HK1176241B - Ph adjusted soy protein isolate and uses - Google Patents

Description

pH adjusted soy protein isolate and uses

Technical Field

The present invention relates to a pH adjusted soy protein isolate and uses thereof.

Background

In us patent application No. 12/603,087 (us publication No. 2010-0098818, WO 2010/045727) (S701) filed on 21/10/2009 (assigned to the assignee of the present invention and the disclosure of which is incorporated herein by reference), a method of preparing a novel soy protein isolate is described which produces a clear and heat stable solution at low pH and thus can be used for protein fortification, particularly of soft and sports drinks and other aqueous systems, without producing protein precipitates.

The soy protein isolate produced herein has a combination of parameters not found in other soy isolates. The article is fully soluble at an acidic pH of less than about 4.4 and its solution is thermally stable at this pH range, allowing for thermal processing, such as hot-fill applications. No stabilizers or other additives are required to maintain the protein in solution or suspension. The soy protein isolate has no beany flavor and no off-flavor. The product has low phytic acid content, and does not require enzyme in the preparation of soy protein isolate. Soy protein isolate is highly soluble at about pH 7.

The soy protein content of this novel soy protein isolate is at least about 90 wt.%, preferably at least about 100 wt.% (N x 6.25) (dry weight basis (d.b.)), prepared by a process comprising:

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

(b) 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 about 1.5 to about 4.4, preferably about 2 to about 4, to produce an acidified clear soy protein solution,

(e) optionally heat treating the acidified solution to reduce the activity and microbial load of the anti-nutritional trypsin inhibitor,

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

(g) optionally diafiltering the concentrated soy protein solution,

(h) optionally pasteurizing the concentrated soy protein solution to reduce microbial load, and

(i) optionally drying the concentrated soy protein solution.

Summary of The Invention

One of the important attributes of the soy protein products produced in the above-mentioned U.S. patent application is the clean, beany flavor of the product, in contrast to the unique beany flavor of conventional soy protein isolates.

The soy protein products prepared in the above-mentioned U.S. patent application produce low pH solutions when dissolved in water. While a low pH of the soy protein product is desirable in acidic food applications (e.g., preparing acidic beverages), it may not be desirable for other food applications (e.g., foods having a near neutral pH). It may be preferred to use a protein preparation that is already near neutral, rather than formulating and adding other ingredients with the acidic protein component to raise the pH to the desired level. Commercial soy protein isolates are typically provided at or near neutral pH.

The present invention provides soy protein isolates that lack the beany flavor characteristic of conventional soy protein isolates; provided at a near neutral pH; and as with conventional soy protein isolates, can be used in food applications at near neutral pH conditions. Some of the articles provided herein are poorly soluble in water at a pH ranging from about 4 to about 7, while others are substantially insoluble in water at a pH ranging from about 2 to about 7.

While a range of soy protein isolate products are suitable for food use with a variety of functional properties and a variety of intended applications, some of the more common applications for commercial soy protein isolates are in nutritional bars (nutrition bars) and meat processing products. The pH adjusted soy protein isolate of the present invention is free of the beany flavor of conventional isolates and can replace conventional isolates in a variety of food products, including those of the above-mentioned variety, to provide flavor-improved food products. The process for preparing the pH adjusted soy protein isolate described below may include a heat treatment step that serves to modify the functional properties of the isolate, i.e., reduce the solubility of the protein and increase the hydration capacity of the material.

Accordingly, another aspect of the present invention provides a process for preparing a soy protein product comprising:

providing an aqueous soy protein product solution having a protein content of at least about 60 wt% (N x 6.25) (d.b.), which is fully soluble in an aqueous medium below about pH4.4 and is heat stable at this pH range,

adjusting the pH of the solution to about pH6 to precipitate the soy protein thus obtained, and

optionally drying the whole pH-adjusted sample, or

Optionally recovering and drying the precipitated material, or

Optionally heat treating the pH-adjusted solution and then drying the entire sample, or

Optionally heat treating the pH adjusted solution and then recovering and drying the precipitated material.

In another aspect of the present invention, the concentrated soy protein product prepared according to the methods of the above-mentioned U.S. patent applications can be processed to produce the pH-adjusted soy protein product provided herein. Thus, in a further aspect of the invention, there is provided a process for preparing a soy protein product as provided herein, which comprises:

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

(b) 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 heat treating the acidified solution to reduce the activity and microbial load of the anti-nutritional trypsin inhibitor,

(f) concentrating the clarified aqueous soy protein solution using a selective membrane technique while maintaining the ionic strength substantially constant,

(g) optionally diafiltering the concentrated soy protein solution,

(h) optionally pasteurizing the concentrated soy protein solution to reduce the microbial load,

(i) adjusting the pH of the aqueous soy protein solution to about pH6 to precipitate the soy protein thus obtained, and

optionally drying the whole pH-adjusted sample, or

Optionally recovering and drying the precipitated material, or

Optionally heat treating the pH-adjusted solution and then drying the entire sample, or

Optionally heat treating the pH adjusted solution and then recovering and drying the precipitated material.

The heat treatment of the pH-adjusted solution is typically accomplished under the following conditions: from about 70 ℃ to about 160 ℃ for from about 2 seconds to about 60 minutes, preferably from about 80 ℃ to about 120 ℃ for from about 15 seconds to about 15 minutes, more preferably from about 85 ℃ to about 95 ℃ for from about 1 minute to about 5 minutes.

The process options described herein enable the preparation of soy protein isolates having a range of functional properties, increasing the utility of pH adjusted soy protein isolates as food ingredients and as substitutes for conventional soy protein isolate ingredients.

While the present invention is primarily directed to the preparation and use of soy protein isolate having a protein content of at least about 90 wt% (N x 6.25) (dry weight (d.b.) basis), preferably at least about 100 wt%, it is contemplated that less pure soy protein products having similar properties to soy protein isolate may be provided and used. Such less pure preparations may have a protein concentration of at least about 60 wt% (N × 6.25) (d.b.). These soy protein products can be used in place of conventional soy protein products in a variety of food applications.

Detailed Description

The first step in preparing the pH adjusted soy protein product of this invention is to prepare the soy protein product as follows according to the above-mentioned U.S. patent application No. 12/603,087.

The steps of the process for providing the soy protein product initially include dissolving soy protein from a soy protein source. The soy protein source may be soy or any soy product or byproduct derived from soy processing, including but not limited to soy flour (soy meal), soy meal (soy flake), soy grits (soy grit), and soy flour. The soy protein source may be used in a full fat form, a partially defatted form, or a fully defatted form. When the soy protein source contains significant amounts of fat, a de-oiling 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 protein material may be a protein modified by gene manipulation but possessing the hydrophobic and polar properties characteristic of natural proteins.

The protein is most conveniently dissolved from the soy protein source material using a calcium chloride solution, although other calcium salt solutions may be used. In addition, other alkaline earth metal compounds, such as magnesium salts, may be used. In addition, soy protein can be extracted from a soy protein source using a calcium salt solution in combination with another salt solution, such as sodium chloride. Alternatively, soy protein may be extracted from the soy protein source using water or other salt solutions, such as sodium chloride, followed by the addition of calcium salts to the aqueous soy protein solution produced in the extraction step. The precipitate formed during the addition of the calcium salt is removed first and the subsequent treatment is carried out.

As the concentration of the calcium salt solution increases, the degree of protein dissolution from the soy protein source begins to increase until a maximum value is reached. Any subsequent increase in salt concentration no longer increases the total protein solubilized. The concentration of calcium salt solution that allows the maximum amount of protein to be solubilized varies with the salt concerned. It is generally preferred to use concentration values of less than about 1.0M, more preferably values of from about 0.10M to about 0.15M.

In a batch process, salt dissolution of the protein is carried out at a temperature of from about 1 ℃ to about 100 ℃, preferably from about 15 ℃ to about 60 ℃, more preferably from about 15 ℃ to about 35 ℃, preferably with agitation to reduce the dissolution time, which is typically from about 1 to about 60 minutes. It is preferred to perform the solubilization to extract protein from the soy protein source in as large an amount as possible in order to provide a high overall yield.

In the continuous process, the extraction of soy protein from the soy protein source is performed in any manner consistent with the continuous extraction of soy protein from the soy protein source. In one embodiment, the soy protein source is continuously mixed with the calcium salt solution and the mixture is conveyed through a pipe or conduit having a length and at a flow rate for a residence time sufficient to effect the desired extraction according to the parameters described herein. In such continuous processing, the salt solubilization step is carried out rapidly over a period of up to about 10 minutes, preferably as much as possible to extract protein from the soy protein source in large quantities. Dissolution is carried out in a continuous process at a temperature of from about 1 ℃ to about 100 ℃, preferably from about 15 ℃ to about 60 ℃, more preferably from about 15 ℃ to about 35 ℃.

The extraction step 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 extract 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 the extraction step using any convenient food grade acid (typically hydrochloric or phosphoric acid) or food grade base (typically sodium hydroxide) as needed.

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

The step of extracting the protein with aqueous salt solution has the additional effect of dissolving fat that may be present in the soy protein source, which then results in fat being present in the aqueous phase.

The protein solution obtained 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 contain an antioxidant. The antioxidant may be any convenient antioxidant, such as 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 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 screen, 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 produced in the clarification step, along with the starting protein solution, may be further processed 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.

When the soy protein source contains a significant amount of fat (as described in U.S. Pat. Nos. 5,844,086 and 6,005,076, which are assigned to the assignee of the present invention and the disclosures of which are incorporated herein by reference), the isolated aqueous protein solution may then be subjected to the defatting step described therein. Alternatively, defatting of the separated aqueous protein solution may be accomplished 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 room 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 may be removed from the soy solution by any convenient means, for example by filtration.

The resulting aqueous soy protein solution may be diluted with 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. This dilution is typically done using water, but dilute salt solutions having a conductivity of up to about 3 mS, such as sodium chloride or calcium chloride, may also be used.

The diluent mixed with the soy protein solution may have a temperature of from about 2 ℃ to about 70 ℃, preferably from about 10 ℃ to about 50 ℃, more preferably from about 20 ℃ to about 30 ℃.

The pH of the diluted soy protein solution is then adjusted to about 1.5 to about 4.4, preferably about 2 to about 4, by the addition of any suitable food grade acid to produce a clear acidified aqueous soy protein solution. The clear acidified aqueous soy protein solution has a conductivity of generally less than about 95 mS, preferably about 4 to about 23 mS.

The acidified clear aqueous soy protein solution may be heat treated to inactivate heat-labile anti-nutritional factors (e.g., trypsin inhibitors) that are present in such solution as a result of extraction from the soy protein source material during the extraction step. The 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 about 80 ℃ to about 120 ℃ for about 10 seconds to about 5 minutes, more preferably 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 60 ℃, preferably about 20 ℃ to about 35 ℃ for further processing as described below.

The optionally diluted, acidified and optionally heat treated protein solution may optionally be purified (poise) by any convenient method, such as filtration, to remove any residual particulates.

The resulting acidified clear soy protein solution may be directly dried to produce a soy protein product. To provide soy protein products, such as soy protein isolates, having reduced levels of impurities and reduced salt concentrations, the clear soy protein solution may be acidified prior to drying.

The acidified clear soy protein solution may be concentrated to increase its protein concentration while maintaining its ionic strength substantially constant. The concentration is generally carried out 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 carried out 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 a spiral wound membrane, with a suitable molecular weight cut-off, taking into account the different membrane materials and structures, of, for example, about 3,000 to about 1,000,000 daltons, preferably about 5,000 to about 100,000 daltons, and for continuous operation, the dimensions may be adjusted to allow the desired degree of concentration as the aqueous protein solution passes through the membrane.

It is well known that ultrafiltration and similar selective membrane techniques allow low molecular weight species to pass therethrough while preventing higher molecular weight species from passing therethrough. The low molecular weight substances include not only ionic substances of food grade salts but also low molecular weight materials extracted from source materials, 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, taking into account the different membrane materials and structures.

The concentrated soy protein solution may then be subjected to a diafiltration step using water or dilute saline solution. The diafiltration solution may be at its natural pH, or at a pH equal to that of the protein solution being diafiltered, or at any pH value in between. The diafiltration may be effected using from about 2 to about 40 volumes of diafiltration solution, preferably from about 5 to about 25 volumes of diafiltration solution. In the diafiltration operation, the amount of contaminants is further removed from the clarified aqueous soy protein solution by passage through the membrane with the permeate. This step purifies the clear aqueous protein solution and also reduces its viscosity. The diafiltration operation may be effected until no significantly greater amounts of contaminants or visible colour are present in the permeate or 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) d.b.. The diafiltration may be effected using the same membrane as 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 a molecular weight cut-off in the range of about 3,000 to about 1,000,000 daltons, preferably about 5,000 to about 100,000 daltons, taking into account the different membrane materials and configurations.

Alternatively, the diafiltration step may be used to clarify the acidified aqueous protein solution prior to concentration, or to partially concentrate the clarified acidified aqueous protein solution. Diafiltration may also be performed at various points during the concentration process. When diafiltration is performed prior to concentration or on a partially concentrated solution, the resulting diafiltered solution may then be further concentrated. The reduction in viscosity achieved by multiple diafiltrations as the protein solution is concentrated may allow a higher final concentration of fully concentrated protein to be obtained. This reduces the volume of material to be dried.

The concentration step and diafiltration step may be performed herein in such a way that the subsequently recovered soy protein product contains less than about 90 wt% protein (N x 6.25) d.b., for example at least about 60 wt% protein (N x 6.25) 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 can 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 a portion of the diafiltration step. The antioxidant may be any convenient antioxidant, such as sodium sulfite or ascorbic acid. The amount of antioxidant employed in the diafiltration medium depends on the material used 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 carried out at any convenient temperature (generally about 2 ℃ to about 60 ℃, preferably about 20 ℃ to about 35 ℃) for a period of time to achieve the desired degree of concentration and diafiltration. The temperature and other conditions used will depend to some extent on the membrane equipment used to perform the membrane treatment, the desired protein concentration of the solution and the efficiency of the removal of contaminants to the permeate.

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

As noted above, heat treatment of acidified clear aqueous soy protein solutions can 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 the partially concentrated acidified soy protein solution is subjected to heat treatment, the resulting heat treated solution may then be further concentrated.

In addition, the concentration and/or diafiltration steps may be operated in a manner that facilitates removal of trypsin inhibitors along with other contaminants in the permeate. Removal of trypsin inhibitors can be facilitated by: the use of larger pore size (e.g., about 30,000 to about 1,000,000Da) membranes, operating the membranes at elevated temperatures (e.g., about 30 ℃ to about 60 ℃), and utilizing a larger volume (e.g., about 20 to about 40 volumes) of diafiltration medium.

Acidification and membrane treatment of the diluted protein solution at lower pH (about 1.5 to about 3) reduces trypsin inhibitor activity compared to processing the solution at higher pH (about 3 to about 4.4). When concentrating and diafiltering the protein solution at the low end of the pH range, it may be desirable to increase 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.

In addition, a reduction in trypsin inhibitor activity can be achieved by exposing the soy material to a reducing agent that cleaves or rearranges the disulfide bonds of the inhibitor. Suitable reducing agents include sodium sulfite, cysteine and N-acetyl cysteine.

The reducing agent may be added at different stages of the overall process. The reducing agent may be added with the soy protein source material during the extraction step, may be added to the clear aqueous soy protein solution after removal of residual soy protein source material, may be added to the concentrated protein solution before or after diafiltration, and may be dry blended with the dried soy protein product. The addition of the reducing agent may be combined with the above-described heat treatment step and film treatment step.

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; no reducing agent is used; operating the concentration and diafiltration steps at the high end of the pH range (e.g., about 3 to about 4.4); using concentration and diafiltration membranes with smaller pore sizes; operating the membrane at a lower temperature and using a smaller volume of diafiltration medium.

If desired, the concentrated and optionally diafiltered protein solution may be subjected to further defatting operations as described in U.S. Pat. Nos. 5,844,086 and 6,005,076. Alternatively, defatting the concentrated and optionally diafiltered protein solution may be achieved by any other suitable procedure.

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 odor compounds. Such adsorbent treatment may be carried out under any convenient conditions, typically at room 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 means, for example by 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. The soy protein solution may be subjected to a pasteurization step prior to drying. This pasteurization may be carried out under any desired pasteurization conditions. The concentrated and optionally diafiltered soy protein solution is typically heated to a temperature of about 55 c to about 70 c, preferably about 60 c to about 65 c, 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 freeze dried, preferably to a temperature of about 25 ℃ to about 40 ℃.

The protein content of the dried soy protein product is greater than about 60 wt% (N x 6.25) d.b.. Preferably the dried soy protein product is an isolate having a high protein content, said content exceeding about 90 wt.% protein, preferably at least about 100 wt.% (N x 6.25) d.b..

Various methods can be used to provide the pH adjusted soy protein isolate of the present invention from acid soluble soy protein isolate and to manipulate its functional properties.

In one such method, the acidic soy protein isolate preparation obtained as described above is formed into an aqueous solution, the pH of the aqueous solution is raised to about pH6, and the material is dried. Alternatively, the precipitate formed upon adjusting the pH to 6 is recovered and these solids are dried to produce a soy protein isolate. Still alternatively, the solution of pH6 may be heated to a temperature of about 70 ℃ to about 160 ℃ for about 2 seconds to about 60 minutes, preferably about 80 ℃ to about 120 ℃ for about 15 seconds to about 15 minutes, more preferably about 85 ℃ to about 95 ℃ for about 1 to about 5 minutes, followed by drying the entire sample, or in yet another method, recovering and drying only the insoluble solids from the heat-treated sample.

In another option, the concentrated protein solution from step (h) above used to prepare the acid soluble soy protein product may be adjusted to a pH of about 6 to cause precipitation of the protein. The entire sample may then be dried, or the precipitated solid may be collected and merely dried to form an isolate. Alternatively, the solution of pH6 may be heated to a temperature of about 70 ℃ to about 160 ℃ for about 2 seconds to about 60 minutes, preferably about 80 ℃ to about 120 ℃ for about 15 seconds to about 15 minutes, more preferably about 85 ℃ to about 95 ℃ for about 1 to about 5 minutes, followed by drying all of the sample or just the precipitated material.

In the step of collecting and drying the precipitated solids, the remaining soluble protein fraction may also be processed to form a soy protein product. The soluble fraction may be directly dried or further processed by membrane concentration and/or diafiltration and/or heat treatment before drying.

Examples

In the following examples, all lyophilized products were ground to a powder, the protein content of the powder was determined by the combustion method using a Leco nitrogen terminator, and the moisture of the powder was determined by the oven drying method. The spray dried product was analyzed similarly, but without milling prior to analysis.

Sensory evaluation of the samples was performed as follows:

samples were evaluated organoleptically as 2% protein w/v dispersions in purified drinking water at about pH 6. An informal panel of 6-8 panelists was invited to make blind evaluations to compare the experimental samples with the S013-K19-09A conventional IEP pH6 product samples (prepared as described in example 1 below), and to indicate which sample had a more pronounced beany flavor.

Example 1

This example illustrates the preparation of soy protein isolate by conventional isoelectric precipitation.

At room temperature, 30 kg of white soybean meal (soy white flake) was added to 300L of RO water, and the pH was adjusted to 8.5 by adding 1M sodium hydroxide solution. The sample was stirred for 30 minutes to provide an aqueous protein solution. The pH of the extraction process was monitored and maintained at 8.5 throughout 30 minutes. The residual white soybean meal was removed and the resulting protein solution was clarified by centrifugation and filtration to yield 278.7L of filtered protein solution having a protein content of 2.93 wt%. A precipitate formed by adding diluted HCl which had been used to equal volumes to adjust the pH of the protein solution to 4.5. The pellet was collected by centrifugation and then washed by resuspending it in 2 volumes of RO water. The washed precipitate was then collected by centrifugation. A total of 32.42 kg of washed precipitate was obtained, the protein content of which was 18.15% by weight. This represents a protein yield of 72.0% in the clear extraction solution. An aliquot of 16.64 kg of the washed precipitate was combined with an equal weight of RO water and the pH of the sample was adjusted to 6 using sodium hydroxide. The pH adjusted sample was then spray dried to produce an isolate with a protein content of 93.80% (N x 6.25.25) d.b. The product was named S013-K19-09A conventional I ° Ρ pH 6.

Example 2

This example illustrates one method of preparing a pH adjusted soy protein isolate.

30 kg of minimally heat-treated defatted soy flour was added to 300L of 0.15M CaCl at room temperature₂To the solution, and stirred for 30 minutes to provide an aqueous protein solution. 300L of 0.075M CaCl were additionally added₂The solution was dissolved and the residual soy flour was removed and the resulting protein solution was clarified by centrifugation to yield 532.5L of centrifuged protein solution having a protein content of 1.22 wt%. The pH of the sample was then lowered to 3.09 using dilute HCl.

The diluted and acidified protein extract solution volume was reduced from 532L to 107L by centrifugation on a Polyethersulfone (PES) membrane having a molecular weight cut-off of 100,000 daltons. The concentration step and the subsequent membrane treatment step are both carried out at about 30 ℃. The solution was diafiltered using 370L of Reverse Osmosis (RO) purified water, then further concentrated to provide 37.86 kg of a concentrated protein solution having a protein content of 13.97 wt%. This represents a yield of 81.4 wt% of the initial clarified protein solution.

A1.5 kg sample of concentrated protein solution was treated with 25% w/v aqueous sodium hydroxide solution to raise the pH of the sample to 6 and a precipitate formed. The precipitate was collected by centrifugation at 10,000 g and then lyophilized to form a product designated S009-D27-09AS701N, which had a protein content of 106.53 wt% (N x 6.25.25) on a dry weight basis.

Sensory evaluation all panelists (6/6) at S009-D27-09A S70 IN rated the sample as less beany than the conventional IEP control (prepared as described IN example 1).

Example 3

This example illustrates another method for preparing a pH adjusted soy protein isolate.

60 kg of minimally heat treated defatted soy flour was added to 600L of 0.15M CaCl at room temperature₂To the solution, and stirred for 30 minutes to provide an aqueous protein solution. 600L of 0.075M CaCl were additionally added₂The solution was removed and the residual soy flour was removed and the resulting protein solution was clarified by centrifugation and filtration to yield 975L of filtered protein solution having a protein content of 1.15 wt%. Half the volume of water was added and the pH of the sample was lowered to 3.05 using dilute HCl.

The diluted and acidified protein extract solution volume was reduced from 1505L to 305L by centrifugation on a Polyethersulfone (PES) membrane having a molecular weight cut-off of 100,000 daltons. The concentration step and the subsequent membrane treatment step are both carried out at about 30 ℃. The solution was diafiltered using 650L of Reverse Osmosis (RO) purified water and then further concentrated to provide 59.44 kg of a concentrated protein solution having a protein content of 15.51 wt%. This represents a yield of 82.2 wt% of the initial filtered protein solution.

In a subsequent heating step, a 10.20 kg sample of concentrated protein solution was diluted with an equal volume of water to aid mixing.

The pH of the diluted solution was adjusted to 6 using 25% w/v aqueous sodium hydroxide solution and then heated to 95 ℃ for 5 minutes while mixing in a jacketed steam kettle. Adjusting to pH6 produced a large amount of precipitation.

The heated solution was then cooled and the precipitated material was separated from the soluble fraction by centrifugation at 4,000 g. The obtained precipitate was resuspended in Reverse Osmosis (RO) pure water for spray drying. The dried product was designated S008-E11-09A S701NH and had a protein content of 101.02 wt% (N x 6.25.25) on a dry weight basis.

Most panelists (5/8) assessed the sample as less beany than the conventional IEP control (prepared as described in example 1) for sensory evaluation S008-E11-09A S701 NH.

Example 4

This example illustrates another method for preparing a pH adjusted soy protein isolate.

30 kg of minimally heat-treated defatted soy flour was added to 300L of 0.15M CaCl at room temperature₂To the solution, and stirred for 30 minutes to provide an aqueous protein solution. 300L of 0.075M CaCl were additionally added₂The solution was removed and the residual soy flour was removed and the resulting protein solution was clarified by centrifugation and filtration to yield 525L of filtered protein solution having a protein content of 1.32 wt%. Half the volume of water was added and the pH of the sample was lowered to 3.08 using dilute HCl. The diluted acidified protein solution was then heated at 90 ℃ for 1 minute and subsequently cooled to 50 ℃ for membrane treatment.

The diluted, acidified and heat treated protein extract solution was reduced in volume from 781.5L to 156.5L by centrifugation on a Polyethersulfone (PES) membrane having a molecular weight cutoff of 100,000 daltons. The concentration step and all subsequent membrane treatment steps were carried out at about 50 ℃. The solution was then diafiltered using 150L of Reverse Osmosis (RO) purified water, followed by further concentration to a volume of 43.5L. The solution was however diafiltered with an additional 150L of Reverse Osmosis (RO) pure water, then further concentrated to 19.5L. RO water was then added to the sample, resulting in a total mass of 72.74 kg of diluted protein solution having a protein concentration of 9.47 wt%. This represents a 99.4% yield of the initial filtered protein solution.

A30 kg sample of the diluted protein solution was adjusted to pH6 using 25% w/v aqueous sodium hydroxide and then heated to 90 ℃ for 5 minutes while mixing in a jacketed steam kettle. Upon adjustment to pH6, a large amount of protein precipitated.

The heated solution was cooled and the precipitate was allowed to settle. The soluble fraction was decanted and replaced with an equal volume of water to resuspend the solids. The slurry was allowed to settle and then the liquid phase was decanted again to remove the remaining traces of soluble fraction.

The precipitate obtained is then spray dried. The dried product was designated S010-E26-09A S701NH and had a protein content of 101.46 wt% (N x 6.25.25) on a dry weight basis.

All panelists (6/6) evaluated the sample as less beany than the conventional IEP control (prepared as described in example 1) for sensory evaluation S010-E26-09A S701 NH.

Example 5

This example illustrates another method for preparing a pH adjusted soy protein isolate.

30 kg of defatted white soybean meal was added to 300L of 0.13M CaCl at 60 deg.C₂To the solution, and stirred for 30 minutes to provide an aqueous protein solution. The residual white soybean meal was removed and the resulting protein solution was clarified by centrifugation to yield 252.4L of centrifuged protein solution having a protein content of 2.72 wt%. The clear protein solution was then added to 188.7L Reverse Osmosis (RO) pure water diafiltration at 60 ℃ and the pH of the sample was lowered to 3.38 using dilute HCl.

The volume of 420L of diluted acidified protein extract solution was reduced to 100L by centrifugation on a Polyethersulfone (PES) membrane having a molecular weight cut-off of 100,000 daltons, which was operated at a temperature of about 55 ℃. At this point, the acidified protein solution having a protein content of 4.82 wt% was diafiltered using 150L of reverse osmosis pure water, the diafiltration operation being carried out at about 56 ℃. The diafiltration solution was then concentrated to a volume of 52L and diafiltered with an additional 468L of RO water, the diafiltration operation being carried out at about 60 ℃. After this second diafiltration, the protein solution was concentrated from a protein content of 9.99 wt% to a protein content of 13.12 wt%, then diluted with water to a protein content of 6.44 wt% for spray drying or further processing. The diluted protein solution was recovered before spray drying or further processing, and the yield of the initially clear protein solution was 74.7 wt%.

A1.8 kg sample of the diluted protein solution was treated with 6M aqueous sodium hydroxide solution to raise the pH of the sample to 6.08 and form a precipitate. The sample was then lyophilized to give a product designated S023-L09-10A S701N (not fractionated). The product had a protein content of 103.47 wt% (N x 6.25.25) d.b..

Another 1.8 kg sample of the diluted protein solution was further diluted with 1.8L RO pure water and then treated with 6M aqueous sodium hydroxide solution to raise the pH of the sample to 6.00 and form a precipitate. The pH6 solution was heated to 95 ℃ for 5 minutes and then the samples were lyophilized. The dried product was designated S023-L09-10A S701NH (not fractionated) and had a protein content of 103.14 wt% (N x 6.25.25) d.b..

Example 6

This example includes an evaluation of the solubility in water of the soy protein isolates prepared by the methods of examples 2-5. Protein solubility was assessed using a modified version of the method of Morr et al, J. Food Sci. 50: 1715-1718.

A sufficient amount of protein powder to supply 0.5 g of protein was weighed into a beaker, then a small amount of Reverse Osmosis (RO) purified water was added and the mixture was stirred until a uniform paste was formed. Additional water was then added to bring the volume to about 45 ml. The beaker contents were then stirred slowly with a magnetic stirrer for 60 minutes. The pH was measured immediately after protein dispersion and adjusted to the appropriate level with dilute NaOH or HCl (2, 3, 4, 5, 6 or 7). Samples were also prepared at natural pH. For the pH adjusted samples, the pH was measured and corrected 2 times during 60 minutes of stirring. After stirring for 60 minutes, the sample was made up to a total volume of 50 ml with RO water to give a 1% protein w/v dispersion. The protein content of the dispersion was measured by combustion analysis using a Leco instrument. An aliquot of the dispersion was then centrifuged at 7,800 g for 10 minutes, which precipitated insoluble material and yielded a clear supernatant. The protein content of the supernatant was measured by Leco analysis and the protein solubility of the product was then calculated as follows: solubility (%) = (% protein in supernatant/% protein in initial dispersion) × 100.

The natural pH values of the protein isolates produced in examples 2-5 are shown in table 1 below:

TABLE 1The natural pH of a dispersion prepared at 1% protein w/v in water:

the solubility results are listed in table 2 below.

TABLE 2Solubility of the product at different pH values:

as shown by the results in table 2, the solubility of product S701N was quite large at pH 2 and 3, but not at the other pH values tested. The supplemental heat treatment to form S701NH resulted in a product that was almost completely insoluble at all pH values tested.

Example 7

This example includes an evaluation of the hydration ability of the soy protein isolate prepared by the methods of examples 2-5.

Protein powder (1 g) was weighed into a centrifuge tube (50 ml) of known weight. About 20 ml of Reverse Osmosis (RO) pure water at natural pH was then added to the powder. The centrifuge tube contents were mixed using a vortex mixer at medium speed for 1 minute. The samples were incubated at room temperature for 5 minutes and then mixed using a vortex mixer for 30 seconds. Followed by 5 more minutes incubation at room temperature followed by 30 seconds of vortexing. The sample was then centrifuged at 1,000 g for 15 minutes at 20 ℃. After centrifugation, the supernatant was carefully decanted to ensure that all solid material remained in the centrifuge tube. The centrifuge tube was then reweighed and the weight of the water-saturated sample determined.

Hydration capacity (WBC) was calculated as follows:

WBC (ml/g) = (water-saturated sample mass-initial sample mass)/(initial sample mass × sample total solids content).

The hydration ability results obtained are listed in Table 3 below

TABLE 3 hydration Capacity of the various products

As shown by the results in table 3, the addition of heat treatment in the preparation of the pH adjusted product resulted in higher hydration capacity.

Summary of the disclosure

In summary of this disclosure, the present invention provides a process for preparing a soy protein isolate having a near neutral natural pH that can replace conventional soy protein isolates in a variety of food applications. Modifications may be made within the scope of the invention.

Claims (28)

1. A soy protein product having a protein content of at least 60 wt% (N x 6.25.25) d.b.; the pH is 6; and has no beany flavor; the soy protein product has a solubility in water of greater than 89.1% at 1% protein w/v at a pH of 2-3 and a solubility in water of less than 41.4% at a pH range of 4-6, or a solubility in water of less than 13.8% at 1% protein w/v at a pH range of 2-7, wherein the solubility is determined by the protein method according to the following relationship: solubility (%) × 100 (% protein in supernatant/protein in initial dispersion).

2. The soy protein product of claim 1 having a protein content of at least 90 wt% (N x 6.25.25).

3. The soy protein product of claim 1 having a protein content of at least 100 wt% (N x 6.25.25).

4. A food composition comprising the soy protein product of any of claims 1-3.

5. A process for preparing the soy protein product of any of claims 1-3, wherein:

(a) providing an aqueous solution of a starting soy protein product having a protein content of at least 60 wt% (N x 6.25.25) d.b., being fully soluble in aqueous media at a pH below 4.4 and being heat stable at said pH range;

(b1) adjusting the pH of the solution to a pH of 6 to precipitate soy protein therefrom; and

(c1) drying all pH adjusted samples; or recovering and drying the precipitated material,

wherein the soy protein product produced has a solubility in water of greater than 89.1% at a pH of 2-3 and a solubility in water of less than 41.4% at a pH range of 4-6;

or

(a) Providing an aqueous solution of a starting soy protein product having a protein content of at least 60 wt% (N x 6.25.25) d.b., being fully soluble in aqueous media at a pH below 4.4 and being heat stable at said pH range;

(b2) adjusting the pH of the solution to pH6 to precipitate soy protein therefrom; and

(c2) heat treating the pH adjusted solution and then drying the entire pH adjusted sample; or heat treating the pH-adjusted solution, and then recovering and drying the precipitated material,

wherein the soy protein product produced has a solubility in water of less than 13.8% over a pH range of 2 to 7.

6. The method according to claim 5, characterized in that the heat treatment is carried out at a temperature of 70-160 ℃ for 2 seconds-60 minutes.

7. The method according to claim 6, characterized in that the heat treatment is carried out at a temperature of 80-120 ℃ for 15 seconds-15 minutes.

8. The method according to claim 7, characterized in that the heat treatment is carried out at a temperature of 85-95 ℃ for 1-5 minutes.

9. The method according to any one of claims 5 to 8, characterized in that the aqueous solution of the starting soy protein product is prepared by:

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

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

(c) optionally diluting said aqueous soy protein solution,

(d) adjusting the pH of the aqueous soy protein solution to 1.5-4.4 to produce an acidified clear soy protein solution, and

(e) the clarified aqueous soy protein solution is concentrated using a selective membrane technique while maintaining the ionic strength constant.

10. The method according to claim 9, characterized in that the aqueous calcium salt solution is an aqueous calcium chloride solution.

11. The method according to claim 9, wherein the pH of the aqueous soy protein solution is adjusted to pH 2-4.

12. The method according to claim 10, wherein the pH of the aqueous soy protein solution is adjusted to pH 2-4.

13. The method of claim 9 wherein the acidified clear soy protein solution is heat treated to reduce the activity and microbial load of the anti-nutritional inhibitor prior to the concentrating step.

14. The process of any one of claims 10 to 12, wherein prior to the concentration step, the acidified clear soy protein solution is heat treated to reduce the activity of anti-nutritional inhibitors and microbial load.

15. The method of claim 9 wherein said concentrated soy protein solution is diafiltered.

16. The process of any one of claims 10 to 13 wherein the concentrated soy protein solution is diafiltered.

17. The method of claim 14 wherein said concentrated soy protein solution is diafiltered.

18. The method of claim 9 wherein the concentrated soy protein solution is pasteurized to reduce the microbial load.

19. The method of any one of claims 10-13, 15 and 17, wherein the concentrated soy protein solution is pasteurized to reduce the microbial load.

20. The method of claim 16 wherein the concentrated soy protein solution is pasteurized to reduce the microbial load.

21. A soy protein product produced by the process of claim 5.

22. A soy protein product produced by the process of claim 9.

23. A soy protein product produced by the process of claim 14.

24. A soy protein product produced by the process of claim 16.

25. A soy protein product produced by the process of claim 19.

26. A soy protein product produced by the process of any one of claims 6 to 8, 10 to 13, 15, 17-18 and 20.

27. A food composition comprising the soy protein product of any of claims 21-25.

28. A food composition comprising the soy protein product of claim 26.