3 2.97 0.222 5 5.06 0.001 2.96 2.53 7 6.97 0.080 3.02 >3.0 9 8.80 0.129 2.97 0.334 11 10.86 0.062 2.96 1.55

[0063] As can be seen from the results of Table 4, the sample extracted at pH 3 and then diluted was the clearest of those evaluated.

Example 3

[0064] This Example was conducted to determine if a low pH water extract of soy flour would stay clear when concentrated and diafiltered and also re-hydrate clear after drying.

[0065] 80 g of defatted, minimally heat processed soy flour was added to 800 ml of reverse osmosis purified water at ambient temperature and agitated for 30 minutes to provide an aqueous protein solution. Immediately after the flour was dispersed in the water, the pH of the system was adjusted to 3 by the addition of diluted HCl. The pH was monitored and corrected to 3 periodically over the course of the 30 minute extraction. The residual soy flour was removed and the resulting protein solution was clarified by centrifugation and filtration to produce 475 ml of filtered protein solution having a protein content of 1.86% by weight.

[0066] The filtered protein solution was reduced in volume to 42 ml by concentration on a polyethersulfone (PES) membrane having a molecular weight cut-off of 10,000 Daltons. An aliquot of 40 ml of concentrated protein solution was diafiltered with 80 ml of reverse osmosis purified water. The resulting diafiltered, concentrated protein solution had a protein content of 15.42% by weight and represented a yield of 69.2 wt % of the initial filtered protein solution. The diafiltered, concentrated protein solution was then dried to yield a product found to have a protein content of 90.89% (N6.25) w.b. The product was termed S803.

[0067] A 3.2 wt % protein solution of S803 in water was prepared and the colour and clarity assessed using a HunterLab Color Quest XE instrument operated in transmission mode.

[0068] The colour and clarity values are set forth in the following Table 5:

TABLE-US-00005 TABLE 5 HunterLab scores for 3.2% protein solution of S803 sample L* a* b* haze (%) S803 96.97 1.39 10.87 17.6

[0069] As may be seen from Table 5, the colour of the S803 solution was very light and the haze level was quite low.

Example 4

[0070] In this Example, the heat stability of the S803 product, produced according to the procedure of Example 3, was assessed.

[0071] A 2% w/v protein solution of S803 in water was produced. The pH of the solution was determined with a pH meter and the clarity of the solution was assessed by haze measurement with the HunterLab Color Quest XE instrument. The solution was then heated to 95 C., held at this temperature for 30 seconds and then immediately cooled to room temperature in an ice bath. The clarity of the heat treated solution was then measured.

[0072] The pH of the S803 solution was 2.91. The clarity of the protein solution before and after heating is set forth in the following Table 6:

TABLE-US-00006 TABLE 6 Effect of heat treatment on clarity of S803 solution sample haze (%) before heating 53.8 after heating 32.4

[0073] As can be seen from Table 6, the clarity of the 2% solution of S803 was inferior to that of the 3.2% solution prepared in Example 3. The reason for this was unknown. In any case, when the 2% protein solution was heat treated the haze level in the sample was reduced. Therefore, heat treatment did not impair the clarity.

Example 5

[0074] In this Example, the production of S803 was scaled up from benchtop to pilot plant scale.

[0075] a kg of defatted, minimally heat processed soy flour was added to b L of reverse osmosis purified water at ambient temperature and agitated for 30 minutes to provide an aqueous protein solution. Immediately after the flour was dispersed in the water, the pH of the system was adjusted to 3 by the addition of dilute HCl. The pH was monitored and corrected to 3 periodically over the course of the 30 minute extraction. The residual soy flour was removed and the resulting protein solution was clarified by centrifugation and filtration to produce c L of filtered protein solution having a protein content of d% by weight.

[0076] The filtered protein solution was reduced in volume to e L by concentration on a f membrane having a molecular weight cut-off of g Daltons. An aliquot of h L of concentrated protein solution with a protein content of i% by weight and representing a yield of T wt % of the initial filtered protein solution was dried to yield a product found to have a protein content of k% (N6.25) d.b. The product was termed 1 S803-02. The remaining m L of concentrated protein solution was diafiltered with n L of reverse osmosis purified water o. The resulting diafiltered, concentrated protein solution had a protein content of p% by weight and represented a yield of q wt % of the initial filtered protein solution. The diafiltered, concentrated protein solution was then dried to yield a product found to have a protein content of r)/0 (N6.25) d.b. The product was termed 1 S803.

[0077] The parameters a to r for two runs are set forth in the following Table 7:

TABLE-US-00007 TABLE 7 Parameters for the runs to produce S803 l S005-L16-08A S005-A20-09A a 20 20 b 200 200 c 170 210 d 0.71 0.91 e 18.46 25 f PVDF PVDF g 5,000 5,000 h 2 0 i 6.21 n/a j 9.9 n/a k 95.96 n/a m 16.46 25 n 34 50 o adjusted to pH 3 at natural pH with diluted HCl p 6.29 8.69 q 86.0 93.2 r 94.63 98.36 n/a = not applicable

[0078] 3.2% w/v protein solutions of S005-L16-08A S803, S803-02 and S005-A20-09A S803 were prepared in water and the colour and clarity assessed using a HunterLab Color Quest XE instrument operated in transmission mode. The pH was also measured with a pH meter.

[0079] The pH, colour and clarity values are set forth in the following Table 8:

TABLE-US-00008 TABLE 8 pH and HunterLab scores for 3.2% protein solutions of S005-L16-08A S803, S803-02 and S005-A20-09A S803 sample pH L* a* b* haze (%) S005-L16-08A S803 3.37 96.09 0.24 9.17 2.9 S005-L16-08A S803-02 3.52 96.11 0.90 10.29 8.9 S005-A20-09A S803 3.13 95.98 0.65 9.98 10.2

[0080] As may be seen from Table 8, the colours of the S803 solutions were very light and the haze levels were low.

[0081] The colour of the dry powders was also assessed with the HunterLab Color Quest XE instrument in reflectance mode. The colour values are set forth in the following Table 9:

TABLE-US-00009 TABLE 9 HunterLab scores for S005-L16-08A S803, S803-02 and S005-A20-09A S803 dry powders sample L* a* b* S005-L16-08A S803 87.88 0.02 6.90 S005-L16-08A S803-02 88.84 0.28 7.83 S005-A20-09A S803 87.07 0.03 8.47

[0082] As may be seen from Table 9, all dry products were very light in colour.

Example 6

[0083] This Example contains an evaluation of the heat stability in water of the soy protein isolates produced by the method of Example 5 (S803).

[0084] 2% w/v protein solutions of S005-L16-08A S803 and S005-A20-09A S803 were produced in water and the pH adjusted to 3. The clarity of these solutions was assessed by haze measurement with the HunterLab Color Quest XE instrument in transmission mode. The solutions were then heated to 95 C., held at this temperature for 30 seconds and then immediately cooled to room temperature in an ice bath. The clarity of the heat treated solutions was then measured again.

[0085] The clarity of the protein solutions before and after heating is set forth in the following Table 10:

TABLE-US-00010 TABLE 10 Effect of heat treatment on clarity of S005- L16-08A S803 and S005-A20-09A S803 solutions Haze (%) Haze (%) sample before heating after heating S005-L16-08A S803 5.0 1.7 S005-A20-09A S803 16.2 13.5

[0086] As can be seen from the results in Table 10, the clarity of these 2% solutions of S803 prepared at pilot scale as described in Example 5 was much better than the clarity of the 2% solution of S803 prepared at laboratory scale as described in Example 3. It is unknown why this difference occurred. As was the case in Example 4, the solutions of 5803 were found to be heat stable with the heat treatment appearing to improve the clarity.

Example 7

[0087] This Example contains an evaluation of the solubility in water of the soy protein isolates produced by the method of Example 5 (S803). Solubility was tested based on protein solubility (termed protein method, a modified version of the procedure of Mon et al., J. Food Sci. 50:1715-1718) and total product solubility (termed pellet method).

[0088] Sufficient protein powder to supply 0.5 g of protein was weighed into a beaker and then a small amount of reverse osmosis (RO) purified water was added and the mixture stirred until a smooth paste formed. Additional water was then added to bring the volume to approximately 45 ml. The contents of the beaker were then slowly stirred for 60 minutes using a magnetic stirrer. The pH was determined immediately after dispersing the protein and was adjusted to the appropriate level (2, 3, 4, 5, 6 or 7) with diluted NaOH or HCl. A sample was also prepared at natural pH. For the pH adjusted samples, the pH was measured and corrected two times during the 60 minutes stirring. After the 60 minutes of stirring, the samples were made up to 50 ml total volume with RO water, yielding a 1% w/v protein dispersion. The protein content of the dispersions was measured using a LECO FP528 Nitrogen Determinator. Aliquots (20 ml) of the dispersions were then transferred to pre-weighed centrifuge tubes that had been dried overnight in a 100 C. oven then cooled in a desiccator and the tubes capped. The samples were centrifuged at 7800 g for 10 minutes, which sedimented insoluble material and yielded a clear supernatant. The protein content of the supernatant was measured by LECO analysis and then the supernatant and the tube lids were discarded and the pellet material dried overnight in an oven set at 100 C. The next morning the tubes were transferred to a desiccator and allowed to cool. The weight of dry pellet material was recorded. The dry weight of the initial protein powder was calculated by multiplying the weight of powder used by a factor of ((100moisture content of the powder (%))/100). Solubility of the product was then calculated two different ways:

Solubility (protein method) (%)=(% protein in supernatant/% protein in initial dispersion)1001)

Solubility (pellet method) (%)=(1(weight dry insoluble pellet material/((weight of 20 ml of dispersion/weight of 50 ml of dispersion)initial weight dry protein powder)))1002)

[0089] The natural pH values of the protein isolates produced in Example 5 in water (1% protein) are shown in Table 11:

TABLE-US-00011 TABLE 11 Natural pH of solutions prepared in water at 1% protein Batch Product Natural pH S005-L16-08A S803 3.36 S005-A20-09A S803 3.14

[0090] The solubility results obtained are set forth in the following Tables 12 and 13:

TABLE-US-00012 TABLE 12 Solubility of S803 at different pH values based on protein method Solubility (protein method) (%) Prod- Nat. Batch uct pH 2 pH 3 pH 4 pH 5 pH 6 pH 7 pH S005-L16-08A S803 92.6 95.7 66.3 16.1 84.4 100 92.9 S005-A20-09A S803 90.3 95.7 29.3 10.1 90.1 86.9 91.8

TABLE-US-00013 TABLE 13 Solubility of S803 at different pH values based on pellet method Solubility (pellet method) (%) Prod- Nat. Batch uct pH 2 pH 3 pH 4 pH 5 pH 6 pH 7 pH S005-L16-08A S803 97.2 97.1 67.5 22.5 84.1 97.8 97.1 S005-A20-09A S803 97.1 96.9 36.3 26.5 88.1 97.5 97.2

[0091] As can be seen from the results of Tables 12 and 13, the S803 products were extremely soluble at pH values of 2, 3 and 7 and at the natural pH.

Example 8

[0092] This Example contains an evaluation of the clarity in water of the soy protein isolates produced by the method of Example 5 (S803).

[0093] The clarity of the 1% w/v protein dispersions prepared as described in Example 7 was assessed by measuring the absorbance at 600 nm, with a lower absorbance score indicating greater clarity. Analysis of the samples on a HunterLab Color Quest XE instrument in transmission mode also provided a percentage haze reading, another measure of clarity.

[0094] The clarity results are set forth in the following Tables 14 and 15:

TABLE-US-00014 TABLE 14 Clarity of S803 solutions at different pH values as assessed by A600 A600 Prod- Nat. Batch uct pH 2 pH 3 pH 4 pH 5 pH 6 pH 7 pH S005-L16-08A S803 0.013 0.026 >3.0 >3.0 1.077 0.021 0.036 S005-A20-09A S803 0.031 0.070 >3.0 >3.0 0.704 0.034 0.065

TABLE-US-00015 TABLE 15 Clarity of S803 solutions at different pH values as assessed by HunterLab analysis HunterLab haze reading (%) Prod- Nat. Batch uct pH 2 pH 3 pH 4 pH 5 pH 6 pH 7 pH S005-L16-08A S803 1.8 4.6 95.7 96.1 83.2 1.7 4.9 S005-A20-09A S803 1.4 9.5 95.4 95.7 68.2 0.0 8.6

[0095] As can be seen from the results of Tables 14 and 15, solutions of 5803 exhibited excellent clarity at pH values of 2, 3 and 7 and at the natural pH.

Example 9

[0096] This Example contains an evaluation of the solubility in a soft drink (Sprite) and sports drink (Orange Gatorade) of the soy protein isolate produced by the method of Example 5 (S803). The solubility was determined with the protein added to the beverages with no pH correction and again with the pH of the protein fortified beverages adjusted to the level of the original beverages.

[0097] When the solubility was assessed with no pH correction, a sufficient amount of protein powder to supply 1 g of protein was weighed into a beaker and a small amount of beverage was added and stirred until a smooth paste formed. Additional beverage was added to bring the volume to 50 ml, and then the solutions were stirred slowly on a magnetic stirrer for 60 minutes to yield a 2% protein w/v dispersion. The protein content of the samples was analyzed using a LECO FP528 Nitrogen Determinator then an aliquot of the protein containing beverages was centrifuged at 7800 g for 10 minutes and the protein content of the supernatant measured.

Solubility (%)=(% protein in supernatant/% protein in initial dispersion)100

[0098] When the solubility was assessed with pH correction, the pH of the soft drink (Sprite) (3.39) and sports drink (Orange Gatorade) (3.19) without protein was measured. A sufficient amount of protein powder to supply 1 g of protein was weighed into a beaker and a small amount of beverage was added and stirred until a smooth paste formed. Additional beverage was added to bring the volume to approximately 45 ml, and then the solutions were stirred slowly on a magnetic stirrer for 60 minutes. The pH of the protein containing beverages was measured and then adjusted to the original no-protein pH with HCl or NaOH as necessary. The total volume of each solution was then brought to 50 ml with additional beverage, yielding a 2% protein w/v dispersion. The protein content of the samples was analyzed using a LECO FP528 Nitrogen Determinator then an aliquot of the protein containing beverages was centrifuged at 7800 g for 10 minutes and the protein content of the supernatant measured.

Solubility (%)=(% protein in supernatant/% protein in initial dispersion)100

[0099] The results obtained are set forth in the following Table 16:

TABLE-US-00016 TABLE 16 Solubility of S803 in Sprite and Orange Gatorade no pH correction pH correction Solubility Solubility Solubility (%) in Solubility (%) in (%) in Orange (%) in Orange Batch Product Sprite Gatorade Sprite Gatorade S005-L16-08A S803 97.7 100 100 100 S005-A20-09A S803 100 100 100 100

[0100] As can be seen from the results of Table 16, the 5803 was extremely soluble in the Sprite and the Orange Gatorade. As 5803 is an acidified product, protein addition had little effect on beverage pH.

Example 10

[0101] This Example contains an evaluation of the clarity in a soft drink and sports drink of the soy protein isolate produced by the method of Example 5 (S803).

[0102] The clarity of the 2% w/v protein dispersions prepared in soft drink (Sprite) and sports drink (Orange Gatorade) in Example 9 were assessed using the methods described in Example 8. For the absorbance measurements at 600 nm, the spectrophotometer was blanked with the appropriate beverage before the measurement was performed.

[0103] The results obtained are set forth in the following Tables 17 and 18:

TABLE-US-00017 TABLE 17 Clarity (A600) of S803 in Sprite and Orange Gatorade no pH correction pH correction A600 A600 A600 in Orange A600 in Orange Batch Product in Sprite Gatorade in Sprite Gatorade S005-L16-08A S803 0.062 0.220 0.067 0.484 S005-A20-09A S803 0.132 0.101 0.099 0.115

TABLE-US-00018 TABLE 18 HunterLab haze readings for S803 in Sprite and Orange Gatorade no pH correction pH correction haze haze haze (%) in haze (%) in (%) in Orange (%) in Orange Batch Product Sprite Gatorade Sprite Gatorade no protein 0.0 44.0 0.0 44.0 S005-L16-08A S803 10.7 65.7 17.0 81.9 S005-A20-09A S803 24.8 59.2 14.4 52.3

[0104] As can be seen from the results of Tables 17 and 18, the S005-L16-08A S803 increased the haze in Orange Gatorade much more than the S005-A20-09A 5803 did. The reason for this was unknown. When both 5803 products were put into Sprite, the beverage was substantially clear or perhaps slightly hazy.

SUMMARY OF THE DISCLOSURE

[0105] In summary of this disclosure, the present invention provides a method of producing a soy protein product which is soluble in acid media, based on water extraction of a soy protein source material. Modifications are possible within the scope of this invention.