GB2230932A - Increasing solubility of proteinaceous material - Google Patents

Abstract

The solubility in water, of relatively low water-soluble proteinaceous material of vegetable origin, is increased by a process which comprises subjecting an aqueous slurry of such material in which the weight ratio of water to proteinaceous material solids is between about 3:1 and about 10:1 (preferably below about 6:1), to high forces selected from hydraulic shear and mechanical shear forces, and at a pH within the range of from about 7.0 to about 9.2.

Description

PROCESS FOR INCREASING THE WATER-SOLUBILITY OF LOW WATER-SOLUBLE PROTEINACEOUS MATERIAL FIELD OF THE INVENTION The invention relates to a process for increasing the solubility in water of relatively low water-soluble proteinaceous material of vegetable origin.

BACKGROUND OF THE INVENTION Vegetable protein products obtained from seed and leaf materials are used as replacements and extenders for proteins derived from animal, marine and poultry sources. Such vegetable protein products are usually low fat or defatted materials. They are commonly referred to as "flours" if they contain less than 65% protein, as "concentrates" if they contain from 65 to 90% protein and as isolates" if they contain above 90% protein.

Methods for manufacturing vegetable protein products customarily include heat treatment and aqueous alcohol extraction, as well as other chemical treatments and applied conditions which denature and substantially reduce the solubility cf the protein content of the products. The water solubility of protein in a proteincontaining product is characterized by its Nitrogen Solubility Index (NSI), which is determined by the American Oil Chemists Society Official Method, namely AOCS BA1165 - Official Method.

Since the water solubility of the protein in a vegetable protein product is a desired characteristic in many applications, as for example in food recipes (e.g. in meat, dairy and bakery products) and in more general industrial utilization (e.g. in paper coatings), attempts have been made to increase such solubility, preferably with minimal hydrolysis and otherwise avoiding damage to the native proteins. The techniques hitherto proposed have been generally too expensive or impractical, so far as they relate to the desideratum of producing a low-cost vegetable protein product having increased protein solubility, from a denatured product of low solubility, while avoiding damage to the proteins as aforesaid.

U.S. Patent No. 4,113,716 discloses a process for improving the solubility of denatured defatted soybean flakes, which comprises subjecting an aqueous slurry of the flakes at pH 6.5 to 9.0 to a heat treatment in a jet-cooker at a temperature o in the range of 110 to 140 C for a time of 2 seconds to 3 minutes. This treatment is said to increase the protein solubility of the soybean flakes.

U.S. Patent No. 4,234,620 (Howard et al) discloses a process for improving the solubility of a denatured vegetable protein product having low protein solubility, by subjecting an aqueous feed stream of such product at a temperature between o about 50 to about 150 C and at pH 6.5 to 9.0 to successive pressure and cavitation cycling in a cen- > rifugal homogenizer. An exemplary homogenizer which may be used in this process is that disclosed in U.S. Patent No. 3,744,763.

Howard et al's patent teaches that in general, the water to protein weight ratio in the aqueous feed stream will range from more than 6:1 to about 30:1, advantageously from about 7:1 to about 18:1, a weight ratio of about 9:1 to 15:1 being preferred. It is also stated in this patent that an excessively high solids level (by which term is presumably intended a weight ratio as just mentioned of less than 6:1) "becomes too viscous which can create transfer, uniform homogenization processing, pH control and product recovery problems".The required conditions of successive pressure and cavitation cycling are achieved by a rotor which accelerates the aqueous stream past a stator or stationary rings, typically comprised of a series of projections or depressions such as teeth, holes, pins and the like, operatively arranged at a relatively close tolerance of e.g. 0.25 to 1.3 mm.

As will be appreciated by those skilled in the art, where the protein product of increased solubility needs to be dried, then the Howard et al process will be an expensive one to operate commercially, because the essential employment of relatively large quantities of water will require the employment of a large amount of energy, when the water has to be removed.

The present invention is based on the surprising discovery that the level of water-soluble protein in a vegetable protein product can be increased, without causing substantial protein hydrolysis, by an economical and efficient process, which in contradistinction to the teaching of the Howard et al patent, has low water consumption and low drying energy requirements, and utilizes a viscous slurry as starting material. Moreover, the process of the present invention does not require the use either of centrifugal homogenizer, or of other devices which effect successive pressure and cavitation cycling. As will be seen from the, details described below, the process provided by the invention is relatively simple and provides a low-cost vegetable protein product having improved water solubility, from a corresponding proteinaceous material having low water solubility.

SUMMARY OF THE INVENTION The invention thus provides in one aspect, a process for increasing the solubility in water of relatively low watersoluble proteinaceous material of vegetable origin, which comprises subjecting an aqueous slurry cf said material in which the weight ratio of water to proteinaceous material solids is within the range of from about 3:1 to about 10:1, to high forces selected from hydraulic shear and mechanical shear forces, without the use of successive pressure and cavitation cycling such as is produced in a centrifugal homogenizer, and at a pH within the range of from about 7.0 to about 9.2.

In another aspect, the invention provides a process for increasing the solubility in water of relatively low water soluble proteinaceous material of vegetable origin, which comprises subjecting an aqueous slurry of said material in which the weight ratio of water to proteinaceous material solids is less than about 6:1, to high forces selected from hydraulic shear and mechanical shear forces, and at E pH within the range of from about 7.0 to about 9.2.

Also included within the scope of the invention is a proteinaceous material of vegetable origin which has been prepared by the present process.

DETAILED DESCRIPTION OF THE INVENTION It will be appreciated that in general, the increased solubility achieved by the process of the invention will be measured by an increase in the NSI value. as stated above. The details given in the description which follows apply to both aspects of the invention, as set out above.

T light ratio of water to proteinaceous material solids lies preferably within the range of from about 3: 1 to about 6:1, more preferably within the range of from about 4:1 to about 6:1.

As a source of the required high forces, there may be employed, for example, high speed pulping disintegrating wet milling equipment, which is able to provide high hydraulic and mechanical shear force impacts in a viscous liquid medium. This equipment, in its simplest form, will be a hammer, knife, pin or rotor mill able to disintegrate viscous slurries, for example, those marketed under the trade names "Waring Blender", Stephan Mixer", "Entolator", "Emerson Dualator", and/or similar equipment known per se. An illustrative typical disintegrating ating wet mill of this kind is the "Emerson Dualator" made by Bolton-Emerson" Inc.

of Lawrence, Massachusetts, U.S.A. This wet mill is a vessel which has coaxially mounted contrarotating rotors, one set within the other. Between the contrarotating rotors there is created a high hydraulic shear force which converts the starting material to a fine particulate state which forms in slightly basic medium a true solution and/or a stable colloidal suspension. A jacketed double wall mill vessel enables the injection of steam, and other heating media, or coolants, to be effected.

A preferred pH range for operating the process of the invention is from about 7.3 to about 8.5. While a variety of both organic and inorganic bases may be used to adjust the pH of the initial slurry to the alkaline side of neutrality, as required in accordance with the invention, there is preferably used an alkali metal hydroxide or alkaline earth metal hydroxide, and particularly for human consumption, one of the alkali metal hydroxides NaOH or KOH, or the alkaline earth metal hydroxide Ca(OH) 2 Preferably, the process of the invention is effected at o a temperature within the range of about 60 to about 110 C. The desired temperature may be attained by using warm aqueous basic media, or by injecting steam directly into the slurry, or by utilizing a jacketed double wall construction of the wet mill vessel for indirect heating by steam or other heating media.The heat generated by the disintegration of the protein material in the course of the process of the invention should also be taken into account, and the extent of external adjustment of the temperature should be varied accordingly.

The retention time in the wet mill vessel, when operating the process of the invention, depends both on the degree of granulation and the source of the relatively insoluble proteinaceous starting material. In general, the finer the particle size of the starting material, the shorter the retention time necessary to achieve the object product in accordance with the process of the invention. Also, higher power inputs will generally shorten the retention time. Retention time can thus vary to a great extent, e.g. from one minute or less, to twenty or more minutes, depending on the degree of granulation, the source of the starting material and the power input.

Subsequently to the treatment in accordance with the process of the invention at a pH within the range of from about 7.0 to about 9.2, the pH may be lowered, e.g. to a value within the range of about 6.4 to about 7.0. This adjustment of pH value may be effected, preferably while agitating, either in the same or in a different vessel. For this purpose, although any suitable acid may be used, food grade acids fit for human consumption are evidently necessary where the vegetable protein product is intended for this purpose.

The product of the process, particularly after lowering the pH value as just noted, may be dried to a water content of e.g. not more than about 10%. While any suitable drying method which will not impair the properties of the protein product (and especially the water solubility thereof) may be utilized, it is presently preferred that the product, which is highly viscous, is dried in an air whirl turbine mill able, without denaturing, to simultaneously dry and grind the proteinaceous material. A commercially available air whirl turbine mill of this kind is, for example, "Ultra Rotor" made by Altenburger Maschinen, Jaeckering G.m.b.H., Hamm, West Germany. For the reason stated, methods of drying requiring a prolonged high temperature treatment are generally to be avoided.

The relatively low water-soluble proteinaceous starting material may be, e.g., such material which has been denatured by a method selected from the group consisting of heat treatment, treatment with aqueous alcohol and/or other chemical treatment.

In particular, there may be used for example, defatted vegetable protein products from such non-limiting sources as soybeans, sesame, lupins, cottonseeds, peanuts, rapeseeds, sunflowers, maize, wheat, barley, oats, lentils, legumes generally, vegetable leaves and the like, including "flours", "concentrates" and isolates, as described above.

The invention will be illustrated by the following nonlimitative example.

EXAMPLE Aqueous alcohol extracted soya protein concentrate of low protein solubility [HAYPRO-M, manufactured by Hayes Ashdod Ltd., Ashdod, Israel, having the analysis: nitrogen 10.65% (as is), 11.39% (dry basis); 71.2% protein (dry basis) N x 6.25; 10 NSI; 6.5% moisture; pH 6.8 & 5.5% ash], 5 kg., was combined with 20 1. 0.0375N aqueous NaOH in a pulping disintegrating wet mill "Emerson Dualator" Model 10 vessel tank. The aqueous slurry was subjected to an interfacial rotors speed of 9800 feet per second and a power input of 22 KWH. The temperature was adjusted by passing steam through the vessel tank jacket, producing a final o slurry temperature of 98 C. The initial pH of the mixture was 8.0 and the final pH was 7.7.After a retention time of 10 mins., the slurry was neutralized with 10N HC1, to obtain a final product pH (after drying) of 6.8, agitated for 15 secs. in the same vessel tank and simultaneously dried and ground in an air whirl turbine mill "Ultra Rotor" (model 3a) made by Altenburger Maschinen, Jaeckering G.m.b.H., Hamm, West Germany, to a final moisture content of 6.5%. The dried ground high protein solubility, soya protein concentrate product gave the following analysis: nitrogen 10.04% (as is), 10.74% (dry basis); 67.1% protein (dry basis) N x 6.25; 72 NSI; 6.5% moisture; pH 6.8 & BR< 6.2% ash.

While the invention has been described above with reference to particular embodiments, it will be appreciated by those skilled in the art that many variations and modifications may be made. The invention is accordingly not to be construed as limited to such embodiments, but is defined only by the claims which follow.

Claims (16)

1. A process for increasing the solubility in water of relatively low water-soluble proteinaceous material of vegetable origin, which comprises subjecting an aqueous slurry of said material in which the weight ratio of water to proteinaceous material solids is within the range of from about 3:1 to about 10:1, to high forces selected from hydraulic shear and mechanical shear forces, and at a pH within the range of from about 7.0 to about 9.2.

2. A process for increasing the solubility in water of relatively low water-soluble proteinaceous material of vegetable origin, which comprises subjecting an aqueous slurry of said material in which the weight ratio of water to proteinaceous material solids is less than about 6:1, to high forces selected from hydraulic shear and mechanical shear forces, and at a pH within the range of from about 7.0 to about 9.2.

3. A process according to either claim 1 or claim 2, wherein said ratio is within the range of from about 3: 1 to about 6:1.

4. A process according to claim 3, wherein said ratio is within the range of from about 4:1 to about 6:1.

5. A process according to any of the preceding claims, in which a pulping disintegrating wet mill is utilized as the source of said high forces.

6. A process according to any of claims 1 to 5, in which a disintegrating wet-mill is utilized as the source of said high forces and is selected from hammer, knife, pin and rotor wet mills.

7. A process according to claim 6 in which the wet-mill comprises two sets of contrarotating rotors creating high hydraulic shear forces therebetween.

8. A process according to any of the preceding claims, wherein the pH lies within the range of about 7.3 to about 8.5.

9. A process according to any of the preceding claims, which is effected at a temperature within the range of about 60 o to about 110 C.

10. A process according to any of the preceding claims, wherein subsequent to the treatment at a pH within the range of from about 7.0 to about 9.2, the pH is lowered to a value within the range of about 6.4 to about 7.0.

11. A process according to claim 10, wherein the product is dried to a water content of not more than about 10%.

12. A process according to claim 11, wherein the product is dried in an air whirl turbine mill.

13. A process according to any of the preceding claims, wherein said relatively low water-soluble proteinaceous material is such material which has been denatured by a method selected from the group consisting of heat treatment, treatment with aqueous alcohol and/or other chemical treatment.

14. A process according to any of the preceding claims and substantially as hereinbefore described.

15. A process for increasing the solubility in water of relatively low water-soluble proteinaceous material of vegetable origin, and substantially as hereinbefore described with reference to the Example.

16. A proteinaceous material of vegetable origin which has been prepared by a process according to any of the preceding claims.