pH adjusted soy protein isolate and uses

Abstract

pH-adjusted soy protein products, particularly isolates, that have a natural pH of about 6 and have a non-beany flavor are provided by the processing of soy protein product which is completely soluble in aqueous media at a pH of less than about 4.4 and heat stable in this pH range or a concentrated soy protein solution produced in the preparation of such soy protein product.

Claims

1. A soy protein product of having a protein content of at least about 60 wt % (N6.25) d.b. with a pH of 5.31 in water at 1% w/v and which has a non-beany flavor, the soy protein product having a solubility at 1% protein w/v of 89.1% in water at pH 2, 100% in water at pH 3, 41.4% in water at pH 4, 5.4% in water at pH 5 and 31.3% in water at pH 6, wherein the solubility is determined by the protein method, in accordance with the relationship: solubility (%)=(% protein in supernatant/% protein in initial dispersion)100.

2. A soy protein product having a protein content of at least about 60 wt % (N6.25) d.b. with a pH of 5.86 in water at 1% w/v and which has a non-beany flavor, the soy protein product having a solubility in water at 1% protein w/v of 13.8% at pH 2, 5.5% at pH 3, 4.0% at pH 4, 0% at pH 5, 11.7% at pH 6 and 9.0% at pH 7, wherein the solubility is determined by protein method, in accordance with the relationship: solubility (%)=(% protein in supernatant/% protein in initial dispersion)100.

3. The soy protein product of claim 1 or 2 which has a protein content of at least about 90 wt % (N6.25).

4. The soy protein product of claim 3 which has a protein content of at least about 100 wt % (N6.25).

5. A food composition comprising a soy protein product as claimed in claim 1 or 2.

6. A method of producing a soy protein product, which comprises: providing an aqueous solution of a soy protein product having a protein content of at least about 60 wt % (N6.25) d.b. which is completely soluble in aqueous media at a pH of less than about 4.4 and heat stable at that pH range, adjusting the pH of the solution to about pH 6 to precipitate soy protein therefrom, and optionally drying the pH adjusted solution including the precipitated soy protein or optionally recovering and drying the precipitated soy protein or optionally heat treating the pH-adjusted solution including the precipitated soy protein and then drying the heat treated, pH-adjusted solution including the precipitated soy protein or optionally heat treating the pH-adjusted solution including the precipitated soy protein then recovering and drying the precipitated soy protein.

7. The method of claim 6 wherein said heat treatment is effected at a temperature of about 70 to about 160 C. for about 2 seconds to about 60 minutes.

8. The method of claim 7 wherein said heat treatment is effected at a temperature of about 80 to about 120 C. for about 15 seconds to about 15 minutes.

9. The method of claim 8 wherein said heat treatment is effected at a temperature of about 85 to about 95 C. for about 1 to about 5 minutes.

Description

EXAMPLES

(1) In the Examples which follow, all freeze dried products were ground to a powder, the protein content of the powders was determined by a combustion method using a Leco Nitrogen Determinator and the moisture content of the powders was determined by an oven drying method. Spray dried products were analyzed similarly but did not require grinding prior to analysis.

(2) Sensory evaluation of samples was performed as follows.

(3) Samples were presented for sensory evaluation as a 2% protein w/v dispersion in purified drinking water at about pH 6. An informal panel of 6 to 8 panelists was asked to blindly compare the experimental sample to a sample of S013-K19-09A conventional JEP pH 6 product, prepared as described in Example 1 below, and to indicate which sample had the more beany flavour.

Example 1

(4) This Example illustrates the preparation of a soy protein isolate by conventional isoelectric precipitation.

(5) 30 kg of soy white flake was added to 300 L of RO water at ambient temperature and the pH adjusted to 8.5 by the addition of 1M sodium hydroxide solution. The sample was agitated for 30 minutes to provide an aqueous protein solution. The pH of the extraction was monitored and maintained at 8.5 throughout the 30 minutes. The residual soy white flake was removed and the resulting protein solution clarified by centrifugation and filtration to produce 278.7 L of filtered protein solution having a protein content of 2.93% by weight. The pH of the protein solution was adjusted to 4.5 by the addition of HCl that had been diluted with an equal volume of water and a precipitate formed. The precipitate was collected by centrifugation then washed by re-suspending 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 with a protein content of 18.15 wt %. This represented a yield of 72.0% of the protein in the clarified extract solution. An aliquot of 16.64 kg of the washed precipitate was combined with an equal weight of RO water and then the pH of the sample adjusted to 6 with sodium hydroxide. The pH adjusted sample was then spray dried to yield an isolate with a protein content of 93.80% (N6.25) d.b. The product was designated S013-K19-09A conventional IEP pH 6.

Example 2

(6) This Example illustrates one procedure for the preparation of a pH adjusted soy protein isolate.

(7) 30 kg of defatted, minimally heat processed soy flour was added to 300 L of 0.15 M CaCl.sub.2 solution at ambient temperature and agitated for 3.0 minutes to provide an aqueous protein solution. An additional 300 L of 0.075 M CaCl.sub.2 solution was added and the residual soy flour was removed and the resulting protein solution was clarified by centrifugation to produce 532.5 L of centrifuged protein solution having a protein content of 1.22% by weight. The pH of the sample was then lowered to 3.09 with diluted HCl.

(8) The diluted and acidified protein extract solution was reduced in volume from 532 L to 107 L by concentration on a polyethersulfone (PES) membrane having a molecular weight cutoff of 100,000 Daltons. The concentration step and subsequent membrane processing steps were all conducted at approximately 30 C. The solution was diafiltered with 370 L of reverse osmosis (RO) purified water followed by further concentration to provide 37.86 kg of concentrated protein solution with a protein content of 13.97% by weight. This represented a yield of 81.4 wt % of the initial clarified protein solution.

(9) A 1.5 kg sample of the concentrated protein solution was treated with a 25% w/v aqueous sodium hydroxide solution to raise the pH of the sample to 6 and form a precipitate. The precipitate was collected by centrifugation at 10,000 g and then freeze dried to form a product called S009-D27-09A S701N having a protein content of 106.53 wt % (N6.25) on a dry weight basis.

(10) All of the sensory panelists (6 of 6) evaluating the S009-D27-09A 5701N rated this sample as less beany than the conventional IEP control, prepared as described in Example 1.

Example 3

(11) This Example illustrates another procedure for the preparation of a pH adjusted soy protein isolate.

(12) 60 kg of defatted, minimally heat processed soy flour was, added to 600 L of 0.15 M CaCl.sub.2 solution at ambient temperature and agitated for 30 minutes to provide an aqueous protein solution. An additional 600 L of 0.075 M CaCl.sub.2 solution was added and the residual soy flour was removed and the resulting protein solution was clarified by centrifugation and filtration to provide 975 L of filtered protein solution having a protein content of 1.15% by weight. A half volume of water was added and the pH of the sample lowered to 3.05 with diluted HCl.

(13) The diluted and acidified protein extract solution was reduced in volume from 1505 L to 305 L by concentration on a polyethersulfone (PES) membrane having a molecular weight cutoff of 100,000 Daltons. The concentration step and subsequent membrane processing steps were all conducted at approximately 30 C. The solution was then diafiltered with 650 L of reverse osmosis (RO) purified water followed by further concentration to provide 59.44 kg of concentrated protein solution with a protein content of 15.51% by weight. This represented a yield of 82.2 wt % of the initial filtered protein solution.

(14) A 10.20 kg sample of concentrated protein solution was diluted with an equal volume of water to aid mixing during the subsequent heating step.

(15) The diluted solution was adjusted to pH 6 with a 25% w/v aqueous solution of sodium hydroxide and then heated to 95 C. for 5 minutes while mixing in a jacketed steam kettle. Heavy precipitation occurred on adjusting to pH 6.

(16) The heated solution then was cooled and centrifuged at 4,000 g to separate the precipitated material from the soluble fraction. The resulting pellet was re-suspended in reverse osmosis (RO) purified water for spray drying. The dry product was designated S008-E11-09A S701NH and had a protein content of 101.02 wt % (N6.25) on a dry weight basis.

(17) The majority of the sensory panelists (5 of 8) evaluating the 5008-E11-09A 8701NH rated this sample as less beany than the conventional IEP control, prepared as described in Example 1.

Example 4

(18) This Example illustrates another procedure for the preparation of a pH adjusted soy protein isolate.

(19) 30 kg of defatted, minimally heat processed soy flour was added to 300 L of 0.15 M CaCl.sub.2 solution at ambient temperature and agitated for 30 minutes to provide an aqueous protein solution. An additional 300 L of 0.075 M CaCl.sub.2 solution was added and the residual soy flour was removed and the resulting protein solution was clarified by centrifugation and filtration to produce 525 L of filtered protein solution having a protein content of 1.32% by weight. A half volume of water was added and the pH of the sample lowered to 3.08 with diluted HCl. The diluted and acidified protein solution was then heated at 90 C. for 1 minute then cooled to 50 C. for membrane processing.

(20) The diluted, acidified and heat treated protein extract solution was reduced in volume from 781.5 L to 156.5 L by concentration on a polyethersulfone (PES) membrane having a molecular weight cutoff of 100,000 Daltons. The concentration step and all subsequent membrane processing steps were conducted at approximately 50 C. The solution was then diafiltered with 150 L of reverse osmosis (RO) purified water followed by further concentration to a volume of 43.5 L. The solution was then diafiltered with an additional 150 L of reverse osmosis (RO) purified water, then further concentrated to 19.5 L. RO water was then added to the sample to give a total mass of 72.74 kg of diluted protein solution having a protein concentration of 9.47 wt %. This represented a yield of 99.4% of the initial filtered protein solution.

(21) A 30 kg sample of the diluted protein solution was adjusted to pH 6 with a 25/s w/v aqueous sodium hydroxide solution and heated to 90 C. for 5 minutes while mixing in a jacketed steam kettle. Heavy precipitation of protein occurred on adjusting to pH 6.

(22) The heated solution was cooled and the precipitate allowed to settle out. The soluble fraction was decanted off and replaced by an equal volume of water to re-suspend the solids. The slurry was allowed to settle and the liquid phase then was decanted again to remove the remaining traces of the soluble fraction.

(23) The resulting precipitate was then spray dried. The dried product was designated S010-E26-09A S701NH and had a protein content of 101.46 wt % (N6.25) on a dry weight basis.

(24) All of the sensory panelists (6 of 6) evaluating the S010-E26-09A S701NH rated this sample as less beany than the conventional IEP control, prepared as described in Example 1.

Example 5

(25) This Example illustrates another procedure for the preparation of a pH adjusted soy protein isolate.

(26) 30 kg of defatted, soy white flakes were added to 300 L of 0.13 M CaCl.sub.2 solution at 60 C. and agitated for 30 minutes to provide an aqueous protein solution. The residual soy white flakes were removed and the resulting protein solution was clarified by centrifugation to produce 252.4 L of centrifuged protein solution having a protein content of 2.72% by weight. The clarified protein solution was then added to 188.7 L of reverse osmosis (RO) purified water at 60 C. and the pH of the sample lowered to 3.38 with dilute HCl.

(27) 420 L of the diluted and acidified protein extract solution was reduced in volume to 100 L by concentration on a polyethersulfone (PES) membrane, having a molecular weight cutoff of 100,000 Daltons, operated at a temperature of approximately 55 C. At this point, the acidified protein solution, with a protein content 4.82 wt %, was diafiltered with 150 L of reverse osmosis purified water, with the diafiltration operation conducted at approximately 56 C. The diafiltered solution was then concentrated to a volume of 52 L and diafiltered with an additional 468 L of RO water, with the diafiltration operation conducted at approximately 60 C. After this second diafiltration, the protein solution was concentrated from a protein content of 9.99% by weight to a protein content of 13.12% by weight and then diluted to a protein content of 6.44% by weight with water to facilitate spray drying or further processing. The diluted protein solution before spray drying or further processing was recovered in a yield of 74.7 wt % of the initial clarified protein solution.

(28) A 1.8 kg sample of the diluted protein solution was treated with 6 M aqueous sodium hydroxide solution to raise the pH of the sample to 6.08 and form a precipitate. The sample was then freeze dried to yield a product called S023-L09-10A S701N (no fractionation). This product had a protein content of 103.47 wt % (N6.25) d.b.

(29) Another 1.8 kg sample of the diluted protein solution was further diluted with 1.8 L of RO purified water and then was treated with 6 M aqueous sodium hydroxide solution to raise the pH of the sample to 6.00 and form a precipitate. The pH 6 solution was heated to 95 C. for 5 minutes and then freeze dried. The dry product was called S023-L09-10A S701NH (no fractionation) and had a protein content of 103.14 wt % (N6.25) d.b.

Example 6

(30) This Example contains an evaluation of the solubility in water of the soy protein isolates produced by the methods of Examples 2 to 5. Protein solubility was evaluated using a modified version of the procedure of Morr et al., J. Food Sci. 50:1715-1718.

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

(32) The natural pH values of the protein isolates produced in Examples 2 to 5 are shown in the following Table 1:

(33) TABLE-US-00001 TABLE 1 Natural pH of dispersions prepared in water at 1% protein w/v batch product Natural pH S009-D27-09A S701N 5.31 S008-E11-09A S701NH 5.86 S010-E26-09A S701NH 6.10 S023-L09-10A S701N (no fractionation) 5.81 S023-L09-10A S701NH (no fractionation) 5.71

(34) The solubility results are set forth in the following Table 2.

(35) TABLE-US-00002 TABLE 2 Solubility of products at different pH values Solubility (%) Batch Product pH 2 pH 3 pH 4 pH 5 pH 6 pH 7 Nat. pH S009-D27-09A S701N 89.1 100 41.4 5.4 31.3 77.1 5.1 S008-E11-09A S701NH 13.8 5.5 4.0 0.0 11.7 9.0 4.1 S010-E26-09A S701NH 6.6 0.0 0.0 0.0 0.0 0.0 0.0 S023-L09-10A S701N 97.7 100 8.3 0.0 4.8 8.9 0.0 (no fractionation) S023-L09-10A S701NH 0.0 0.0 0.0 0.0 0.0 0.0 0.0 (no fractionation)

(36) As may be seen from the results in Table 2, the S701N products were quite soluble at pH 2 and 3, but not as soluble at the other pH values tested. Addition of a heat treatment to form S701NH resulted in a product that was almost completely insoluble at all the pH values tested.

Example 7

(37) This Example contains an evaluation of the water binding capacity of the soy protein isolates produced by the methods of Examples 2 to 5

(38) Protein powder (1 g) was weighed into centrifuge tubes (50 ml) of known weight. To this powder was added approximately 20 ml of reverse osmosis purified (RO) water at the natural pH. The contents of the tubes were mixed using a vortex mixer at moderate speed for 1 minute. The samples were incubated at room temperature for 5 minutes then mixed with the vortex mixer for 30 seconds. This was followed by incubation at room temperature for another 5 minutes followed by another 30 seconds of vortex mixing. The samples were then centrifuged at 1,000 g for 15 minutes at 20 C. After centrifugation, the supernatant was carefully poured off, ensuring that all solid material remained in the tube. The centrifuge tube was then re-weighed and the weight of water saturated sample was determined.

(39) Water binding capacity (WBC) was calculated as:
WBC (ml/g)=(mass of water saturated samplemass of initial sample)/(mass of initial sampletotal solids content of sample)

(40) The water binding capacity results obtained are set forth in the following Table 3

(41) TABLE-US-00003 TABLE 3 Water binding capacity of various products batch product WBC (ml/g) S009-D27-09A S701N 2.40 S008-E11-09A S701NH 3.71 S010-E26-09A S701NH 3.60 S023-L09-10A S701N (no fractionation) 2.90 S023-L09-10A S701NH (no fractionation) 5.96

(42) As may be seen from the results of Table 3, inclusion of a heat treatment in the preparation of the pH adjusted product resulted in a higher water binding capacity.

SUMMARY OF DISCLOSURE

(43) In summary of this disclosure, the present invention provides procedures for producing soy protein isolates with near neutral natural pH values which can substitute for conventional soy protein isolates in a variety of food applications. Modifications are possible within the scope of the invention.