Production of soluble protein solutions from soy ("s701" cip)

Abstract

A soy protein product, which may be an isolate, produces transparent heat-stable solutions at low pH values and is useful for the fortification of soft drinks and sports drinks without precipitation of protein. The soy protein product is obtained by extracting a soy protein source material with an aqueous calcium salt solution to form an aqueous soy protein solution, separating the aqueous soy protein solution from residual soy protein source, adjusting the pH of the aqueous soy protein solution to a pH of about 1.5 to about 4.4 to produce an acidified clear soy protein solution, which may be dried, following optional concentration and diafiltration, to provide the soy protein product.

What we claim is: 
     
         1 . A soy protein product which has a protein content of at least about 60 wt % (N×6.25) d.b. and which
 is completely soluble in aqueous media at acid pH values of less than about 4.4 
 is heat-stable in aqueous media at acid pH values of less than about 4.4 
 does not require stabilizers or other additives to maintain the protein product in solution or suspension 
 is low in phytic acid 
 requires no enzymes in the production thereof. 
 
     
     
         2 . The soy protein product of  claim 1  which has no beany flavour or off odors. 
     
     
         3 . The soy protein product of  claim 1  wherein the soy protein has not been hydrolyzed. 
     
     
         4 . The soy protein product of  claim 1  which is low in trypsin inhibitor activity. 
     
     
         5 . The soy protein product of  claim 1  which has a protein content of at least about 90 wt % (N×6.25) d.b. 
     
     
         6 . The soy protein product of  claim 1  which has a protein content of at least about 100 wt % (N×6.25) d.b. 
     
     
         7 . The soy protein product of  claim 1  which has a phytic acid content of less than about 1.5 wt %, preferably less than about 0.5 wt %. 
     
     
         8 . A soy protein product having a protein content of at least about 60 wt % (N×6.25) d.b. which is substantially completely soluble in an aqueous medium at a pH of less than about 4.4. 
     
     
         9 . The soy protein product of  claim 8  which is a soy protein isolate having a protein content of at least about 90 wt % (N×6.25) d.b. 
     
     
         10 . The soy protein product of  claim 8  which is blended with water-soluble powdered materials for the production of aqueous solutions of the blend. 
     
     
         11 . The blend of  claim 10  which is a powdered beverage. 
     
     
         12 . An aqueous solution of the soy protein product of  claim 8  which is heat stable at a pH value of less than about 4.4. 
     
     
         13 . The aqueous solution of  claim 12  which is a beverage. 
     
     
         14 . The aqueous solution of  claim 13  wherein the beverage is a clear beverage in which the soy protein product is completely soluble and transparent. 
     
     
         15 . The aqueous solution of  claim 13  wherein the beverage is an opaque beverage in which the dissolved soy protein product does not increase the opacity. 
     
     
         16 . The aqueous solution of  claim 12  wherein the soy protein product is a soy protein isolate having a protein content of at least about 90 wt % (N×6.25) d.b. 
     
     
         17 . A soy protein product having a protein content of at least about 60 wt % (N×6.25) d.b. which is substantially completely soluble in an aqueous medium at a pH of about 7 to about 8. 
     
     
         18 . An aqueous solution with a near neutral pH, preferably in the range of about 6 to about 8, having dissolved therein the soy product of  claim 17 . 
     
     
         19 . The aqueous solution of  claim 18  which is a beverage. 
     
     
         20 . The aqueous solution of  claim 18  which is incorporated in the manufacture of a dairy analogue or a product that is a dairy/soy blend. 
     
     
         21 . The aqueous solution of  claim 18  which is heat stable. 
     
     
         22 . The aqueous solution of  claim 18  which is transparent at a pH of about 7.5 to about 8. 
     
     
         23 . A soy protein product which has a protein content of at least about 60 wt % (N×6.25) d.b. which has a solubility at 1% protein w/v in water at a pH of about 2 to about 4 of greater than about 95%, as determined by the methods described in Example 14. 
     
     
         24 . A soy protein product having a protein content of at least about 60 wt % (N×6.25) d.b. which has an absorbance of visible light at 600 nm (A600) for a 1% protein w/v aqueous solution at a pH of about 2 to about 4 of less than about 0.150, as determined by the method described in Example 15. 
     
     
         25 . The soy protein product of  claim 24  wherein the A600 reading is less than about 0.100. 
     
     
         26 . The soy protein product of  claim 24  wherein the A600 reading is less than about 0.050. 
     
     
         27 . A soy protein product having a protein content of at least about 60 wt % (N×6.25) d.b. which has a haze reading for a 1% protein w/v aqueous solution at a pH of about 2 to about 4, of less than about 15%, as determined by the method described in Example 15. 
     
     
         28 . The soy protein product of  claim 27  wherein the haze reading is less than about 10% 
     
     
         29 . The soy protein product of  claim 27  wherein the haze reading is less than about 5%. 
     
     
         30 . A soy protein product having a protein content of at least about 60 wt % (N×6.25) d.b. which has a haze reading for a solution in water, prepared by dissolving 2 g of protein per 100 ml of water used, after heat treatment at 95° C. for 30 seconds of less than 15%, as determined by the method described in Example 16. 
     
     
         31 . The soy protein product of  claim 30  wherein the haze reading is less than about 10%. 
     
     
         32 . The soy protein product of  claim 30  wherein the haze reading is less than about 5%. 
     
     
         33 . The soy protein product of any one of  claims 17  or  23  to  32  which has a protein content of at least about 90 wt % (N×6.25) d.b. 
     
     
         34 . A soy protein product having a protein content of at least about 60 wt % (N×6.25) d.b. which has colorimeter readings for a solution thereof in water, prepared by dissolving sufficient soy protein product to supply 3.2 g of protein per 100 ml of water used, which are a combination of L*=about 82 to about 100, a*=about −2 to about 5 and b*=about 0 to about 30. 
     
     
         35 . The soy protein product of  claim 34  wherein said colorimeter readings are a combination of L*=about 94 to about 100, a*=about −1 to about 1 and b*=about 0 to about 10. 
     
     
         36 . The soy protein product of  claim 34  which has a protein content of at least about 90 wt % (N×6.25) d.b., preferably at least about 100 wt % (N×6.25) d.b. 
     
     
         37 . A process for the preparation of a soy protein solution, which comprises:
 (a) extracting a soy protein source with an aqueous calcium salt solution to cause solubilization of soy protein from the soy protein source and to form an aqueous soy protein solution,   (b) at least partially separating the aqueous soy protein solution from residual soy protein source, and   (c) adjusting the pH of the aqueous soy protein solution to a pH of about 1.5 to about 4.4 to produce an acidified soy protein solution.   
     
     
         38 . The process of  claim 37  wherein said extraction step is effected using an aqueous calcium chloride solution having a concentration of less than about 1.0 M. 
     
     
         39 . The process of  claim 38  wherein said aqueous calcium chloride solution has a concentration of about 0.10 to about 0.15 M. 
     
     
         40 . The process of  claim 37  wherein said extraction step is effected at a temperature of about 15° to about 60° C., preferably about 15° to about 35° C. 
     
     
         41 . The process of  claim 37  wherein said extraction with aqueous calcium salt solution is conducted at a pH of about 5 to about 11. 
     
     
         42 . The process of  claim 41  wherein said pH is about 5 to about 7. 
     
     
         43 . The process of  claim 37  wherein said aqueous soy protein solution has a protein concentration of about 5 to about 50 g/L. 
     
     
         44 . The process of  claim 43  wherein said protein concentration is about 10 to about 50 g/L. 
     
     
         45 . The process of  claim 37  wherein said aqueous calcium salt solution contains an antioxidant. 
     
     
         46 . The process of  claim 37  wherein, following said separation step and prior to said pH adjustment step, said aqueous soy protein solution is treated with an adsorbent to remove colour and/or odour compounds from the aqueous soy protein solution. 
     
     
         47 . The process of  claim 37  wherein, following said separation step and prior to said pH adjustment step, said aqueous soy protein solution is diluted to a conductivity of less than about 90 mS. 
     
     
         48 . The process of  claim 47  wherein said aqueous soy protein solution is diluted with about 0.5 to about 10 volumes of aqueous diluent to provide a conductivity of said soy protein solution of about 4 to about 18 mS. 
     
     
         49 . The process of  claim 47  wherein said aqueous diluent has a temperature of about 2° to about 70° C. 
     
     
         50 . The process of  claim 49  wherein said temperature is about 10° to about 50° C. 
     
     
         51 . The process of  claim 50  wherein said temperature is about 20° to about 30° C. 
     
     
         52 . The process of  claim 37  wherein said acidified soy protein solution has a conductivity of less than about 95 mS. 
     
     
         53 . The process of  claim 52  wherein said conductivity is about 4 to about 23 mS. 
     
     
         54 . The process of  claim 37  wherein the pH of said aqueous soy protein solution is adjusted to about pH 2 to about 4. 
     
     
         55 . The process of  claim 37  wherein the pH-adjusted soy protein solution is subjected to a polishing step. 
     
     
         56 . The process of  claim 37 , wherein said acidified aqueous protein solution is subjected to a heat treatment step to inactivate heat-labile anti-nutritional factors. 
     
     
         57 . The process of  claim 56  wherein the anti-nutritional factors are heat-labile trypsin inhibitors. 
     
     
         58 . The process of  claim 56  wherein the heat treatment step also pasteurizes the acidified aqueous protein solution. 
     
     
         59 . The process of  claim 56 , wherein said heat treatment is effected at a temperature of about 70° to about 160° C. for about 10 seconds to about 60 minutes. 
     
     
         60 . The process of  claim 59  wherein said heat treatment is effected at a temperature of about 80° to about 120° C. for about 10 seconds to about 5 minutes. 
     
     
         61 . The process of  claim 60  wherein said heat treatment is effected at a temperature of about 85° C. to about 95° C. for about 30 seconds to about 5 minutes. 
     
     
         62 . The process of  claim 56  wherein the heat treated acidified soy protein solution is cooled to a temperature of about 2° to about 60° C. for further processing. 
     
     
         63 . The process of  claim 62  wherein the heat treated acidified soy protein solution is cooled to a temperature of about 20° to about 35° C. for further processing. 
     
     
         64 . The process of  claim 56  wherein the heat treated soy protein solution is subjected to a polishing step. 
     
     
         65 . The process of  claim 37  wherein said acidified clear soy protein solution is dried to provide a soy protein product having a soy protein content of at least about 60 wt % (N×6.25) d.b. 
     
     
         66 . The process of  claim 37  wherein said acidified clear soy protein solution is concentrated while maintaining the ionic strength thereof substantially constant to produce a concentrated acidified clear soy protein solution having a protein concentration of about 50 to about 300 g/L and the concentrated acidified clear soy protein solution is optionally diafiltered. 
     
     
         67 . The process of  claim 66  wherein said concentrated acidified clear soy protein solution has a protein concentration of about 100 to about 200 g/L. 
     
     
         68 . The process of  claim 66  wherein said concentration step is effected by ultrafiltration using a membrane having a molecular weight cut-off of about 3,000 to about 1,000,000 Daltons. 
     
     
         69 . The process of  claim 68  wherein said membrane has a molecular weight cut-off of about 5,000 to about 100,000 Daltons. 
     
     
         70 . The process of  claim 66  wherein a diafiltration step is effected using water, acidified water, dilute saline or acidified dilute saline on the acidified clear soy protein solution before or after partial or complete concentration thereof. 
     
     
         71 . The process of  claim 70  wherein said diafiltration is effected using about 2 to about 40 volumes of diafiltration solution. 
     
     
         72 . The process of  claim 71  wherein said diafiltration is effected using about 5 to about 25 volumes of diafiltration solution. 
     
     
         73 . The process of  claim 70  wherein said diafiltration is effected until no significant further quantities of contaminants or visible colour are present in the permeate. 
     
     
         74 . The process of  claim 70  wherein said 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 % (N×6.25) d.b. 
     
     
         75 . The process of  claim 70  wherein said diafiltration is effected using a membrane having a molecular weight cut-off of about 3,000 to about 1,000,000 Daltons. 
     
     
         76 . The process of  claim 75  wherein said membrane has a molecular weight cut-off of about 5,000 to about 100,000 Daltons. 
     
     
         77 . The process of  claim 70  wherein an antioxidant is present in the diafiltration medium during at least part of the diafiltration step. 
     
     
         78 . The process of  claim 66  wherein said concentration step and optional diafiltration step are carried out at a temperature of about 2° to about 60° C. 
     
     
         79 . The process of  claim 78  wherein said temperature is about 20° to about 35° C. 
     
     
         80 . The process of  claim 66  wherein the partially concentrated or concentrated and optionally diafiltered acidified clear soy protein solution is subjected to a heat treatment step to inactivate heat-labile anti-nutritional factors, including heat-labile trypsin inhibitors. 
     
     
         81 . The process of  claim 80  wherein said heat treatment is effected at a temperature of about 70° to about 160° C. for about 10 seconds to about 60 minutes, preferably a temperature of about 80° C. to about 120° C. for about 10 seconds to about 5 minutes, more preferably about 85° C. to about 95° C. for about 30 seconds to about 5 minutes. 
     
     
         82 . The process of  claim 81  wherein the heat treated soy protein solution is cooled to a temperature of about 2° to about 60° C., preferably about 20° to about 35° C., for further processing. 
     
     
         83 . The process of  claim 37  wherein said acidified clear soy protein solution is concentrated and/or diafiltered while maintaining the ionic strength thereof substantially constant to produce a concentrated and/or diafiltered acidified clear soy protein solution which, when dried, provides a soy protein product having a protein concentration of at least about 60 wt % (N×6.25) d.b. 
     
     
         84 . The process of  claim 66  wherein said concentrated and optionally diafiltered acidified clear soy protein solution is treated with an adsorbent to remove colour and/or odour compounds. 
     
     
         85 . The process of  claim 66  wherein said concentrated and optionally diafiltered acidified clear soy protein solution is pasteurized prior to drying. 
     
     
         86 . The process of  claim 85  wherein said pasteurization step is effected at a temperature of about 55° to about 70° C. for about 30 seconds to about 60 minutes. 
     
     
         87 . The process of  claim 86  wherein said pasteurization step is effected at a temperature of about 60° to about 65° C. for about 10 to about 15 minutes. 
     
     
         88 . The process of  claim 74  wherein said concentrated and diafiltered acidified clear soy protein solution is dried to provide a soy protein isolate having a protein content of at least about 90 wt % (N×6.25) d.b. 
     
     
         89 . The process of  claim 88  wherein said soy protein isolate has a protein content of at least about 100 wt % (N×6.25) d.b. 
     
     
         90 . The process of  claim 66  wherein the concentration and/or optional diafiltration step are operated in a manner favourable to the removal of trypsin inhibitors. 
     
     
         91 . The process of  claim 37  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. 
     
     
         92 . The process of  claim 66  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. 
     
     
         93 . The process of  claim 83  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.