HK1166243B - Preparation of soy protein product using water extraction ("s803") - Google Patents

Description

Preparation of soy protein products with water extraction ("S803")

Reference to related applications

The present application claims priority from U.S. provisional patent application No. 61/202,260 filed on 11/2/2009 and U.S. provisional patent application No. 61/272,288 filed on 8/9/2009 under 35USC 119 (e).

Technical Field

The present invention relates to the preparation of soy protein products.

Background

The preparation of a soy protein product, preferably a soy protein isolate, which is fully soluble and capable of providing a transparent and heat stable solution at low pH values is described in 61/107,112 (7865-. The soy protein product can be used for protein fortification of, inter alia, soft drinks and sports drinks and other acidic aqueous systems without protein precipitation. The soy protein product was prepared as follows: the pH of the aqueous soy protein solution is adjusted to a pH of about 1.5 to about 4.4 (preferably about 2.0 to about 4.0) by extracting the soy protein source with an aqueous calcium chloride solution at natural pH, optionally diluting the resulting aqueous soy protein solution to produce an acidified clear soy protein solution, which may optionally be concentrated and/or diafiltered before drying.

Summary of The Invention

It has now been surprisingly found that soy protein products of comparable properties can be formed by a process which comprises extracting a soy protein source with water without the need to use calcium chloride.

In one aspect of the invention, the soy protein source material is extracted with water at low pH and the resulting aqueous soy protein solution is subjected to ultrafiltration and optionally diafiltration to provide a concentrated and optionally diafiltered soy protein solution, which may be dried to provide a soy protein product.

The present invention provides a soy protein product having a protein content of at least about 60 wt% (N x 6.25) d.b. and being soluble at acidic pH values to provide a clear and heat stable aqueous solution thereof. The soy protein product is useful for protein fortification of, inter alia, soft drinks and sports drinks, as well as other aqueous systems, without precipitation of protein. The soy protein product is preferably an isolate having a protein content of at least about 90 wt%, preferably at least about 100 wt% (N x 6.25) d.b..

According to one aspect of the present invention, there is provided a method of producing a soy protein product having a soy protein content of at least about 60% by weight on a dry weight basis (d.b.), the method comprising:

(a) extracting the soy protein source with water at low pH to cause solubilization of 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) concentrating the soybean protein water solution by using a selective membrane technology,

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

(e) optionally drying the concentrated soy protein solution.

The soy protein product is preferably an isolate having a protein content of at least about 90 wt%, preferably at least about 100 wt% (N x 6.25) d.b..

Although the present invention is primarily directed to the production of soy protein isolates, it is contemplated that soy protein products having a lower purity can be provided that have properties similar to soy protein isolates. Such lower purity preparations may have a protein concentration of at least about 60 wt% (N × 6.25) d.b..

The novel soy protein product of the present invention can be blended with solid beverages (powdered drinks) for forming aqueous soft drinks or sports drinks by dissolving it in water. Such a blend may be a powdered beverage.

The soy protein product provided by the present invention can be provided as an aqueous solution thereof that has high clarity at acidic pH values and is heat stable at these pH values.

In another aspect of the present invention, there is provided an aqueous solution of a soy product provided by the present invention, which solution is stable to heat at low pH. The aqueous solution may be a beverage, which may be a clear beverage in which the soy protein product is completely soluble and transparent, or an opaque beverage in which the soy protein product does not increase opacity. Aqueous solutions of soy protein products also have excellent solubility and clarity at pH 7.

The soy protein products produced according to the methods herein do not have the characteristic beany flavor of soy protein isolates and are suitable not only for protein fortification of acidic media, but also for use in a wide variety of conventional applications of protein isolates, including but not limited to protein fortification of processed foods and beverages, emulsification of oils, as body formers in baked goods, and foaming agents in gas-entrapped products. Additionally, soy protein products can be made into protein fibers, can be used 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 supplements. Other uses of soy protein products are in pet food, animal feed and in industrial and cosmetic applications as well as in personal care products.

Summary of the invention

The first step of the process for providing a soy protein product comprises solubilizing soy protein from a soy protein source. The soy protein source may be soy or any soy product or by-product obtained from soy processing, including but not limited to soy meal, soy flakes (soy flakes), soy meal (soy grits), 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 appreciable amounts of fat, a degreasing step is typically required during the treatment process. 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 native protein.

The present invention achieves protein solubilization from soy protein source material with water at low pH. The extraction may be carried out at a pH of from about 1.5 to about 3.6, preferably at a pH that matches the pH of the preparation (e.g., beverage) in which the protein preparation is to be incorporated, e.g., a pH of from about 2.6 to about 3.6. Typically, water is added to the soy protein source and the pH is then adjusted by the addition of any suitable food grade acid (typically hydrochloric or phosphoric acid). Non-food grade chemicals may be used when the soy protein product is intended for non-food use.

In batch processing, the solubilization of the protein is carried out at a temperature of from about 1 ℃ to about 100 ℃, preferably from about 15 ℃ to about 35 ℃, preferably with agitation to reduce the solubilization time, which is typically from about 1 to about 60 minutes. Solubilization is preferably performed to substantially extract as much protein from the soy protein source as is practicable to provide an overall high product yield.

In the continuous process, the extraction of soy protein from the soy protein source is carried out in any manner consistent with carrying out a continuous extraction of soy protein from the soy protein source. In one embodiment, the soy protein source is continuously mixed with water and the mixture is passed through a pipe or conduit having a length and at a flow rate for a residence time sufficient to effect the desired extraction consistent with the parameters described herein. In such a continuous process, the solubilization step is carried out rapidly over a period of up to about 10 minutes, preferably to effect solubilization to substantially extract as much protein from the soy protein source as is practicable. Dissolution in a continuous process is carried out at a temperature of between about 1 ℃ and about 100 ℃, preferably between about 15 ℃ and about 35 ℃.

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

The protein extraction step may have the additional effect of dissolving fat that may be present in the soy protein source, which in turn results in fat being present in the aqueous phase.

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

Antioxidants may be present during the extraction step. The antioxidant may be any suitable antioxidant, for example sodium sulfite or ascorbic acid. The amount of antioxidant employed may vary from about 0.01% to about 1% by weight of the solution, preferably about 0.05% by weight. 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 suitable manner, such as by employing a decanter centrifuge, 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 proteins, such as by conventional isoelectric precipitation methods or any other suitable method to recover such residual proteins.

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, the disclosures of which are incorporated herein by reference, assigned to the assignee hereof, the defatting step described herein can be performed on the isolated aqueous protein solution. Alternatively, the defatting of the separated aqueous protein solution may be achieved by any other suitable method.

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 suitable conditions, typically at 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 may be removed from the soy protein solution by any suitable method, for example by filtration.

The clear acidified aqueous soy protein solution may be subjected to a heat treatment to inactivate thermolabile antinutritional factors, such as trypsin inhibitors, which are present in the aqueous soy protein solution as a result of extraction from the soy protein source material during the extraction step. This heating step also provides the additional benefit of reducing the microbial load. Typically, the protein solution is heated to a temperature of about 70 ℃ to about 120 ℃, preferably about 85 ℃ to about 95 ℃, for about 10 seconds to about 60 minutes, preferably about 30 seconds to about 5 minutes. The heat treated soy protein solution may then be cooled to a temperature of from about 2 ℃ to about 60 ℃, preferably from about 20 ℃ to about 35 ℃, for further processing as described below.

If the purity is sufficient, the resulting aqueous soy protein solution may be directly dried to produce a soy protein product. To reduce the impurity content, the aqueous soy protein solution may be treated prior to drying.

The aqueous soy protein solution may be concentrated to increase its protein concentration while maintaining its ionic strength substantially constant. Such concentrations are typically achieved to provide a concentrated soy protein solution having a protein concentration of from about 50 to about 400g/L, preferably from about 100 to about 250 g/L.

The concentration step may be carried out in any suitable manner consistent with batch or continuous operation, for example by employing any suitable selective membrane technique such as ultrafiltration or diafiltration, which is sized to allow the desired degree of concentration as the aqueous protein solution passes through the membrane, depending on the different membrane materials and configurations, and for continuous operation, using membranes 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, such as hollow fibre membranes or spiral wound membranes.

It is well known that ultrafiltration and similar selective membrane techniques allow low molecular weight species to pass through while preventing higher molecular weight species from passing through the membrane. The low molecular weight substances extracted from the source material include saccharides, pigments, low molecular weight proteins, and anti-nutritional factors such as trypsin inhibitors which are low molecular weight proteins themselves. 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, depending on the membrane material and structure.

The soy protein solution may be subjected to a diafiltration step using water, either before or after complete concentration. The water may be at its natural pH or at a pH equal to the pH of the protein solution being diafiltered or any pH in between. Such 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, additional quantities of contaminants are removed from the aqueous soy protein solution by passing the permeate through a membrane. 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 has been sufficiently purified so as to provide, on drying, a product having the desired protein content, preferably an isolate having a protein content of greater than 90% by weight (N × 6.25) (dry basis). This diafiltration may be performed 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, e.g. 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, depending on the membrane material and configuration.

The concentration step and diafiltration step herein may be effected in such a way that the soy protein product subsequently recovered by drying the concentrated and diafiltered retentate contains less than about 90% by weight protein (N x 6.25) d.b., for example at least about 60% by weight protein (N x 6.25) d.b. By partially concentrating and/or partially diafiltering the aqueous soy protein solution, it is possible to remove the contaminants only partially. The 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 a portion of the diafiltration step. The antioxidant may be any suitable antioxidant, for example 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% by weight, preferably about 0.05% by weight. 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 suitable temperature (typically from about 2 ℃ to about 60 ℃, preferably from about 20 ℃ to about 35 ℃, and for a period of time that results in the desired degree of concentration and diafiltration.

There are two major trypsin inhibitors in soybean, the Kunitz inhibitor, 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 various process variables.

As described above, heat treatment of acidified aqueous soy protein solutions can be used to inactivate thermolabile trypsin inhibitors. This heat treatment may also be applied to the concentrated and optionally diafiltered soy protein solution.

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

The activity of trypsin inhibitors can be reduced by acidifying and membrane treating the diluted protein solution at a lower pH (e.g., about 1.5 to about 3) relative to treating the solution at a higher pH (e.g., about 3 to about 3.6). When the protein solution is concentrated and diafiltered 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 about pH3, by the addition of any suitable food grade base, for example sodium hydroxide.

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

This addition of the reducing agent can be achieved at different stages of the overall process. The reducing agent may be added with the soy protein source material in 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, or may be dry blended with the dried soy protein product. As described above, the addition of the reducing agent may combine the heat treatment step and the film treatment step.

If it is desired to retain active trypsin inhibitors in the concentrated protein solution, this can be achieved as follows: 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., about 3 to about 3.6) without the use of a reducing agent, using smaller pore size concentration and diafiltration membranes, operating the membranes at lower temperatures and using smaller volumes of diafiltration media.

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

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 suitable conditions, typically at 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 suitable method, for example by filtration.

The concentrated and optionally diafiltered aqueous soy protein solution may be dried by any suitable technique, such as spray drying or freeze drying. The soy protein solution may be subjected to a pasteurization step prior to drying. Such pasteurization may be carried out 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 is then cooled for drying, preferably to a temperature of from 15 ℃ to about 35 ℃.

The protein content of the dry soy protein product is at least about 60 wt%, preferably more than about 90 wt% protein, more preferably at least about 100 wt% (N x 6.25) d.b..

The soy protein product produced by the present invention is soluble in an acidic aqueous environment, making the product ideal for incorporation into both 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 by the present invention can be added to such beverages in any suitable amount to provide protein fortification to such beverages, for example, at least about 5g of soy protein per serving. The added soy protein product dissolves in the beverage and does not impair the clarity of the beverage, even after heat treatment. The soy protein product may be blended with the dried beverage prior to reconstitution of the beverage by dissolution in water. In some instances, it may be desirable to modify the normal beverage formulation to accept the composition of the present invention when the presence of components in the beverage may adversely affect the ability of the composition of the present invention to remain dissolved in the beverage. In addition, soy protein products are highly soluble and produce solutions of excellent clarity at pH 7.

Examples

Example 1:

this example evaluates the extraction ability of defatted, minimally heat treated soy flour at low pH with water or brine.

With the pH of the extraction system adjusted to 3 with dilute HCl, water, 0.15 NaCl or 0.15M CaCl₂(100ml) defatted, minimally heat treated soy flour (10g) was extracted. The powder and solvent were mixed, the pH was adjusted, and then the sample was stirred with a magnetic stir bar and stir plate for 30 minutes at room temperature. The extract was separated from the defatted meal (ent meal) by centrifugation at 10,200g for 10 minutes and then further clarified by filtration through a syringe filter with a 0.45 μm pore size. The protein content of the filtrate was measured with a LECO FP528 nitrogen determinator then the sample was diluted with an equal volume of water and observed for the presence of precipitate.

The results of the extraction capacity are given in table 1 below:

TABLE 1Effect of extraction solvent on protein content of pH3 extract

Sample (I)	% protein	Extraction Capacity (%)
			Water (W)	3.38	62.2
Sodium chloride	2.94	54.1
			Calcium chloride	3.79	69.8

As can be seen from the results in table 1, the extraction capacity of all solvents is quite high, the calcium chloride solution dissolving the most protein. Extraction with water alone dissolved more protein than extraction with 0.15M sodium chloride solution.

When the clarified extract is diluted with water, the sodium chloride extract precipitates heavily, while the water and calcium chloride extracts remain substantially clear.

Example 2:

this example investigates the extraction capacity of soy flour with water at various pH values and the clarity of the resulting extract when acidified to pH 3.

Defatted, minimally heat treated soy flour (10g) was extracted with reverse osmosis purified water (100ml) using a magnetic stir bar/stir plate operating at a constant speed for 30 minutes at room temperature. Extraction was carried out for 30 minutes, and a timer was started from the start of stirring. Immediately after the meal was completely wet (which occurred quite quickly), the pH of the extract (water plus meal) was adjusted to 3, 5, 7, 9 or 11 with 6M hcl or 6M NaOH, and the pH of the extract was monitored and corrected throughout the 30 minute extraction. After 30 minutes, the sample was centrifuged at 10,200g for 10 minutes to separate the extract from the defatted flour. The extract was then further clarified by filtration through a 0.45 μm pore size syringe filter. The protein content of the filtered extract was evaluated using a LECO FP528 nitrogen determinator. The pH and clarity of the filtered extract were also determined (a 600). The filtered extract samples were diluted with one portion of reverse osmosis purified water and the diluted samples were evaluated for pH and clarity. The full strength and diluted samples were then adjusted to pH3 with 6M HCl or 6M NaOH as needed and the clarity was re-evaluated.

The effect of extraction pH on the ability to extract soy flour with water is given in table 2 below:

TABLE 2Effect of pH on the ability to extract Soy flour with Water

pH of extraction	% protein of the extract	Extraction Capacity (%)
			3	2.43	45.4

[0069]

5	0.70	13.1
			7	4.05	75.7
9	4.28	80.0
			11	5.18	96.8

As can be seen from the results of table 2, significant extraction capacity was obtained with water at alkaline pH. Although lower, the extraction capacity obtained at pH3 is a reasonable value.

The effect of acidification on the clarity of the full strength extract samples is given in table 3 below:

TABLE 3Effect of acidification on the full strength aqueous extract

pH of extraction	Initial pH	Initial A600	Adjusted pH	Final A600
					3	2.88	0.089	2.96	0.095
5	4.99	0.007	3.05	2.58
					7	6.96	0.155	3.04	＞3.0
9	8.87	0.222	3.02	＞3.0
					11	10.92	0.173	2.95	＞3.0

As can be seen from the results in table 3, the sample extracted at pH3 was the only sample that remained clear after pH adjustment.

The effect of acidification on the clarity of the diluted extract samples is given in table 4 below:

TABLE 4-acidifying para-xyleneEffect of clarity of released Water extract

pH of extraction	Initial pH	Initial A600	Adjusted pH	Final A600
					3	2.97	0.222	----	----
5	5.06	0.001	2.96	2.53
					7	6.97	0.080	3.02	＞3.0
9	8.80	0.129	2.97	0.334
					11	10.86	0.062	2.96	1.55

As can be seen from the results in table 4, the samples extracted at pH3 and then diluted were the clearest of the samples evaluated.

Example 3:

this example was conducted to determine if the low pH aqueous extract of soy flour remained clear upon concentration and diafiltration and could also be rehydrated clear after drying.

80g of defatted, minimally heat treated soy flour was added to 800ml of reverse osmosis purified water at ambient temperature and stirred for 30 minutes to provide an aqueous protein solution. Immediately after dispersing the meal into water, the pH of the system was adjusted to 3 by adding dilute HCl. The pH was monitored and corrected to 3 periodically during the 30 minute extraction. The residual soy flour was removed and the resulting protein solution was clarified by centrifugation and filtration to yield 475ml of a filtered protein solution having a protein content of 1.86% by weight.

The filtered protein solution volume was reduced to 42ml by concentration through a Polyethersulfone (PES) membrane with a molecular weight cut-off of 10,000 daltons. An aliquot of 40ml of the concentrated protein solution was diafiltered with 80ml of reverse osmosis purified water. The protein content of the resulting diafiltered, concentrated protein solution was 15.42% by weight and represents a yield of 69.2% by weight of the initial filtered protein solution. The diafiltered, concentrated protein solution was then dried to yield the product found to have a protein content of 90.89% (N × 6.25) w.b.. This product is named S803.

A 3.2 wt% protein solution in water was prepared S803 and Color and clarity were evaluated using a HunterLab Color Quest XE instrument operating in transmission mode.

The color and clarity values are given in table 5 below:

TABLE 5HunterLab score of 3.2% protein solution of S803

Sample (I)	L*	a*	b*	Haze (%)
					S803	96.97	-1.39	10.87	17.6

As can be seen from table 5, the color of the S803 solution was very light and the haze level was rather low.

Example 4:

in this example, the thermal stability of the S803 article produced according to the method of example 3 was evaluated.

A2% w/v aqueous protein solution of S803 was produced. The pH of the solution was measured with a pH meter and the clarity of the solution was assessed by turbidity measurements with a HunterLab Color Quest XE instrument. The solution was then heated to 95 ℃ and held at this temperature for 30 seconds, followed immediately by cooling to room temperature in an ice bath. The clarity of the heat-treated solution was then measured.

The pH of the S803 solution was 2.91. The clarity of the protein solution before and after heating is given in table 6 below:

TABLE 6Effect of Heat treatment on clarity of the S803 solution

Sample (I)	Haze (%)
		Before heating	53.8
After heating	32.4

As can be seen from table 6, the clarity of the 2% solution of S803 was inferior to the 3.2% solution prepared in example 3. The reason for this is unknown. In any case, the haze level of the sample decreased when the 2% protein solution was heat treated. Thus, the heat treatment does not impair the clarity.

Example 5:

in this example, the preparation of S803 was scaled up from bench to pilot plant scale.

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

The filtered protein solution volume was reduced to "e" L by concentration through an "f" membrane with a molecular weight cut-off of "g" daltons. An aliquot of the "h" L concentrated protein solution was dried to obtain a product having a protein content of "k"% (N × 6.25) d.b., which solution had a protein content of "i"% by weight and represents the yield of "j"% by weight of the initial filtered protein solution. This product is named "l" S803-02. The remaining "m" L of concentrated protein solution was diafiltered with "n" L of reverse osmosis purified water "o". The protein content of the resulting diafiltered, concentrated protein solution was "p"% by weight and represents the yield of "q"% by weight of the initial multi-filtered protein solution. The diafiltered, concentrated protein solution was then dried to obtain a product with a protein content of "r"% (N × 6.25) d.b.. This product is designated "l" S803.

The parameters "a" to "r" of the two runs are given in table 7 below:

TABLE 7Parameters for operating to produce S803

l	S005-L16-08A	S005-A20-09A
			a	20	20
b	200	200
			c	170	210
d	0.71	0.91
			e	18.46	25
f	PVDF	PVDF
			g	5000	5000
h	2	0
			i	6.21	n/a
j	9.9	n/a
			k	95.96	n/a
m	16.46	25
			n	34	50
o	Adjusted to pH3 with dilute HCl	Natural pH
			p	6.29	8.69
q	86.0	93.2
			r	94.63	98.36

not applicable n/a

A3.2% w/v protein solution of S005-L16-08A S803, S803-02 and S005-A20-09A S803 was prepared in water and Color and clarity evaluated with a Hunter Lab Color Quest XE instrument operating in transmission mode. The pH was also measured with a pH meter.

The pH, color and clarity values are given in table 8 below:

TABLE 8pH and HunterLab fraction of 3.2% protein solutions of-S005-L16-08A S803, S803-02 and S005-A20-09A S803

As can be seen from table 8, the color of the S803 solution was very light and the haze level was low.

The Color of the dry powder was also evaluated in reflectance mode using a HunterLab Color Quest XE instrument. The color values are given in table 9 below:

TABLE 9HunterLab score of-S005-L16-08A S803, S803-02 and S005-A20-09A S803 Dry powders

As can be seen from table 9, all dry products were very light in color.

Example 6:

this example includes evaluating the thermal stability in water of the soy protein isolate produced by the method of example 5 (S803).

A2% w/v protein solution of S005-L16-08A S803 and S005-A20-09A S803 was produced in water and the pH was adjusted to 3. The clarity of these solutions was evaluated by measuring the turbidity in transmission mode with a HunterLab Color Quest XE instrument. The solution was then heated to 95 ℃, held at this temperature for 30 seconds and then immediately cooled to room temperature in an ice bath. The clarity of the heat treated solution was then measured again.

The clarity of the protein solution before and after heating is given in table 10 below:

watch 10Effect of Heat treatment on clarity of solutions S005-L16-08A S803 and S005-A20-09A S803

As can be seen from the results of table 10, the clarity of these 2% solutions of S803 prepared on a pilot scale as described in example 5 is much better than the clarity of the 2% solution of S803 prepared on a laboratory scale as described in example 3. The reason for this difference is unknown. As in the case of example 4, the S803 solution was found to be stable to heat and the heat treatment seemed to improve the clarity.

Example 7:

this example includes evaluating the solubility in water of the soy protein isolate produced by the method of example 5 (S803). The solubility was determined based on protein solubility (referred to as the protein method, a modified version of the method in J.food Sci.50: 1715-1718 by Morr et al) and total product solubility (referred to as the precipitation method).

Protein powder sufficient to provide 0.5g of protein was weighed into a beaker, then a small amount of Reverse Osmosis (RO) purified water was added and the mixture stirred until a well-kneaded dough was formed (smooth paste). Additional water was then added to bring the volume to approximately 45 ml. The contents of the beaker were then stirred slowly with a magnetic stirrer for 60 minutes. Immediately after dispersing the protein, the pH is measured and adjusted to the appropriate level (2, 3,4, 5, 6 or 7) with dilute NaOH or HCl. Samples were also prepared at natural pH. For the pH adjusted samples, the pH was measured and corrected twice during 60 minutes of stirring. After stirring for 60 minutes, the sample was made up to a total volume of 50ml with RO water to give a 1% w/v protein dispersion. The protein content of the dispersion was measured with a LECO FP528 nitrogen determinator. An aliquot (20ml) of the dispersion was transferred to a pre-weighed centrifuge tube which had been oven dried overnight at 100 ℃, then cooled in a desiccator and the tube capped. The sample was centrifuged at 7800g for 10 minutes, which sedimented insoluble material and yielded a clear supernatant. The protein content of the supernatant was measured by LECO analysis, then the supernatant and tube cap were discarded and the precipitated material was dried overnight in an oven set at 100 ℃. The next morning the tubes were transferred to a desiccator and allowed to cool. The weight of dry precipitated material was recorded. The dry weight of the initial protein powder was calculated by multiplying the weight of the powder used by a factor ((100-powder water content (%)/100). The solubility of the product was then calculated in two different ways:

1) solubility (protein method) (%) -% (protein in supernatant/% protein in initial dispersion) × 100

2) Solubility (precipitation method) (%) × (1- (weight of dry insoluble precipitation material/((weight of 20ml dispersion/weight of 50ml dispersion) × initial weight of dry egg white powder)) × 100 @ 1 @ dry insoluble precipitation material) (%) × 100

The natural pH values of the protein isolates produced in example 5 in water (1% protein) are shown in table 11:

TABLE 11Natural pH of a solution prepared with 1% protein in water

Batches of	Product(s)	Natural pH
			S005-L16-08A	S803	3.36
S005-A20-09A	S803	3.14

The solubility results obtained are given in tables 12 and 13 below:

TABLE 12Solubility of S803 at different pH values based on the protein method

Watch 13Solubility of S803 at different pH values based on the precipitation method

As can be seen from the results of tables 12 and 13, the S803 product is very soluble at pH values of 2, 3 and 7 as well as at natural pH.

Example 8:

this example includes evaluating the clarity in water of the soy protein isolate produced by the method of example 5 (S803).

The clarity of a 1% w/v protein dispersion prepared as described in example 7 was assessed by measuring the absorbance at 600nm, with lower absorbance fractions indicating higher clarity. Analysis of the samples in transmission mode on a HunterLab Color Quest XE instrument also provides a percent haze reading, another measure of clarity.

The clarity results are given in tables 14 and 15 below:

TABLE 14Clarity of the S803 solution at different pH values evaluated by A600

TABLE 15 clarity of S803 solutions at different pH values as assessed by HunterLab analysis

As can be seen from the results of tables 14 and 15, the S803 solution showed excellent clarity at pH values of 2, 3 and 7 and at natural pH.

Example 9:

this example includes assessing the solubility of the soy protein isolate produced by the method of example 5 (S803) in soft drinks (Sprite) and sports drinks (Orange Gatorade). Solubility was measured by adding protein to the beverage, without correcting the pH and again adjusting the pH of the protein fortified beverage to the level of the original beverage.

When solubility was assessed without correction of pH, an amount of protein powder sufficient to provide 1g of protein was weighed into a beaker, a small amount of beverage was added and stirred until a well-kneaded dough was formed. The additional beverage was added to bring the volume to 50ml and the solution was then stirred slowly on a magnetic stirrer for 60 minutes to obtain a dispersion of 2% protein w/v. Samples were analyzed for protein content using a LECO FP528 nitrogen determinator then aliquots of the protein containing beverages were centrifuged at 7800g for 10 minutes and the protein content of the supernatant measured.

Solubility (%) - (% protein in supernatant/% protein in initial dispersion) × 100

When assessing solubility with pH correction, the pH of the protein-free soft drink (sprite) was measured (3.39) and the pH of the sports drink (orange gadale) (3.19). An amount of protein powder sufficient to provide 1g of protein was weighed into a beaker and a small amount of beverage was added and stirred until a well-kneaded dough was formed. The other beverage was added to bring the volume to approximately 45ml and the solution was then stirred slowly on a magnetic stirrer for 60 minutes. The pH of the beverage containing the protein was measured and then adjusted with HCl or NaOH as needed to the pH originally without the protein. The total volume of each solution was then brought to 50ml with additional beverage, resulting in a 2% protein w/v dispersion. Samples were analyzed for protein content using a LECO FP528 nitrogen determinator then aliquots of the protein containing beverages were centrifuged at 7800g for 10 minutes and the protein content of the supernatant measured.

Solubility (%) - (% protein in supernatant/% protein in initial dispersion) × 100

The results obtained are given in table 16 below:

TABLE 16Solubility of S803 in sprite and orange gadale

As can be seen from the results of table 16, S803 was very soluble in the snow-bi and orange gadale. Since S803 is an acidified product, the addition of protein has little effect on the pH of the beverage.

Example 10:

this example includes evaluating the clarity of the soy protein isolate produced by the method of example 5 (S803) in soft drinks and sports drinks.

The clarity of the 2% w/v protein dispersions prepared in soft drinks (sprite) and sports drinks (orange gadale) of example 9 was assessed using the method described in example 8. For absorbance measurements at 600nm, the spectrophotometer was blanked with the appropriate beverage before the measurements were taken.

The results obtained are given in tables 17 and 18 below:

TABLE 17Clarity of S803 in snow Bian and orange Jiadele (A600)

Watch 18S803 HunterLab turbidity readings in sprite and orange Grace

As can be seen from the results of tables 17 and 18, S005-L16-08A S803 increased turbidity in orange Graham much more than S005-A20-09A S803. The reason for this is unknown. When both S803 products were added to the sprite, the beverage was substantially clear or possibly slightly cloudy.

Summary of the disclosure

In summary of the present disclosure, the present invention provides a method for producing a soy protein product soluble in an acidic medium based on water extraction of a soy protein source material. Modifications are possible within the scope of the invention.

Claims (27)

1. A process for preparing a soy protein product having a soy protein content of at least 60 wt% on a dry weight basis, nx 6.25, and being soluble and clear at a pH of 7, characterized in that:

(a) extracting a soy protein source with water at a pH of 1.5 to 3.6 to solubilize 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) concentrating the aqueous soy protein solution using a selective membrane technique,

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

(e) drying the concentrated and optionally diafiltered soy protein solution.

2. The method of claim 1, characterized in that the pH of the water is 2.6 to 3.6.

3. The method of claim 1, characterized in that the extraction step is carried out at a temperature of 15 ℃ to 35 ℃.

4. The method of claim 1, characterized in that the protein concentration of the aqueous soy protein solution is 5-50 g/L.

5. The method of claim 4, characterized in that the protein concentration of the aqueous soy protein solution is 10-50 g/L.

6. The method of claim 1, characterized in that the water comprises an antioxidant.

7. The process of claim 1 characterized in that the aqueous soy protein solution is treated with an adsorbent to remove color and/or odor compounds from the aqueous soy protein solution.

8. The process of claim 1, characterized in that the aqueous soy protein solution is subjected to a heat treatment at a temperature of 70 ℃ to 120 ℃ for 10 seconds to 60 minutes to inactivate heat-labile anti-nutritional factors, and wherein the heat treatment step further optionally pasteurizes the clarified aqueous protein solution.

9. The method of claim 8, characterized in that the heat treatment step is carried out at a temperature of 85 ℃ to 95 ℃ for 30 seconds to 5 minutes.

10. The process according to claim 9, characterized in that the heat-treated soy protein solution is cooled to a temperature of 2 ℃ to 60 ℃ for further processing.

11. The process of claim 1, characterized in that the aqueous soy protein solution is concentrated to a protein concentration of 50-400 g/L.

12. The method as set forth in claim 11, characterized in that the aqueous soybean protein solution is concentrated to a protein concentration of 100 and 250 g/L.

13. The process of claim 11 characterized in that said soy protein solution is subjected to said optional diafiltration step using 2 to 40 volumes of diafiltration solution using water or acidified water before or after complete concentration of said soy protein solution.

14. The process according to claim 11, characterized in that the optional diafiltration step is carried out at least partly in the presence of an antioxidant.

15. The process of claim 11, characterized in that said optional diafiltration step is performed.

16. The process of claim 13 characterized in that said optional diafiltration step is effected optionally at least partially in the presence of an antioxidant until no significant further amount of contaminants or visible colour is present in the permeate and until the retentate has been sufficiently purified so as to provide, when dried, a soy protein product having a protein content of at least 60% by weight, N x 6.25, d.b..

17. The process according to claim 13, characterized in that the concentration step and/or the optional diafiltration step are carried out at a temperature of 2 ℃ to 60 ℃ with a membrane having a molecular weight cut-off of 3,000 to 1,000,000 daltons.

18. The process of claim 11, characterized in that the concentration and/or optional diafiltration step is operated in a manner that facilitates removal of trypsin inhibitors.

19. The process of claim 11, characterized in that prior to said drying step, said concentrated and optionally diafiltered soy protein solution is treated with an adsorbent to remove colour and/or odour compounds; and/or pasteurizing the concentrated and optionally diafiltered soy protein solution by heating at a temperature of 55 ℃ to 70 ℃ for 30 seconds to 60 minutes before drying.

20. The process of claim 19, characterized in that the pasteurized, concentrated and optionally diafiltered soy protein solution is cooled to a temperature of 15 ℃ to 35 ℃ for drying or further processing.

21. The process of claim 11, characterized in that a reducing agent is present during (a) the extraction step and/or (b) the concentration and/or optional diafiltration step, and/or is added to (c) the concentrated and optionally diafiltered soy protein solution prior to drying and/or (d) the dried soy protein product to break or rearrange the disulfide bonds of trypsin inhibitors to reduce trypsin inhibitor activity.

22. The process of any one of claims 1 to 21, characterized in that the concentrated and optionally diafiltered soy protein solution is dried to provide a soy protein product having a protein content of 60-90% by weight, N x 6.25, d.b.

23. The process of any one of claims 1 to 21, characterized in that the concentrated and optionally diafiltered soy protein solution is dried to provide a soy protein product having a protein content of at least 90% by weight, N x 6.25, d.b..

24. The process of any one of claims 1 to 21, characterized in that the concentrated and optionally diafiltered soy protein solution is dried to provide a soy protein product having a protein content of at least 100% by weight, N x 6.25, d.b..

25. A soy protein product prepared by the process of any of claims 1-24.

26. The soy protein product of claim 25 which is blended with a water-soluble powder material for preparing an aqueous solution of the blend.

27. The soy protein product of claim 25 which is a powdered beverage.