GB2132206A - Improved process for the production of protein fibres - Google Patents

Abstract

Smooth, elastic and even protein fibres are formed by extruding a mixture of protein micellar mass (PMM) and gellable starch into hot water. The starch may be present in an amount up to about 30 wt% of the PMM. A wide variety of properties can be achieved by varying the concentration of starch. An increase in fibre strength and elasticity is achieved at low concentrations of starch while softer fibres of increased moisture content result at higher concentrations of starch. The fibres are useful in a variety of food analog products.

Description

SPECIFICATION Improved process for the production of protein fibres The present invention is concerned with the production protein fibres.

In U.S. Patent No.4,328,252, assigned to the assignee herein, the disclosure ofwhich is incorporated herein by reference, there is described a process forthe formation of protein fibres in which a protein isolate, known as protein micellar mass, sometimes referred to herein as "PMM", is injected into hot water having a temperatu re above 90 C th roug h plurality of openings.

The novel protein isolate is defined in U.S Patent No.4,285,862, assigned to the assignee of this application, disclosure ofwhich is incorporated herein by reference, as a substantially u ndenatured protein isolate product containing at least about 90% by weight of protein (as determined by Kjeldahl nitrogen x 6.25) and intheform of an amorphous protein mass which isformed by settling the solid phase from an aqueous dispersion of protein micelles consisting of homogeneous amphiphilic protein moietiesandformedfrom at leastone protein source material, the product having substantially no lipid content, substantially no lysinoalanine content and substantially the same lysine content as the storage protein in the source material.

Such novel protein isolate may be formed by the procedure defined in U.S. Patents Nos. 4,169,090, 4,208,323,4,296,026 and 4,307,014, assigned to the assignee herein, the disclosures of which are incorporated herein by reference. In these patents, there are described procedures for isolating protein from protein source materials by solubilizing the protein by contact of the protein source material with sodium chloride solution undercritical pH and ionic strength conditions and diluting the protein solution with water to a lower ionic strength to cause the formation of the dispersion of protein micelles in the aqueous phase from which is settledastheamorphous protein micellar mass.The protein solution may be subjected to ultrafiltration priortethe dilution step and the settling may be:enhanced by centrifugation.

The process of U.S. Patent No.4,169,090 involves solubilizing the protein in the vegetable protein source material ata temperature of about 1 into 35"C using a food grade salt solution having a concentration of at least 0.2 molar ionic strength and a pH of 5.5 to 6.3 to form a protein solution, and diluting the protein solution to an ionic strength of less than 0.1 molarto causeformation ofthe dispersion.

The process of U.S. Patent No.4,208,323 involves solublizing the protein in the vegetable protein source mateFtaIat a temperature of about 1 50to about 3500 using a food grade salt solution having a concentration of at least 0.2 molar ionic strength and a pH of about 5to about 6.8 to form a protein solution, increasing the protein concentration ofthe protein solutionwhile maintaining the ionic strength thereof substantially constant, and diluting the concentrated protein solution to an ionic strength below about 0.2 molarto cause formation ofthe dispersion.

In the latter process, the food grade salt solution prefereably has an ionic strength of about 0.2 to about 0.8 molar and a pH of about 5.3 to about 6.2. In addition, the protein concentration step is preferably effected by a membrane technique at a volume reduction factor about 1.1 to about 6.0, as determined by the ratio of volume of protein solution and the volume of concentrated protein solution.

Further, the dilution of the concentrated protein solution is preferably effected by passing the concentrated protein solution into a body of water having a temperature below about and a volume sufficient to decrease the ionic strength of the concentrated protein solution to a value of about 0.06 to about 0.12 molar.

In one embodiment of the latter process, the food grade salt solution has a pH of about 5to about 5.5 and the phosphrous contentofthe protein solution is decreased priortothe dilution step.

The food grade salt used in the above-described solubilization procedures usually is sodium chloride, although othersalts,such as, potassium chloride or calcium chloride may be used.

As is setforth in U.S. Patent 4,296,026, the purity of isolate which is obtained from soybeans may be improved bythe presence of millimolar amounts of calcium chloride in the aqueous sodium chloride solution. As described therein, the protein is solubilized by contactwith an aqueous sodium chloride solution having an ionic strength of at least about 0.2 molar and containing about 0.001 to about 0.01 M calcium chloride and having a temperature of about 15 to about 75"C.

Further, as is set forth in U.S. Patent No.4,307,014, the yield of isolate which is obtained from soybeans may be improved by effecting the protein solubilization at a temperature of about 150 to about 7500 using an aqueous food grade salt solution of ionic strength of at least 0.2 M and a pH of about 5.6to about7.0, preferably about 6.0 to about 6.4, and then adjusting the pH ofthe protein solution to a pH of about 4.8to about 5.4, preferably about 5.1 to about 5.3, prior to dilution ofthe pH-adjusted protein solution.

While the procedure ofthe aforementioned U.S.

Patent No.4,238,252 produces protein fibres, the quality of the fibres obtained is sensitive to pH of the PMM and optimum fibre strength and elasticity are obtained only over a narrow range of about 5.6 to 5.7.

Further, the range of fibre strength and elasticity, and hence texture variations which can be obtained, is quite narrow.

It has now been surprisinglyfound that smooth, uniform and elastisfibres having awide variety of textural characteristics maybeformed upon extrusion of protein micellar massthrough openings into a hot water bath, by the incorporation of a gellable starch into the protein micellar mass prior to injection of the mixture into hotwater.

The presence of the starch in admixture with the protein micellar mass also improves significantly the flow properties ofthe PMM and enables significant control overthe process to be exercised and the smooth, uniform and elastic fibres to be obtained in consistent manner. The pH of PMM over while good qualityfibresmay be formed is also considerably broadened by the presence of the starch in admixture with the PMM.

The concentration of starch present in the PMM affectsthe quality of fibres which are obtained.

Generally, underthe same extrusion conditions, lower concentrations of starch tend to produce higher strength elastic fibres having good chewiness, suitable for use in meat analogs, while higher concentra tions of starch tend to produce softer, juicierfibres which are useful in seafood analogs.

It has been found that small quantities of gellable starch in the range of about 0.5 to about 5 wt% of the PMM, preferably about 1 to about 2.5 wt.% ofthe PMM, only are required to improve the flow properties ofthe PMM and to obtain smooth, even and elastic fibres of improved fibre strength. Higher levels of starch up to about 30 wt% may be used to achieve modification ofthetexture ofthefibres produced, with greater concentrations leading to softer fibres of higher water content. The properties ofthe fibres produced, therefore, may be varied over a wide range by manipulation ofthe starch concentration.

This variation in properties enables the protein fibres to be used in a variety of meat and seafood analogs. The fibres impart texture and chewiness to the product and may be provided in a form which is very similarto the natural protein fibres present in the productforwhich the analog is being provided.

The fibres of the invention may be used in simulated adiposetissue, bacon analogs, meat snack analogs, sausage meat and other meat analogs, shrimp and crab meat analogs, soup mixes, stews and casseroles.

The starch which is used in this invention may be any gellable starch material. Cornstarch is preferred, in view of its ready availability, although starches from other materials, for example, tapioca and peas, may be used, if desired.

The protein source from which the PMM is formed is usually a plant protein, including cereals, for example, wheat, corn, oats, rye, barley and triticales, legumes, for example, field peas, chickpeas, fababeans, navy beans and pinto beans, and oil seeds, such as soybeans.

The PMM is made from the source material bythe procedures setforth in U.S. Patents Nos. 4,169,090, 4,208,323,4,296,026 and 4,307,014 referred to above.

It is sometimes beneficial to solubilizethe protein material ata higher pH, adjustthe pH ofthe resulting protein solution to a lowervalue and then precipitate the PMM atthe lower pH, so as to take advantage of the higher overall yield attainable atthe higher pH of solubilization and the greater moisture content of the PMM material that results atthe lower pH of precipitation. Such higher moisture level facilities incorporation of the starch into the PMM.AdjustmentofpH in the solution process is described in the aforementioned U.S. Patent No. 4,307,014.

The fibres are formed in this invention by extruding the mixtures of PMM and starch through a plurality of openings or a single opening into a bath of a coagulating medium, usually water. In order to achieve fibre formation, the extruded material must be exposed to heat for a sufficient time and at a sufficienttemperature effectively to denature the extruded protein in the form of fibre monofilaments which maintain their integrity when removed fromthe bath.

In orderto ensure that the extruded material maintains its structural integrity for a sufficient period to ensure that heat setting occurs, a bath temperature of at least about 90"C usually is used, preferably, for a water bath, the temperature is at least about 95"C, since rapid penetration of heat into thefibre and rapid denaturation of the protein into distinct fibre monofilaments occurs. The water bath may have a pH of about5.5to 7.5.

The presence of starch in the admixture with PMM causes an increase in viscosity of the PMM as well as a decrease in the overall moisture content Above about 5wt% starch, heating ofthe admixture, however, results in a significant decrease in the viscosity ofthe admixture. It is preferred, at these concentrations of starch, to preheatthe admixtureto a temperature of about 400 to about 6000 priorto extrusion ofthe preheated mixture to the coagulating bath. Such preheating ofthe PMM-starch mixture may be achieved in any convenient manner, for example, by immersion ofthe extrusion nozzle in the hotwater bath.

Fibres which are produced in accordance with U.S.

Patent No.4,328,252 exhibit a variation in strength depending on pH ofthe PMM which is extruded into the hot water, peaking at around pH 5.6 to 5.7. While fibres are produced from PMM overthe pH range of 5.55 to 5.85 in the prior procedure, fibres produced from PMM having a pH atthe lower end of this range tend to be lumpy and lack strength. The presence of starch in admixture with the PMM results in an approximately uniform strength offibres overthe entire pH range and alsotheformation of fibres of smooth and uniform appearance.

The diameter of the fibres obtained bythe process oftheinvention maybevariedbyvaryingthediameter ofthe openingsthrough which the PMM and starch mixture is injected into the hot water. Usually, the diameter ofthe openings is in the range of about 0.005 to about 0.020 inches.

Coloured fibres may be produced by mixing colouring agents in with the PMM and starch admixture prior to extrusion ofthefibres. Using isoelectricfibre formation processes, involving extraction of protein at high pH and then extruding into an acid bath, itis usually not possibleto colourthe fibres in this way, sincefoodcolouring agentstendto be pH sensitive materials.

The fibres may be dried without loss of structural integrity, and may be transported or stored in this form. The dehydratedform ofthefibres may be used in dry soup mixes orthe like. The fibres are readily rehydrated to their initial form without loss of their beneficial properties. Further, the fibres may be frozen wet and thawed without loss of structural integrity EXAMPLES Example 1 This Example illustratestheformation of protein fibres in accordance with this invention Soy PMM formed following the procedure of U.S. Patent No.4,208,323 Soybean concentrate (about 50 wt% protein) was mixed with 50 Imperial gallons of0.35molarsodium chloride solution ata 15% wIv concentration at a temperature of about 2500.

The mixture was stirred for about 30 minutes at a pH of about 5.8. The aqueous protein extract was separated from residual solid matter.

The extract was concentrated on an ultrafiltration unit using a "ROMICON" (Trademark) type XM50 and a Romicon type PM50 cartridge for a time sufficient to achieve a volume reduction factoroffourtimes. The Romicon ultrafiltration cartridges are manufactured by Rohm and Haas Company, the designation "50" referring to a molecular weight cut-off of 50,000 Daltons.

The concentrate was diluted into cold water having a temperature of 700 to an ionic strength of 0.1 molar whereupon a white cloud of protein isolate formed in the dilution system. The protein dispersion was allowed to settle as a highly viscous amorphous gelatinous precipitate (wet PMM) in the bottom of the dilution vessel. The wet PMM was separated from the residual aqueous phase.

198g of wet PMM were mixed with 2g of cornstarch and the pH adjusted to 5.6. The starch-PM M mixture was centrifuged at 5000 x g for 5 minutes at 2000 to remove excess water and entrapped air.

The mixturewas loaded into a fibre-forming apparatus comprising an elongate tube having a plurality of orifices of diameter 0.020 inches at the lower end and an air pressure inlet at the upper end.

The orifices were immersed in a hot water bath having a temperature of about 95"C and the mixture was extruded through the orifices downwardly into the hot water bath using 12 psi air pressure. The fibres were extruded forthree minutes and allowed to heat set for a furthertwo minutes before removal from the hot water bath. The fibres were smooth, elastic and even, compared with lumpy, twisted and inelastic fibres produced from the PMM without added starch.

Testing of the strength ofthe fibres was effected in a gel matrix. The basic gel was formed from a 20% w/w dispersion of soy PMM at pH 5.5 and 0.3 M NaCI.

Fibres were cut to 1/4-inch lengths and incorporated into the dispersion to a concentration of 49 of fibres to 30 ml of dispersion. The mixture of protein isolate dispersion and fibre pieces was heat set in a greased stainless steel gel tube of dimensions 21/2 in. x 3/4 in.

I.D. at 100"for45 minutes and then cooled to 2000for 20 minutes.

The shear strength of the gels was measured using the Warner-Bratzler apparatus, which is described in detail in an article entitled "Modification Of Texture Instruments" by P. W. Voisey, J. of Texture Studies, 2 (1971),p.129to 195.

Example 2 This example illustrates the effect of starch on fibre strength and fibre moisture content.

(a) The procedure of Example 1 was repeated for theformation ofproteinfibresandforthedetermina- tion ofshearstrength. The initial protein extraction was effected at 0.3 M NaCI and pH 5.55 and the PMM had a pH of 5.55 prior to extrusion. Varying quantities of starch were incorporated into the PMM and the fibre moisture content was determined in each case.

The results obtained are reproduced in the following Table I below: TABLE I Sample Shear Force Fibre Moisture (kg) (wt%) Base Gel 1.9 PMM + O wt% starch 2.8 66.7 + 1 wt% 4.7 66.2 + 5 wt% 2.8 72.1 + 10 wt% 2.3 78.3 + 15 wt% 1.9 + 20 wt% 1.8 83.8 The results ofthe above Table I showthat a small quantity of starch significantly increases the fibre strength and perceived toughness but the strength drops offatgreater concentrations of starch, until in the 15 to 20 wt% range the fibres do not increase the strength of the base gel.

As can also be seen from the results of Table I, the moisture content and perceived juiciness of the fibres increases with increasing starch concentration. The fibres produced at 15 to 20 wt% starch are quite soft and, though of low strength, are suitable for seafood analog use where soft fibres are desirable and strength is less of a factor.

(b) The effect of starch on fibre moisture was again tested following the procedure of Example 2(a), except that in this case the pH of the PMM extruded was 5.65. The moisture content of the PMM and the starch mixture priorto extrusion also was determined. The results obtained are reproduced in the following Table ll; TABLE II PMM Fibre Starch Moisture Moisture (wt%) {%) (%) 0 56 64 5 62 73 10 58 72 15 56 80 20 55 - 25 54 85 It will be seen from the results of Table II that increasing the amount of starch in the PMM and starch mixture decreases the overall moisture content of the mixture while the moisture content of the fibres produced from such mixtures increases significantly.

(c) The effect of low concentrations of starch and pH of PMM on the strength of fibres produced was tested by producing fibres under variable conditions following the procedure of Example 2(a). The results obtained are reproduced in the following Table Ill: TABLE Ill Starch Shear Strength (kg) (wt%) pH5.55 5.65 0 3.8 3.3 0.5 3.8 3.4 1.0 3.7 3.6 1.5 4.2 3.9 2.0 3.6 5.4 2.5 3.6 4.2 3.0 3.5 3.7 4.0 3.6 3.1 Base Gel 2.3 1.9 The results ofthe above Table Ill demonstrate that the quantity ofstarch required to achieve a maximum of strength varies with pH. The apparent discrepancy between the results shown in Table Ill with those setforth in Table I is explained by variation in properties based on differences within batches of PMM.However, itwill be seen from the data presented in Tables I and Ill that the incorporation of about 1 to 2.5 wt% of starch achieves an increase in fibre strength.

These experimental determinations were confirmed by subjective organoleptic evaluation.

Example 3 This Example illustrates to use of different starchs in fibre formation.

The effect of starch from various sources on fibre formation was tested. Fibres were produced from soy PMM of pH 5.65 containing 5 wt% starch following generallythe procedure of Example 1.

As may be seen from the results reproduced below in n Table IV, when a gellable starch was used, good flow characteristics were observed with the formation of smooth, elastic and uniform fibres, whereas the absence of fibre formation was observed when a pregelatinized starch material was used.

The results are reproduced in the following Table IV: TABLE IV Starch Observations Tapioca good flow Pea good flow Corn good flow Pregelatinized Maize no fibre formation Example 4 This Example illustrates the effect of pH of PMM on fibre strength.

Fibres were formed from soy PMM following generally the procedure of Example 1 with variation ofthe pH of the PMM samples extruded into the hot water bath. In the absence of added starch, at lower pH values, the lower moisture content ofthe PMM led to uneven flow and the production of fibres that were lumpy and lacking in strength.

With the addition of cornstarch, flow was improved and elastic, smooth and even fibres were obtained.

The shear strength ofthefibres was determined in each case and the results are reproduced in the following Table V: TABLE V pH Shear Strength (kg) Starch Concentration (%) 0 5 10 5.4 1.2 2.7 2.4 5.5 - 2.9 2.6 5.55 - 3.0 2.4 5.6 2.2 2.6 2.2 5.7 - - 1.9 As may be seen from the results of Table V, in the absence of added starch, the maximum fibre strength was at pH 5.6 and strength decreases occur witch decreasing pH,whereasadditionsofstarch produced fibres of similar strength throughoutthe pH range.

Example 5 This Example illustreates the effect of temperature and starch on the viscosity of PMM.

Soy PMM produced bythe procedure of Example I at pH 6.0 was tested for viscosity using a Haake Rotovisco RV 100 rotational viscometer at a shear rate of 98 sec-1 at various concentrations of added starch and at various temperatures.

The results obtained are reproduced in thefoltow- ing Table VI: TABLE Vl Sample Viscosity (Pa. sec) wt% Starch 30"C 40"C 50"C 0 1.22 - 2.70 1 2.09 3.48 4.53 5 9.40 6.62 5.05 10 14.88 9.14 4.09 20 15.41 9.14 5.05 As may be seen from the results of Table VI, the addition of starch increased the viscosity at 30"C.

While atO and 1% starch, increasingthetemperature increased the viscosity of the PMM, at higher starch concentrations, however, the viscosity decreased rapidly with temperature.

Example 6 This Example illustrates the utilization of PMM from other protein sources in the production of protein fibres.

Fababean PMM and pea PMM,formed using the procedure of Example 1 with 0.35 M sodium chloride and pH 5.8 in the extraction ofthe protein, were used to form fibres in the presence and absence of added starch bythefibre-forming operation of Example 1.

In each case, the presence of the starch resulted in anevenflowofthe PMM-starch mixture into the hot water bath and the formation of smooth, elastic and even fibres.

In summaryofthis disclosure, the present invention provides an improved procedureofformation of protein fibres of a wide range of properties by the addition of starch to protein micellar mass prior to extrusion ofthefibresfromthe mixture into a coagulating medium. Modifications are possible within the scope ofthis invention.

Claims (21)

1. A process for the production of protein fibres, which comprises: admixing gellable starch with a substantially undenatured vegetale protein isolate formed by settling an aqueous dispersion of protein micelles consisting of homogeneous amphiphilic protein moieties to form an admixture containing up to about 30 percent by weight of starch, and injecting said admixture through at least one opening into a hot coagulating medium having a sufficient temperature to effect denaturation ofthe protein isolate and maintain structural integrity ofthe extruded material.

2. A process according to claim 1 wherein said coagulating medium has a temperature of at least 90"C.

3. A process according to claim 2 wherein said coagulating medium has a temperature of at least about 95 C.

4. A process according to any one ofclaims 1 to 3 wherein said coagulating medium is water.

5. A process according to claim 4 wherein said water has a pH of about 55to about 7.5.

6. A process according to any one of claims 1 to 5 wherein there is a plurality of openings having a diameter of 0.005 to 0.020 inches.

7. A process according to any one of claims 1 to 6 wherein the concentration of starch is 0.5 to 5 wt% of the protein isolate.

8. A process according to claim 7 wherein the concentration of starch is about 1 to about 2.5 wt%.

9. A process according to any one of claims 1 to 6 wherein the concentration of starch is 5 to 30 wt% of protein isolate and said admixture is preheated to a temperature of about 40 C to about 60 C prior to injection into said water.

10. A process according to any one of claims 1 to 9 wherein said isoiate has a pH of 5.55 to 5.85.

11. A process according to any one of claims 1 to 10 wherein said starch iscornstarch.

12. A process according to any one of Claims 1 to 11 in which the protein isolate is prepared by settling an aqueous dispersion of protein micelles consisting ofamphiphilic protein moieties and formed from at least one vegetable protein source material to provide an amorphous protein mass containing a substantiallyundenatured protein isolate, said isolate having substantially no lipid content, substantially no lysinoalanine content and substantially the same lysine content as the storage protein in the protein source material and separating the amorphous protein mass from residual aqueous phase.

13. A process according to claim 12 wherein said aqueous dispersion of protein micelles from which said isolate is settled is formed by solubilizing the protein in said at least one vegetable protein source material using a food grade saltsolution having a concentration of at least 0.2 molar ionic strength and a pH of 5.5 two 6.3 to form a protein solution, and diluting the protein solution to an ionic strength of lessthan 0.1 molartocauseformation of said dispersion.

14. A process according to claim 12 wherein said aqueous dispersion of protein micellesfrom which said isolate is settled is formed by solubilizing the protein in said at least one vegetable protein source material using afood grade salt solution having a concentration of at least 0.2 molar ionic strength and a pH of about 5 to about 6.8 to form a protein solution, increasing the protein concentration of said protein solution while maintaining the ionic strength thereof substantially constant, and diluting the concentrated protein solution to an ionic strength below about 0.2 molar to cause formation of said dispersion.

15. A process according to claim 14 wherein said food grade salt solution has an ionic strength of 0.2 to 0.8 molar, a pH of 5.3 to 6.2, said protein concentration step is effected by a membrane technique at a volume reduction factor of about 1.1 to about 6.0, as determined by the ratio of volume of protein solution and the volume of concentrated protein solution, and the dilution ofthe concentrated protein solution is effected by passing the concentrated protein solution into a body of water having a temperature below about25cCand a volumesufficientto decrease the ionic strength of the concentrated solution to a value of about 0.06 to about 0.12 molar.

16. A process according to claim 15 wherein said protein source material is soybeans, said food grade salt is sodium chloride and said aqueous food grade salt solution contains about 0.001 to about 0.01 M of calcium chloride.

17. A process according to claim 12 wherein said dispersion of protein micellesfrom which said isolate is settled is formed by solubilizing the protein in soybeans at a temperature of about 15 Cto about 750cussing a food grade salt solution having a concentration of at least 0.2 molar ionic strength and a pH of about 5.6 to about 7.0 to form a protein solution, adjusting the pH ofthe protein solution to a pH ofabout4.8 to about 5.4, and diluting the pH-ajusted solution to an ionic strength value sufficiently low to cause formation of said dispersion.

18. A process according to claim 17 wherein said solubilization pH is about 6.0 to about 6.4 and said adjusted pH is about 5.1 to about 5.3.

19. A process forthe production of protein fibres substantially as hereinbefore described with particu larreference to the Examples.

20. Protein fibres when produced by a process as claimed in any one of claims 1 to 19.

21. Novel elastic protein fibres comprising elon- gate monofilaments of a heat coagulated admixture of a substantially undenatured vagetable protein isolate formed by settling an aqueous dispersion of protein micelles consisting of homogenous amphiphilic protein moieties and gellablestarch in an amount up to 30 percent by weight of the mixture.