NO760655L - - Google Patents

Description

Method for producing a texturized food product.

The invention relates to a method for the production of edible, textured, protein-containing products, which involves bringing a protein solution into contact with a cooling medium, freezing this material in a controlled manner in segregated crystalline layers of solvent separated by intermediate crystalline, cast layers of protein, while all these layers are made to extend in a common, generally normalized direction on the cooled surface,

and to stabilize the structure developed, to obtain a texturized product.

In US Patent 3,870,808 and US Application 124,739, a method is described which comprises the steps of exposing an aqueous slurry, puree or curd of proteinaceous material to a cooling medium, freezing in a controlled manner said aqueous slurrying into ice crystal layers separated by crystalline-cast layers of protein slurry particles, and irreversibly solidifying the crystalline-cast protein layers to form a structured product. The solids content of the slurry is at least 15%, and the protein is present mainly in an undissolved state.

The above-mentioned method has some disadvantages, especially in the case where a meat is used as starting material for the development of structure. Unless the meat contains very little connective tissue or fat, the products obtained show insufficient structure both in the frozen state and after cooking. Cooked products tend to have a dry and crumbly texture.

The applicant has found that the above-identified and other disadvantages associated with the above-mentioned method could be avoided to a large extent if, instead of using a meat puree, one exposes a vegetable protein curd or slurry as described in the state of the art, a protein solution for freezing/texturing .

According to the invention, protein solutions are used

which has its protein present predominantly in a dissolved state.

By "predominantly in a dissolved state" is meant in this description that more than approx. 50% of the protein remains in the supernatant after centrifugation for 60 minutes at 40,000 x G.

Useful solutions of proteins to be subjected to freezing/texturing contain 3-30% protein by weight. The use of proteins originating from different sources can be pushed on. If solutions of myofibrillar proteins, such as meat or fish proteins, are used, concentrations of 3-10%, preferably 6-10%, proteins are suitable and give satisfactory products. If solutions of globular proteins, e.g. proteins isolated from oil-containing seeds are used, concentrations preferably between 10 and 30% are used. The solvent is preferably water or an aqueous salt solution.

The production of solutions of highly functional proteins to be used in the restructuring of a protein-containing food means extraction of the protein from its source and concentration of this soluble extract to a suitable level for the development of structure.

The extraction of protein from its source can be carried out using an aqueous solution of an alkali, under very mild conditions to reduce any denaturation of proteins to a minimum. The alkali solution should be relatively diluted, e.g. with a molarity in the range 0.025 to 0.2m, preferably approx. 0.05 to 0.lm. The temperature of the mixture during the extraction and all the following processing steps should preferably be kept at approx. 20°C or lower. The duration of the extraction should also be kept to a minimum suitable for obtaining a reasonable yield of extracted material. An extraction time in the range of 30-60 minutes is preferred. The alkali used is preferably sodium hydroxide, but other common alkalis, e.g. potassium hydroxide, sodium carbonate, potassium carbonate and ammonium carbonate, can be used if desired.

If an alkali solution is used as the extraction solution, the pH value of the protein solution should be reduced using a diluted, aqueous acid, e.g. hydrochloric acid, sulfuric acid; phosphoric acid or acetic acid. The pH value is preferably adjusted to between 5.0 and 8.5.

Another aqueous solution of a protein solubilizing agent consisting of urea or guahidin hydrochloride or other urea-related compounds, in high concentration can be used. A very useful aqueous extraction solution for meat which is preferably used according to the invention is a release of an alkali metal salt, such as sodium chloride or potassium iodide. such salts can be used in a concentration of up to lm and preferably in a concentration of approx. 0.6m at a pH value between 7 and 9 in the presence of a phosphate buffer.

Concentration of the solution that has been adjusted to the desired pH value can e.g. is carried out using any conventional ultra-filtration apparatus', but a tubular model is preferred. Ultrafiltration causes the removal of unwanted components in the filtrate, e.g. colored materials, saponified fats and salts, and also concentrates the filtrate to provide a solution with increased protein content.

The freezing/texturing of the protein solutions according to the invention is preferably carried out after aerating the protein solution and adjusting the pH value to the desired value (for myofibrillar proteins a pH value between 5.7 and 7.5 is recommended).

Refrigeration temperatures between -30°C and -80°Can usually be used. Regulated freezing/texturing can be carried out in different ways. One of the suitable methods includes unidirectional freezing, which involves freezing in such a way that formation of solvent crystals occurs in one direction. This method is described in detail in the above-mentioned US application, using a partially insulated jacket, one surface of which is brought into contact with a cooling medium. This method will be further illustrated in the examples.

Another method according to the invention consists in subjecting the protein to centrifugal freezing. Centrifugal freezing means an operation whereby the liquid to be frozen is placed in a centrifuge which is then rotated at high speed and at the same time exposed to reduced pressure. This reduced pressure induces solvent evaporation from the surface of the liquid and subsequent directional freezing of most of the liquid.

Stabilization of the structure developed in the frozen protein solutions according to the invention can occasionally be carried out

by direct heat solidification of the frozen protein solution between 80 and 125°C, preferably in a moist atmosphere.

The applicant has found that a particularly advantageous way of stabilizing the developed structure in a frozen solution of protein,

involves freeze drying.

Freeze-drying has proven to be a very suitable method, especially if. proteins are used which, during the heat/solidification treatment of the frozen solutions, would easily redissolve and cause part of the developed structure to disappear.

A method which is preferably used when a solution such as e.g. contains soy proteins, is to be frozen/texturized, includes a centrifugal freezing/drying operation which simultaneously results in the development of structure in the solution and stabilization of the organized structure. The freeze/dried materials are usually further stabilized by heating in a moist atmosphere between 80 and 125°C

Another, very suitable stabilization method involves the addition of a cross-linking agent to the protein solution before freezing/texturing. The cross-linking agent limits protein/water interactions during thawing, which occurs during heat solidification of a frozen protein solution. Introduction of bifunctional bridging reagents limits the free migration of protein molecules. Various types of cross-linking agents are known

the expert in the field, e.g. dialdehyde-alginic acid or dialdehyde starch can be used. Dialdehyde starch is preferably used.

The concentration of the reagents and the pH of the solution require careful control to ensure that most of the ice crystal organization is complete before the cross-linking reaction takes place. The formation of ice crystals themselves provides such a degree of concentration that protein and cross-linking agent are brought into more intimate contact. in the zones where reaction is required. If dialdehyde starch is used, it is recommended to use this reagent in a concentration between 0.5 and 10%, preferably 0.6-1.5%, based on the weight of protein present. The pH of the solution containing dialdehyde starch and protein is adjusted to a pH between 5.7 and 12, preferably between 6 and 9. If further stabilization is required, this can be carried out by heat-denaturation of the frozen solution at a temperature between 80

and 125°C.

The above-described procedure for restructuring.

of proteins offers many advantages associated with the use of protein solutions, as opposed to the use of protein slurries. Among the many advantages can be mentioned:

a) the possibility of an intimate molecular mixture of proteins from different sources so that one obtains advantageous end-product characteristics and the ability to provide a nutritional mixture; b) possibility of extracting functional proteins economically and specifically from e.g. meat or fish scraps; c) making a complicated fine grinding equipment redundant, since the protein solution is already homogeneous; d) easy deaeration of the proteinaceous material before freezing/texturing, which is due to the absence of dense protein particles that prevent the movement of air bubbles; e) easy pumping of protein solutions, which tend to be less viscous than their slurry equivalents; f) greater flexibility and efficiency in the freezing operation due to the lower viscosity of a protein solution; g) achieving better regulation of the structured appearance by varying the protein or salt concentration; h) better organization and full utilization of protein functionality, which is due to the fact that each protein molecule has equal freedom to migrate.

The products obtained by the method according to the invention were tested by subjecting them to texture measurements, which led to the. conclusion that the products produced in accordance with the invention have better structure, or in other words: show a superior anisotropy and are more similar to natural meat, compared to the products from the state of the art. The products according to the invention proved, when subjected to flavoring experiments, to have an elastic and juicy texture when chewed.

Their appearance strongly resembled first-class meat or fish. In what follows, the invention will be illustrated by means of examples.

Example I

5 kg of pre-minced, low-quality beef

was extracted using 50 kg of a solution containing 1750 g of sodium chloride and 240 g of sodium phosphate of pH 7.0.

The temperature during the extraction was between 5 and 10°C. Collagenous material was filtered off, and additional insoluble material was removed by centrifugation. The clear solution was concentrated on a tubular module ultrafiltration system at 20°C. The concentrate contained approx. 3.7% protein, of which approx. 70% was present in a dissolved state. This concentrate was deaerated by centrifugation, and the concentrate's pH value was adjusted to approx. 6.0. The concentrate was poured into cylindrical Perspex molds with vertical walls 7 mm thick, to provide adequate insulation, and was rapidly, controlled, directly frozen on a horizontal bed of solid carbon dioxide at approx. -80°C and then freeze-dried. After completion of the lyophilization step, the samples were transferred to a preheated "Rapidaire" steam oven and held at 100°C to heat solidify the protein. The product was finally rehydrated completely in cold tap water.

Example II

7.5 kg of low quality ground beef was mixed

with 40 kg of tap water using a "Silverson" mixer.

Dense collagen material was then filtered out. 1.75 kg of sodium chloride in 10 kg of tap water was then added, and the pH was adjusted to 12.5 using a 40% sodium hydroxide solution. After 5 minutes, the extract was adjusted to pH 7.0 with 4N hydrochloric acid. Insoluble material was removed by filtration, followed by centrifugation. The clear solution was concentrated by ultra-filtration as described in example-I. A protein concentrate was obtained which had a protein concentration of 5.5%, of which approx. 99% was present in a dissolved state. This concentrate was further processed as described in Example I.

Example III

15 kg of finely chopped cod waste was added to 100 kg

of a 0.5m solution of sodium chloride and mixed during use

of a "Silverson" mixer. The insoluble material was removed

as described in Example I. The clear solution was subjected to ultrafiltration under the same conditions as in Example I.

This concentrate was deaerated by centrifugation and the pH was adjusted to 6.5. The concentrate contained approx. 3.8% protein, of which

more than 50% was present in a dissolved state..

The concentrate was frozen in a controlled manner under the conditions described in Example I.

Example IV

20 kg of cod waste was. extracted with 200 kg of chilled 0.ln sodium hydroxide using a "Silverson" mixer. The mixture was then neutralized to pH 7.0 with 4N hydrochloric acid. 1.45 kg of NaCl was then added to the solution and dissolved. The insoluble material was removed as indicated in Example I. The clear solution was then concentrated by ultrafiltration. The pH value was adjusted to 6.5, and the concentrate, which contained approx. 3.4% protein, of which more than 50% was present in the dissolved state, was exposed

for freezing/texturing as described in example I.

Example V

5 kg of soy fluff was mixed with 50 kg of tap water and centrifuged to remove insoluble material. Sodium chloride was

added to the mixture to obtain a 4% salt solution. The pH value was adjusted to 7.5 with sodium hydroxide. The solution was

concentrated to a protein content of 14.2% of which more than 50% was in the dissolved state. The concentrate was frozen in a controlled manner as described in example I and freeze-dried.

The freeze-dried material was heat-set in a moist atmosphere at 115°C. the product was completely rehydrated in cold water or in a saline solution.

Example VI

The procedure from Example V was followed, with the exception that the concentrate was subjected to centrifugal freeze-drying.

Example VII

The procedure for extracting soy protein according to Example V was followed. The insoluble material was removed and the solution's pH value adjusted to 6.5. The solution was concentrated to obtain a concentrate with approx. 14% protein. To this concentrate was added 1% dialdehyde starch, based on the weight of the protein. The mixture was frozen in a controlled manner as described in example I and then heated at 115°C in a moist atmosphere. The dried product was rehydrated in cold water.

Example VIII

1 part by volume of meat protein extract, obtained by following the method from example I, and 3 parts by volume of soy protein extract, obtained by following the method from example V, were mixed and then concentrated by ultrafiltration to obtain a concentrate containing approx. 13% protein, of which at least 90% was present in a dissolved state. The pH value was approx. 6.5. The mixture was frozen in a controlled manner, heat-set and rehydrated according to the procedure from example I. Example IX 1 part by volume of the fish protein extract obtained in example IV was mixed with 3 parts by volume of the soy protein extract obtained as stated in example V. The mixture was concentrated to obtain a common concentrate containing 16% protein, of which approx. 70% was present in a dissolved state. The pH value was adjusted to approx. 6.5. The protein concentrate was frozen in a controlled manner as indicated in example I, then freeze-dried and heat-set at 115°C.

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Claims (17)

1. Process for the production of textured nutrient, characterized by freezing in a controlled manner a protein solution, in which the protein is mainly present in a dissolved state, into crystal layers of solvent which are separated by intermediate crystalline-cast protein layers which extend in one direction generally normal to a cooling surface, bringing at least a portion of the surface area of the proteinaceous material into contact with the cooling surface, and stabilizing the • developed structure. 2. Method as stated in claim 1, characterized in that an aqueous protein solution is used, in which more than 50% of the protein is present in a dissolved state. 3. Method as stated in claim 2, characterized in that 70-100% of the protein is present in a dissolved state. 4. Method as stated in any of the preceding claims, characterized in that the total protein content is at least 3 percent by weight. 5. Method as stated in claim 4, characterized in that the total protein content is from 10 to 30 percent by weight. 6. Method as stated in any of the preceding claims, characterized in that a solution of proteins of different origin is used. 7. Method as stated in claim 6, characterized in that a solution containing fish and soy proteins is used. , 8. Method as stated in claim 6, characterized in that a solution containing meat and soy proteins is used. 9. Method as set forth in claim 1, characterized in that the developed structure is stabilized by heat solidification of the frozen solution between 80 and 125°C. 10. Method as stated in any of the preceding claims, characterized in that a solution of myofibrillar proteins with a pH value of 5.7 to 6.5 is frozen in a controlled manner and then heat-solidified between 80 and 125°C . 11. Method as stated in any of the preceding claims, characterized in that the developed structure is stabilized by freeze-drying the frozen solution. 12. Method as stated in claim 1, characterized in that the development of structure in the protein solution and the stabilization of the structure that is achieved are carried out in one operation by subjecting the protein solution to centrifugal freeze-drying. 13. Method as stated in claim 12, characterized in that the freeze-dried material is further stabilized by heat setting between 80 and 125°C in a moist atmosphere. 14. Method as stated in claim 1, characterized in that the protein solution contains as a stabilizer a cross-linking agent which has been added to the protein solution before the solution was frozen in a controlled manner. 15. Method as stated in claim 14, characterized in that dialdehyde starch is used as cross-linking agent. 16. Method as stated in claim 15, characterized in that 0.5-10% dialdehyde starch is used based on the weight of the protein. 17. Method as stated in claim 15, characterized in that 0.6-1.5% dialdehyde starch is used based on the weight of protein.