HK1190040A - Astringency in soy protein solutions - Google Patents

Description

Astringency in soy protein solution

Reference to related applications

This application claims priority from U.S. provisional patent application No. 61/344,946 filed on 24/11/2010, in accordance with 35 USC 119 (e).

Technical Field

The present invention relates to the production of protein solutions from soy with reduced astringency.

Background

In co-pending U.S. patent application No. 12/603,087 filed on 21/10/2009 (U.S. patent publication No. 2010-0098818 (S701) published on 22/4/2010) and U.S. patent application No. 12/923,897 filed on 13/10/2010 (U.S. patent publication No. 2011-0038993 "S701" CIP "published on 17/2/2011), assigned to the assignee hereof, and the disclosures of which are incorporated herein by reference, it is described to provide a soy protein isolate having a protein content of at least about 60 wt% (N x 6.25.25) on a dry weight basis, preferably a protein content of at least about 90 wt% (N x 6.25.25) d.b. The soy protein product has a unique combination of properties, namely:

-is fully soluble in an aqueous medium at an acidic pH of less than about 4.4

-is thermally stable in an aqueous medium at an acidic pH of less than about 4.4

No need for stabilizers or other additives to maintain the protein product in solution

Very low phytic acid

No enzyme is required in its production.

In addition, the soy protein product does not have the beany flavor or off-flavor characteristics of the soy protein product.

This novel soy protein product is prepared by a process comprising:

(a) extracting the soy protein source with an aqueous calcium chloride solution to facilitate solubilization of soy protein from the protein source and form an aqueous soy protein solution,

(b) at least partially separating the aqueous soy protein solution from the residual soy protein source,

(c) optionally diluting the aqueous soy protein solution,

(d) adjusting the pH of the aqueous soy protein solution to a pH of about 1.5 to about 4.4, preferably about 2 to about 4, to produce an acidified clear soy protein solution,

(e) optionally refining (polising) the acidified clear soy protein solution to remove residual particulates,

(f) by using selective membrane technology, the clarified aqueous soy protein solution is optionally concentrated while maintaining the ionic strength substantially constant,

(g) optionally diafiltering the concentrated soy protein solution, and

(h) the concentrated soy protein solution is optionally dried.

Under certain conditions, acidic aqueous solutions of the novel soy protein products exhibit astringency that may impair the use of the soy protein product in particular applications.

Summary of The Invention

One step of the procedures described in the aforementioned U.S. patent application nos. 12/603,087 and 12/923,897 involves adjusting the pH of the optionally diluted soy protein solution to a value of about 1.5 to about 4.4, preferably about 2 to about 4, by the addition of any suitable food grade acid to result in a clear acidified aqueous soy protein solution. The only acids specifically identified in application numbers 12/603,087 and 12/923,897 as being suitable for the acidification step are mineral acids.

It has been found that the astringency perception of acidic aqueous solutions of the novel soy protein products described in application nos. 12/603,087 and 12/923,897 can be significantly reduced by the use of organic acids such as citric acid or malic acid in the acidification step. Preferably, citric acid or a blend of citric acid and malic acid is employed. Furthermore, when citric acid or a citric acid/malic acid blend is used in combination with a mineral acid such as hydrochloric acid or phosphoric acid in any ratio, the astringency sensation is also reduced.

In accordance with one aspect of the present invention, there is provided a method of forming a soy protein product comprising:

(a) extracting the soy protein source with an aqueous calcium salt solution, preferably an aqueous calcium chloride solution, to facilitate solubilization of soy protein from the protein source and form an aqueous soy protein solution,

(b) at least partially separating the aqueous soy protein solution from the residual soy protein source,

(c) optionally diluting the aqueous soy protein solution,

(d) adjusting the pH of the aqueous soy protein solution to a pH of about 1.5 to about 4.4, preferably about 2 to about 4, using at least one organic acid, preferably citric acid or a blend of citric acid and malic acid, alone or in admixture with at least one inorganic acid, optionally in admixture with at least one of hydrochloric acid and phosphoric acid, to produce an acidified clear soy protein solution,

(e) optionally refining the acidified clear soy protein solution to remove residual particulates,

(f) by using selective membrane technology, the clarified aqueous soy protein solution is optionally concentrated while maintaining the ionic strength substantially constant,

(g) optionally diafiltering the concentrated soy protein solution, and

(h) the concentrated and optionally diafiltered soy protein solution is optionally dried.

The soy protein products produced according to the methods herein lack the characteristic beany flavor of soy protein products and are not only suitable for protein fortification of acidic media such as soft drinks and sports drinks, but may also be used in a wide variety of conventional applications of protein products, including but not limited to protein fortification of processed foods and beverages, emulsification of oils, as body formers in baked goods (body formers) and foaming agents in gas-entrapped products. In addition, the soy protein product can form protein fibers useful in meat analogs, and can be used as an egg white substitute or extender in food products where egg white is used as a binder. The soy protein product may also be used in nutritional additives. The soy protein product may also be used in a milk analog product or a product that is a milk/soy blend. Other uses of soy protein products are in pet food, animal feed, and in industrial and cosmetic applications and in personal care products.

Summary of The Invention

The initial step of the process of providing a soy protein product involves solubilizing soy protein from a soy protein source. The soy protein source may be soy or any soy product or by-product derived from soy processing, including but not limited to soy flour, soy flakes, soy meal, and soy flour. The soy protein source may be used in full fat form, partially defatted form, or fully defatted form. When the soy protein source contains appreciable amounts of fat, a degreasing step is typically required during processing. The soy protein recovered from the soy protein source may be a protein naturally occurring in soy, or the proteinaceous material may be a protein modified by genetic manipulation but having hydrophobic and polar properties characteristic of the natural protein.

Protein solubilization from soy protein source material is most conveniently accomplished using calcium chloride solutions, although other calcium salt solutions may be used. In addition, other alkaline earth metal compounds, such as magnesium salts, may be used. Further, extraction of soy protein from a soy protein source may be accomplished using a calcium salt solution in combination with another salt solution, such as sodium chloride. Alternatively, extraction of soy protein from a soy protein source can be accomplished using water or other salt solutions, such as sodium chloride, with the calcium salt subsequently added to the aqueous soy protein solution produced in the extraction step. The precipitate formed after the calcium salt addition was removed prior to subsequent processing.

As the concentration of the calcium salt solution increases, the degree of solubilization of protein from the soy protein source begins to increase until a maximum value is reached. Any subsequent increase in salt concentration did not increase total protein solubilized. The concentration of the calcium salt solution that contributes to maximum protein solubilization varies depending on the salt concerned. It is generally preferred to utilize concentration values less than about 1.0M, and more preferably values from about 0.10 to about 0.15M.

In a batch process, salt dissolution of the protein is achieved at a temperature of about 1 ℃ to about 100 ℃, preferably about 15 ℃ to about 65 ℃, more preferably about 50 ℃ to about 60 ℃, preferably with agitation to reduce the dissolution time, which is typically about 1 to about 60 minutes. Solubilization is preferably effected to extract as much protein from the soy protein source as is substantially achieved so as to provide an overall high yield.

In a continuous process, the extraction of soy protein from a soy protein source is performed in any manner consistent with achieving continuous extraction of soy protein from a soy protein source. In one embodiment, the soy protein source is continuously mixed with the calcium salt solution and the mixture is transported through a pipe or conduit having a length and flow rate sufficient to achieve the desired extraction residence time in accordance with the parameters described herein. In such continuous procedures, the salt solubilization step is effected rapidly in a time up to about 10 minutes, preferably to effect solubilization to extract as much protein from the soy protein source as is substantially achieved. Dissolution in a continuous procedure is achieved at a temperature of from about 1 ℃ to about 100 ℃, preferably from about 15 ℃ to about 65 ℃, more preferably from about 50 ℃ to about 60 ℃.

The extraction is generally carried out at a pH of from about 5 to about 11, preferably from about 5 to about 7. The pH of the extraction system (soy protein source and calcium salt solution) can be adjusted to any desired value in the range of about 5 to about 11 for use in the extraction step by using any convenient food grade acid or food grade base as needed.

The concentration of soy protein source in the calcium salt solution during the solubilization step can vary widely. Typical concentration values are about 5 to about 15% w/v.

The protein extraction step using an aqueous salt solution has the additional effect of dissolving fat that may be present in the soy protein source, which subsequently results in fat being present in the aqueous phase.

The protein solution resulting from the extraction step generally has a protein concentration of about 5 to about 50 g/L, preferably about 10 to about 50 g/L.

The aqueous calcium salt solution may comprise an antioxidant. The antioxidant may be any convenient antioxidant, for example sodium sulfite or ascorbic acid. The amount of antioxidant employed may vary from about 0.01 to about 1 weight percent of the solution, preferably about 0.05 weight percent. The antioxidant serves to inhibit the oxidation of any phenolics in the protein solution.

The aqueous phase resulting from the extraction step may then be separated from the residual soy protein source in any convenient manner, for example by employing a decanter centrifuge or any suitable sieve, followed by disc centrifugation and/or filtration to remove residual soy protein source material. The separated residual soy protein source may be dried for disposal. Alternatively, the separated residual soy protein source may be processed to recover some residual protein. The separated residual soy protein source may be re-extracted with fresh calcium salt solution and the protein solution obtained after clarification combined with the starting protein solution for further processing as described below. Alternatively, the separated residual soy protein source may be processed by conventional isoelectric precipitation procedures or any other convenient procedure to recover residual protein.

As described in U.S. patent nos. 5,844,086 and 6,005,076, assigned to the assignee hereof, and the disclosures of which are incorporated herein by reference, when the soy protein source contains significant amounts of fat, then the defatting step described therein may be accomplished on the isolated aqueous protein solution. Alternatively, the defatting of the separated aqueous protein solution may be achieved by any other convenient procedure.

The aqueous soy protein solution may be treated with an adsorbent, such as powdered activated carbon or granular activated carbon, to remove color and/or odor compounds. Such adsorbent treatment may be carried out under any convenient conditions, typically at the ambient temperature of the separated aqueous protein solution. For powdered activated carbon, amounts of about 0.025% to about 5% w/v, preferably about 0.05% to about 2% w/v, are employed. The adsorbent agent may be removed from the soy solution by any convenient method, such as filtration.

The resulting aqueous soy protein solution may be diluted with generally from about 0.5 to about 10 volumes, preferably from about 0.5 to about 2 volumes, of aqueous diluent to reduce the conductivity of the aqueous soy protein solution to a value generally below about 90 mS, preferably from about 4 to about 18 mS. Such dilution is typically achieved using water, although dilute salt solutions having a conductivity of up to about 3 mS, such as sodium chloride or calcium chloride, may be used.

The diluent with which the soy protein solution is mixed may have a temperature of from about 1 to about 100 c, preferably from about 15 to about 65 c, more preferably from about 50 to about 60 c.

The pH of the optionally diluted soy protein solution is then adjusted to a value of about 1.5 to about 4.4, preferably about 2 to about 4, by the addition of at least one organic acid to result in a clear acidified aqueous soy protein solution. The clear acidified soy protein solution has a conductivity of generally less than about 95 mS for the diluted soy protein solution or less than about 115 mS for the undiluted soy protein solution, in both cases preferably from about 4 to about 23 mS. The organic acid utilized in the acidification step is preferably citric acid or a blend of citric acid and malic acid, which may be used in combination with an inorganic acid such as hydrochloric acid or phosphoric acid in any proportion.

The clarified acidified aqueous soy protein solution may be subjected to a heat treatment to inactivate heat-labile anti-nutritional factors, such as trypsin inhibitors, present in the soy protein source material as a result of extraction from such solution during the extraction step. Such a heating step also provides the additional benefit of reducing the microbial load. Generally, the protein solution is heated to a temperature of about 70 to about 160 ℃ for about 10 seconds to about 60 minutes, preferably to about 80 to about 120 ℃ for about 10 seconds to about 5 minutes, more preferably to about 85 to about 95 ℃ for about 30 seconds to about 5 minutes. The heat treated acidified soy protein solution may then be cooled to a temperature of about 2 to about 65 c, preferably about 50 to about 60 c, for further processing as described below.

The optionally diluted, acidified and optionally heat treated protein solution may optionally be refined by any convenient method, for example by filtration, to remove any residual particulates.

The resulting clear acidified aqueous soy protein solution may be directly dried to produce a soy protein product. To provide a soy protein product, such as a soy protein isolate, having reduced levels of impurities and reduced salt content, the clarified acidified aqueous soy protein solution may be processed prior to drying.

The clarified acidified aqueous soy protein solution may be concentrated to increase its protein concentration while maintaining its ionic strength substantially constant. Such concentration is generally effected to provide a concentrated soy protein solution having a protein concentration of from about 50 to about 300 g/L, preferably from about 100 to about 200 g/L.

The concentration step may be achieved in any convenient manner consistent with batch or continuous operation, for example by employing any convenient selective membrane technique, such as ultrafiltration or diafiltration, using a membrane, such as a hollow fibre membrane or spiral wound membrane, having a suitable molecular weight cut-off, for example from about 3,000 to about 1,000,000 daltons, preferably from about 5,000 to about 100,000 daltons, taking into account the different membrane materials and configurations, and for continuous operation, sized to allow the desired degree of concentration as the aqueous protein solution passes through the membrane.

As is well known, ultrafiltration and similar selective membrane techniques allow low molecular weight species to pass through while preventing higher molecular weight species from passing through. The low molecular weight species include not only the ionic species of the food grade salt, but also low molecular weight materials extracted from the source material, such as carbohydrates, pigments, low molecular weight proteins, and anti-nutritional factors such as trypsin inhibitors (which are themselves low molecular weight proteins). The molecular weight cut-off of the membrane is typically selected to ensure that a significant proportion of the protein remains in solution, while allowing contaminants to pass through, for different membrane materials and configurations.

The concentrated soy protein solution may then be subjected to a diafiltration step using water or a dilute salt solution. The diafiltration solution may be at its natural pH or a pH equal to that of the protein solution to be diafiltered or at any pH value in between. Such diafiltration may be effected using from about 1 to about 40 volumes of diafiltration solution, preferably from about 2 to about 25 volumes of diafiltration solution. In the diafiltration operation, additional quantities of contaminants are removed from the clarified aqueous soy protein solution by passage through a membrane with the permeate (permeate). This purifies the clear aqueous protein solution and may also reduce its viscosity. The diafiltration operation may be effected until no significant further amounts of contaminants or visible colour are present in the permeate, or until the retentate (retenate) has been sufficiently purified so as to provide, upon drying, a soy protein isolate having a protein content of at least about 90 wt% (N x 6.25.25) d.b.. Such diafiltration may be effected using the same membrane as used for the concentration step. However, if desired, the diafiltration step may be effected using separate membranes having different molecular weight cut-offs, for example membranes having molecular weight cut-offs in the range of about 3,000 to about 1,000,000 daltons, preferably about 5,000 to about 100,000 daltons, for different membrane materials and configurations.

Alternatively, a diafiltration step may be applied to the clarified acidified aqueous protein solution or to the partially concentrated clarified acidified aqueous protein solution prior to concentration. Diafiltration may be applied at various points during the concentration process. When diafiltration is applied prior to concentration or to a partially concentrated solution, the resulting diafiltration solution may then be additionally concentrated. The viscosity reduction achieved by diafiltration multiple times as the protein solution is concentrated may allow a higher final fully concentrated protein concentration to be achieved. This reduces the volume of material to be dried.

The concentration step and diafiltration step may be effected herein in such a way that the subsequently recovered soy protein product contains less than about 90 wt% protein (N x 6.25.25) d.b., for example at least about 60 wt% protein (N x 6.25.25) d.b. The contaminants may only be partially removed by partially concentrating and/or partially diafiltering the clarified aqueous soy protein solution. This protein solution may then be dried to provide a soy protein product having a lower level of purity. The soy protein product is still capable of producing a clear protein solution under acidic conditions.

An antioxidant may be present in the diafiltration medium during at least part of the diafiltration step. The antioxidant may be any convenient antioxidant, for example sodium sulfite or ascorbic acid. The amount of antioxidant employed in the diafiltration medium depends on the material employed and may vary from about 0.01 to about 1 wt%, preferably about 0.05 wt%. The antioxidant serves to inhibit oxidation of any phenolics present in the concentrated soy protein solution.

The concentration step and optional diafiltration step may be effected at any convenient temperature, generally from about 2 to about 65 ℃, preferably from about 50 to about 60 ℃, and for a time period to achieve the desired degree of concentration and diafiltration. The temperature and other conditions used depend to some extent on the membrane equipment used to achieve membrane processing, the desired protein concentration of the solution, and the efficiency of contaminant removal from the permeate.

There are two major trypsin inhibitors in soybean, a Kunitz inhibitor which is about 21,000 daltons molecular weight of the thermolabile molecule, and a Bowman-Birk inhibitor which is about 8,000 daltons molecular weight of the more thermostable molecule. The level of trypsin inhibitor activity in the final soy protein product can be controlled by manipulation of various process variables.

As described above, heat treatment of the clarified acidified aqueous soy protein solution may be used to inactivate thermolabile trypsin inhibitors. The partially or fully concentrated acidified soy protein solution may also be heat treated to inactivate thermolabile trypsin inhibitors. When heat treatment is applied to the partially concentrated acidified soy protein solution, the resulting heat treated solution may then be additionally concentrated.

Furthermore, the concentration and/or diafiltration steps may be operated in a manner that is advantageous for removing trypsin inhibitors along with other contaminants in the permeate. Removal of trypsin inhibitors is facilitated by: using a membrane of larger pore size, e.g., from about 30,000 to about 1,000,000 Da, operating the membrane at elevated temperatures, e.g., from about 30 to about 65 c, preferably from about 50 to about 60 c, and employing a larger volume, e.g., from about 10 to about 40 volumes of diafiltration medium.

A protein solution that is acidified and membrane processed diluted at a lower pH of about 1.5 to about 3 can reduce trypsin inhibitor activity relative to a higher pH processed solution at about 3 to about 4.4. When the protein solution is concentrated at the lower end of the pH range and diafiltered, it may be desirable to raise the pH of the retentate prior to drying. The pH of the concentrated and diafiltered protein solution may be raised to a desired value, for example pH 3, by the addition of any convenient food grade base, for example sodium hydroxide.

Further, the reduction in trypsin inhibitor activity may be achieved by exposing the soy material to a reducing agent that disrupts or rearranges the disulfide bonds of the inhibitor. Suitable reducing agents include sodium sulfite, cysteine and N-acetylcysteine.

The addition of such a reducing agent may be achieved at multiple stages of the overall process. The reducing agent may be added along with the soy protein source material in the extraction step, may be added to the clarified aqueous soy protein solution after removal of residual soy protein source material, may be added to the concentrated protein solution before or after diafiltration, or may be dry blended with the dried soy protein product. The addition of the reducing agent may be combined with the heat treatment step and the film processing step, as described above.

If it is desired to retain active trypsin inhibitors in the concentrated protein solution, this can be achieved by: eliminating or reducing the intensity of the heat treatment step, operating the concentration and diafiltration steps at the higher end of the pH range, e.g., pH 3 to about 4.4, without using a reducing agent, operating the membrane at a lower temperature and using a smaller volume of diafiltration medium, using concentration and diafiltration membranes with smaller pore sizes.

As described in U.S. patent nos. 5,844,086 and 6,005,076, a further defatting operation may be performed on the concentrated and optionally diafiltered protein solution, if desired. Alternatively, defatting of the concentrated and optionally diafiltered protein solution may be achieved by any other convenient operation.

The concentrated and optionally diafiltered clear aqueous protein solution may be treated with an adsorbent, such as powdered activated carbon or granular activated carbon, to remove color and/or odorous compounds. Such adsorbent treatment may be performed under any convenient conditions, typically at the ambient temperature of the concentrated protein solution. For powdered activated carbon, amounts of about 0.025% to about 5% w/v, preferably about 0.05% to about 2% w/v, are employed. The adsorbent may be removed from the soy protein solution by any convenient method, such as filtration.

The concentrated and optionally diafiltered clear aqueous soy protein solution may be dried by any convenient technique, such as spray drying or freeze drying. A pasteurization step may be carried out on the soy protein solution prior to drying. Such pasteurization may be effected under any desired pasteurization conditions. Typically, the concentrated and optionally diafiltered soy protein solution is heated to a temperature of about 55 to about 70 ℃, preferably about 60 to about 65 ℃, for about 30 seconds to about 60 minutes, preferably about 10 minutes to about 15 minutes. The pasteurized concentrated soy protein solution may then be cooled for drying, preferably to a temperature of about 25 ℃ to about 40 ℃.

The dry soy protein product has a protein content of greater than about 60 wt% (N x 6.25.25) d.b.. Preferably, the dry soy protein product is an isolate having a high protein content, greater than about 90 wt.% protein, preferably at least about 100 wt.% (N x 6.25.25) d.b..

The soy protein product produced herein is soluble in an aqueous acidic environment, making the product an ideal product for incorporation into carbonated and non-carbonated beverages to provide protein fortification thereto. Such beverages have a wide range of acidic pH values from about 2.5 to about 5. The soy protein product provided herein can be added to such beverages in any convenient amount to provide protein fortification to such beverages, for example at least about 5 g soy protein per serving. The added soy protein product dissolves in the beverage and does not impair the clarity of the beverage even after thermal processing. The soy protein product may be blended with the dry beverage prior to reconstitution of the beverage by dissolution in water. In some instances, modification of the normal formulation of a beverage to tolerate the composition of the invention may be required as components present in the beverage may adversely affect the ability of the composition of the invention to remain dissolved in the beverage.

Examples

Example 1

This example compares the astringency of a soy protein product prepared using acidification with an organic acid with the astringency of a soy protein product prepared using acidification with HCl. Astringency of the protein products was compared by sensory evaluation in commercial beverages.

30 kg of defatted soybean meal (soy white flake) was added to 300L of 0.15M CaCl at ambient temperature₂The solution, and agitated for 30 minutes to provide an aqueous protein solution. The residual soybean meal was removed and the resulting protein solution was clarified by centrifugation to provide an 'a' L protein solution having a 'b'% protein content by weight.

The 'c' L protein solution was then added to the'd' L reverse osmosis purified water and the pH of the sample was lowered to 'e' with the 'f' solution. The diluted and acidified solution was heat treated at 90 ℃ for 30 seconds 'g'.

The heat treated acidified protein solution volume was reduced from 'h' L to 'i' L by concentration on a polyethersulfone membrane having a molecular weight cut-off of 100,000 daltons, operating at a temperature of about 'j' ° c. At this point, the acidified protein solution having a ' k ' wt% protein content was diafiltered with ' L Reverse Osmosis (RO) purified water, wherein the diafiltration operation was performed at about'm ' c. The diafiltered solution was then further concentrated to a volume of 'n' L and diafiltered with an additional 'o' L of RO water, with the diafiltration operation being performed at about 'p' ° c. The protein solution before spray drying was recovered in a yield of 'q' wt% of the initially centrifuged protein solution. The acidified, diafiltered, concentrated protein solution was then dried to obtain the product found to have an 'r'% (N x 6.25.25) d.b. protein content. The product was given the name' S701H. The parameters 'a' to's' for the two runs are set forth in table 1 below.

TABLE 1-parameters from S701H production

s	S016-K02-09A	S016-K03-09A
			a	264	244.3
b	2.72	2.44
			c	264	244.3
d	196	245
			e	2.69	2.89
f	HCl	Citric acid
			g	Followed by filtration
h	460	513
			i	106	101
j	30	30
			k	5.06	4.90
l	138	125
			m	31	30
n	53	50
			o	405	375
p	30	30
			q	65.7	79.2
r	100.96	100.64

Informal taste panels gave unknown samples of S016-K02-09A S701H and S016-K03-09A S701H, prepared by dissolving 2 g protein per 100 ml of cherry flavored commercial beverage known as Kool Aid Jammers. Panelists were asked to identify which samples they felt more astringent and which samples they overall preferred.

Five of the seven panelists felt that the sample containing S016-K02-09A S701H was more astringent than the sample containing S016-K03-09A S701H. Four of the seven panelists preferred the sample containing S016-K03-09A S701H. The comments recorded for the sample containing S016-K03-09A S701H include "more fruit fragrant", "better taste", "less astringent", "less initial sour", "slightly sweeter" and "not astringent".

Example 2

This example compares the astringency of blends using soy protein products prepared by acidification with organic acids with the astringency of blends using soy protein products prepared by acidification with HCl. Astringency of the protein products was compared by sensory evaluation in commercial beverages.

30 kg of defatted soybean meal was added to 300L 'a' M CaCl at ambient temperature₂The solution, and agitated for 30 minutes to provide an aqueous protein solution. The residual soybean meal was removed and the resulting protein solution was clarified by centrifugation to provide a 'b' L protein solution having a 'c'% protein content by weight.

The'd' L protein solution was then added to the 'e' L reverse osmosis purified water and the pH of the sample was lowered to 'f' with the 'g' solution. The diluted and acidified solution was subsequently heat treated at 90 ℃ for 30 seconds.

The heat treated acidified protein solution was reduced in volume from 'h' L to 'i' L by concentration on a polyethersulfone membrane having a molecular weight cut-off of 100,000 daltons, operating at a temperature of about 'j' ° c. At this point, the acidified protein solution having a ' k ' wt% protein content was diafiltered with ' L Reverse Osmosis (RO) purified water, wherein the diafiltration operation was performed at about'm ' c. The diafiltered solution was then further concentrated to a volume of 'n' L and diafiltered with an additional 'o' L of RO water, with the diafiltration operation being performed at about 'p' ° c. After this second diafiltration, the protein solution was concentrated from 'q' protein content to 'r'% protein content by weight, then diluted with water to's'% protein content by weight to facilitate spray drying. The protein solution before spray drying was recovered in a yield of't' wt% of the initially centrifuged protein solution. The acidified, diafiltered, concentrated and diluted protein solution was then dried to obtain the product found to have a 'u'% (N x 6.25.25) d.b. protein content. The product was given the name 'v' S701H. The parameters 'a' to 'v' for the seven runs are set forth in table 2 below.

TABLE 2-parameters from S701H production

Batches of S701H were dry blended in the proportions shown below to provide a composite product referred to as organic acid blend A S701H (table 3) and clariloy XIII S701H (table 4). The organic acid blend A S701H was formulated in such a way that half of the protein content came from batch S019-F21-10A S701H and half came from S019-F22-10A S701H.

Table 3-product proportions in organic acid blend A S701H

Batch wise production of	Weight ratio of the Total product (%)
		S019-F21-10A	50.2
S019-F22-10A	49.8

Table 4-product proportions in Clarisoy XIII S701H

Batch wise production of	Weight ratio of the Total product (%)
		S019-D15-10A	16.9
S019-D19-10A	21.7
		S019-D20-10A	21.2
S019-D21-10A	20.7
		S019-D26-10A	19.5

Informal taste panels gave an blinded sample of organic acid blend A S701H and clariloy XIII S701H, prepared by dissolving 2 g protein per 100 ml of cherry flavored commercial beverage known as Kool Aid Jammers. Panelists were asked to identify which samples they felt more astringent and which samples they overall preferred.

Six of the seven panelists felt that the sample containing the clariloy XIII S701H was more astringent than the sample containing the organic acid blend A S701H. Six of the seven panelists preferred the sample containing the organic acid blend A S701H. The comments recorded for the sample containing the organic acid blend A S701H included "little astringency", "good cherry taste" and "good, clean taste".

Example 3

This example compares the astringency of a soy protein product made using acidification of a blend of organic acids with the astringency of a blend of a soy protein product made using acidification by HCl. Astringency of the protein products was compared by sensory evaluation in commercial beverages.

35 kg of defatted soybean meal was added to 350L of 0.13M CaCl at ambient temperature₂The solution, and agitated for 30 minutes to provide an aqueous protein solution. The residual soybean meal was removed and the resulting protein solution was clarified by sieving and centrifugation to provide 250L of protein solution having a protein content of 2.46% by weight.

250L of protein solution was then added to 193L of reverse osmosis purified water and the pH of the sample was lowered to 3.07 with a solution prepared by dissolving equal weights of malic acid and citric acid in water. The diluted and acidified protein solution was subsequently heat treated at 90 ℃ for 30 seconds.

The heat treated acidified protein solution was reduced in volume from 440L to 102L by concentration on a polyethersulfone membrane having a molecular weight cut-off of 100,000 daltons, operating at a temperature of about 51 ℃. At this point, the acidified protein solution having a protein content of 5.04 wt.% was diafiltered with 163L Reverse Osmosis (RO) purified water, wherein the diafiltration operation was performed at about 50 ℃. The diafiltered solution was then further concentrated to a volume of 44L and diafiltered with an additional 330L of RO water, with the diafiltration operation being performed at about 50 ℃. After this second diafiltration, the protein solution was concentrated from 9.79 protein content to 12.02% protein content by weight, then diluted with water to 5.94% protein content by weight to facilitate spray drying. The protein solution before spray drying was recovered in a yield of 73.8 wt% of the initially centrifuged protein solution. The acidified, diafiltered, concentrated and diluted protein solution was then dried to obtain the product found to have a protein content of 100.56% (N x 6.25.25) d.b.. The product was given the name S020-G13-10A S701H.

Informal taste panels gave unknown samples of S020-G13-10A S701H and Clarisoy XIII S701H prepared by dissolving 2G protein per 100 ml of a commercial cherry flavored beverage known as Kool Aid Jammers. Panelists were asked to identify which samples they felt more astringent and which samples they overall preferred.

Five of the six panelists felt that the sample containing Clarisoy XIII S701H was more astringent than the sample containing S020-G13-10A S701H. Five of the six panelists preferred the sample containing S020-G13-10A S701H. The comments on the sample record containing S020-G13-10A S701H included "sweeter and better cherry taste" and "less astringent taste".

Example 4

This example is a repeat of example 3, but with a different flavor of the commercial beverage. Informal taste panels gave unknown samples of S020-G13-10A S701H and clariloy XIII S701H prepared by dissolving 2G protein per 100 ml of a commercial beverage called Kool Aid Jammers with strawberry kiwi flavour. Panelists were asked to identify which samples they felt more astringent and which samples they overall preferred.

Three of the five panelists felt that the sample containing the Clarisoy XIII S701H was more astringent than the sample containing S020-G13-10A S701H. Three of the five panelists preferred the sample containing S020-G13-10A S701H. The comments on the sample records containing S020-G13-10A S701H included "slightly sweeter".

Example 5

This example compares the same protein samples as examples 3 and 4, but this evaluation was done with purified drinking water instead of flavored beverages. Informal taste panels gave unknown samples of S020-G13-10A S701H and clariloy XIII S701H prepared by dissolving 2G protein per 100 ml of purified drinking water. Panelists were asked to identify which samples they felt more astringent and which samples they overall preferred.

Five of the seven panelists felt that the sample containing the Clarisoy XIII S701H was more astringent than the sample containing S020-G13-10A S701H. Five of the seven panelists preferred the sample containing S020-G13-10A S701H. The comments on the sample records containing S020-G13-10A S701H included "mild" and "much less astringent".

Example 6

This example compares the astringency of a blend using a soy protein product prepared by acidification with an organic acid and a blend using a soy protein product prepared by acidification with HCl with the astringency of a soy protein product prepared by acidification with HCl alone. The astringency of the protein products was compared by sensory evaluation in purified drinking water.

The batches of S701H were dry blended in the proportions shown below to provide a composite product called organic acid/HCl blend A S701H (table 5). The organic acid/HCl blend A S701H was formulated in such a way that half of the protein content came from batches S020-G13-10A S701H and half from Clarisoy XIII S701H.

TABLE 5 product proportions in organic acid/HCl blend A S701H

Batch wise production of	Weight ratio of the Total product (%)
		S020-G13-10A	49.8
Clarisoy XIII	50.2

An informal taste panel gave an blinded sample of organic acid/HCl blend A S701H and clariloy XIII S701H, prepared by dissolving 2 g protein per 100 ml of purified drinking water. Panelists were asked to identify which samples they felt more astringent and which samples they overall preferred.

Five of the seven panelists felt that the sample containing the clariloy XIII S701H was more astringent than the sample containing the organic acid/HCl blend A S701H. Five of the seven panelists preferred the sample containing the organic acid/HCl blend A S701H. The comments recorded for the sample containing the organic acid/HCl blend A S701H included "less astringent", "sweeter and better overall taste", "clean taste" and "little astringent".

Summary of the disclosure

In summary of the present disclosure, a soy protein product, which may be an isolate, produces a clear, heat-resistant solution with reduced astringency 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 using at least one organic acid to produce an acidified clear protein solution, which may be dried after optional concentration and diafiltration to provide a soy protein product. Modifications within the scope of the invention are possible.

Claims (41)

1. A process for preparing a soy protein solution comprising:

(a) extracting a soy protein source with an aqueous calcium salt solution to dissolve soy protein from the soy protein source and form an aqueous soy protein solution,

(b) at least partially separating the aqueous soy protein solution from residual soy protein source, and

(c) the pH of the aqueous soy protein solution is adjusted to a pH of about 1.5 to about 4.4 using at least one organic acid, either alone or in admixture with at least one inorganic acid, to produce an acidified clear soy protein solution.

2. The method of claim 1, wherein the at least one organic acid is citric acid or a blend of citric acid and malic acid.

3. The method of claim 1 wherein the at least one organic acid mixed with at least one inorganic acid is citric acid or a blend of citric acid and malic acid blended with at least one inorganic acid.

4. The method of claim 3, wherein the at least one mineral acid is at least one of hydrochloric acid and phosphoric acid.

5. The method of claim 1, wherein the extracting step is accomplished using an aqueous calcium chloride solution having a concentration of less than about 1.0M, preferably from about 0.10 to about 0.15M.

6. The process of claim 1, wherein the extraction step is effected at a temperature of from about 1 ℃ to about 100 ℃, preferably from about 15 ℃ to about 65 ℃, more preferably from about 50 ℃ to about 60 ℃.

7. The process of claim 1, wherein said extraction with an aqueous calcium salt solution is carried out at a pH of about 5 to about 11, preferably about 5 to about 7.

8. The process of claim 1 wherein the aqueous soy protein solution has a protein concentration of about 5 to about 50 g/L, preferably about 10 to about 50 g/L.

9. The method of claim 1 wherein the aqueous calcium salt solution contains an antioxidant.

10. The process of claim 1 wherein after said separating step and before said pH adjusting step, said aqueous soy protein solution is treated with an adsorbent to remove color and/or odor compounds from the aqueous soy protein solution.

11. The process according to claim 1, wherein after 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, preferably with about 0.5 to about 10 volumes of aqueous diluent to provide a conductivity of about 4 to about 18 mS of said soy protein solution.

12. The process according to claim 11, wherein the aqueous diluent has a temperature of from about 1 ℃ to about 100 ℃, preferably from about 15 ℃ to about 65 ℃, more preferably from about 50 ℃ to about 60 ℃.

13. The method of claim 1 wherein the acidified soy protein solution has a conductivity of less than about 95 mS, preferably about 4 to about 23 mS.

14. The process of claim 1 wherein the pH of the aqueous soy protein solution is adjusted to about pH 2 to about 4.

15. The process of claim 1 wherein the pH adjusted soy protein solution is subjected to a refining step.

16. The method of claim 1, wherein the acidified aqueous protein solution is subjected to a heat treatment step to inactivate thermolabile antinutritional factors, preferably thermolabile trypsin inhibitors, optionally wherein the heat treatment step also reduces the microbial load in the acidified aqueous protein solution.

17. The method of claim 16, wherein the heat treatment is performed at a temperature of about 70 ℃ to about 160 ℃ for about 10 seconds to about 60 minutes, preferably at about 80 ℃ to about 120 ℃ for about 10 seconds to about 5 minutes, more preferably at about 85 ℃ to about 95 ℃ for about 30 seconds to about 5 minutes.

18. The process of claim 16, wherein the heat treated acidified soy protein solution is cooled to a temperature of about 2 ℃ to about 65 ℃, preferably about 50 ℃ to about 60 ℃, for further processing.

19. The process of claim 16 wherein the heat-treated soy protein solution is subjected to a refining step.

20. The process of claim 1 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 x 6.25.25) d.b..

21. The process of claim 1 wherein the acidified clear soy protein solution is concentrated while maintaining its ionic strength substantially constant to produce a concentrated acidified clear soy protein solution having a protein concentration of about 50 to about 300 g/L, preferably about 100 to about 200 g/L, and optionally diafiltered.

22. The method of claim 21, wherein the concentrating step is achieved by ultrafiltration using a membrane having a molecular weight cut-off of about 3,000 to about 1,000,000 daltons, preferably about 5,000 to about 100,000 daltons.

23. The process of claim 21 wherein the diafiltration step is effected using water, acidified water, dilute brine or acidified dilute brine, before or after partial or complete concentration thereof, on the acidified clear soy protein solution.

24. The process of claim 23 wherein said diafiltration is effected using about 1 to about 40 volumes of diafiltration solution, preferably about 2 to about 25 volumes of diafiltration solution.

25. The process of claim 23 wherein the diafiltration is effected until no significant further amounts of contaminants or visible colour are present in the permeate.

26. The process of claim 23 wherein said diafiltration is effected until the retentate has been sufficiently purified so as, when dried, to provide a soy protein isolate having a protein content of at least about 90 wt% (N x 6.25.25) d.b..

27. The process of claim 23 wherein said diafiltration is effected using a membrane having a molecular weight cut-off of about 3,000 to about 1,000,000 daltons, preferably about 5,000 to about 100,000 daltons.

28. The process of claim 23 wherein an antioxidant is present in the diafiltration medium during at least part of the diafiltration step.

29. The process of claim 21 wherein the concentration step and optional diafiltration step are carried out at a temperature of about 2 ℃ to about 65 ℃, preferably about 50 ℃ to about 60 ℃.

30. The process of claim 21 wherein the partially concentrated or concentrated and optionally diafiltered acidified clear soy protein solution is subjected to a heat treatment step to inactivate thermolabile antinutritional factors, including thermolabile trypsin inhibitors.

31. The method of claim 30, wherein the heat treatment is performed at a temperature of about 70 ℃ to about 160 ℃ for about 10 seconds to about 60 minutes, preferably at a temperature of about 80 ℃ to about 120 ℃ for about 10 seconds to about 5 minutes, more preferably at about 85 ℃ to about 95 ℃ for about 30 seconds to about 5 minutes.

32. The process of claim 31, wherein the heat-treated soy protein solution is cooled to a temperature of about 2 ℃ to about 65 ℃, preferably about 50 ℃ to about 60 ℃, for further processing.

33. The process of claim 1 wherein said acidified clear soy protein solution is concentrated and/or diafiltered while maintaining its ionic strength 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 x 6.25.25) d.b..

34. The process of claim 21 wherein said concentrated and optionally diafiltered acidified clear soy protein solution is treated with an adsorbent to remove color and/or odor compounds.

35. The process of claim 21 wherein said concentrated and optionally diafiltered acidified clear soy protein solution is pasteurized prior to drying, wherein said pasteurization step is preferably carried out at a temperature of about 55 ℃ to about 70 ℃ for about 30 seconds to about 60 minutes, more preferably at a temperature of about 60 ℃ to about 65 ℃ for about 10 minutes to about 15 minutes.

36. The process of claim 26 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 x 6.25.25) d.b., preferably at least about 100 wt% (N x 6.25.25) d.b..

37. The process of claim 21 wherein the concentration and/or optional diafiltration step is operated in a manner that facilitates removal of trypsin inhibitors.

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 21 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 33 wherein a reducing agent is added to the concentrated and optionally diafiltered soy protein solution and/or a reducing agent is added to the dried soy protein product to disrupt or rearrange the disulfide bonds of trypsin inhibitors to achieve a reduction in trypsin inhibitor activity prior to drying the soy protein product.

41. A soy protein product having reduced astringency.