Method for preparing an emulsion of adjustable viscosity

Abstract: Preparation of a heat-stable oil-in-water emulsion of adjustably increased viscosity by carrying out the following steps: a) preparing a mixture to be emulsified, comprising 10-30 wt.% fat and 3-15 wt.% protein based on the total composition; b) subjecting this mixture to an emulsifying treatment under such conditions that a "coarse" emulsion is obtained; c) flow-heating the thus obtained emulsion to a temperature of 65-85°C, whereafter the product is maintained at this temperature for some time; d) homogenizing the product prior or subsequent to this flow-heating; e) acidifying the product thus obtained; f) heating the acidified product for a period of 1-5 minutes at a temperature between 80 and 100°C; g) cooling the acidified heated product to the desired packaging temperature; h) packaging the product thus obtained.

Description: This invention relates to the preparation of a heat-stable emulsion of adjustably increased viscosity. The invention also relates to the preparation of a foodstuff based on such emulsion. In the preparation of liquid foodstuffs, the structure or consistency is an important parameter in connection with the organoleptic sensation. Besides the taste, this consistency, typically also referred to as viscosity, determines the perception of a foodstuff to a considerable extent. The structure is mainly determined by the interaction between the different constituents and in particular that with water. The extent to which the water present can be bound is determinative of the height of the viscosity. In general, to obtain a desired structure, a thickening or gelling agent is added to the aqueous foodstuff. Examples of such thickening agents which, even in a minor concentration, are capable of binding much water and hence of structuring an aqueous foodstuff, are polysaccharides such as gums, starches and carrageenans. Accordingly, in the preparation of sour products such as dressings, it is particularly starch and gums that are used as thickening agents. However, these polysaccharides lack the ability to stabilize a dispersion of fat or oil in water, i.e., they are not emulsifiers. In contrast with these polysaccharides, protein, such as egg albumin, has both gelling and emulsifying properties. Because egg protein is relatively expensive and has good functional properties only in fresh condition, other, cheaper protein sources were looked for. This investigation was focused in particular on the applicability of whey proteins both as emulsifier and as thickener in the preparation of mayonnaise-like products. It is known that proteins and in particular whey proteins can form structures upon heating (cf. European patent specification 0 195 365 and "Zuivelzicht", 77, (30/31) 1985, pp. 634-637). However, this concerns exclusively stationary heating techniques, because it is known that structures of whey proteins obtained through heating are not resistent to shearing forces. A number of drawbacks are associated with such stationary heating. In the first place, by the use of this technique only small volumes can be prepared because heating occurs through conduction. Accordingly, this method is unsuitable for the preparation of an industrial semifinished product because it is practically impossible to prepare a volume in excess of one liter in this manner. Another drawback is that in the case of a somewhat larger volume the heat transfer through conduction gives rise to differences in structure at the periphery and in the centre of the packing. Moreover, heating in this manner imposes strict requirements on the packing material in which the batchwise heating occurs. Finally, the use of batchwise processes generally yields gelled products, whereas for foodstuffs a paste-like structure is generally more desired. European patent specification 0 129 346 describes the heating of product while flowing (referred to hereinafter as 'flow-heating') in the preparation of sauces, the formulation including the use of whey proteins to partly replace the fat. Although these proteins will contribute to the viscosity to some extent, the viscosity is apparently insufficient. This can be derived not only from the fact that the products to be prepared must incorporate a combination of thickeners such as starch, guar gum and locust bean gum, but also from the manner in which the product must be packaged. The fact is that after the heater the product is preferably packaged while hot, so that the product can set in the package. In addition, after the heater the product must be exposed to a minimum of shearing forces because otherwise the structure breaks and a thin product results. Finally, in order to meet the requirement that the time of contact with the wall be shorter than one second, only a swept-surface heat exchanger can be used in this method. The object of the present invention is to provide a method which, employed in a continuous process operation, yields stable and heat-resistent structures whose viscosity is adjustable within certain limits without using other constituents than proteins as thickener. The invention is based in particular on the insight that through a heat activation step proteins, and particularly whey proteins, can be brought into a condition such that upon subsequent flow-heating in an acid environment they acquire a structure of highly increased viscosity compared with the nonactivated native protein, this structure being so stable that after the heating step ingredients can be added to the cold emulsion. This last requires that the structure can be subjected to shearing forces. According to the invention a heat-stable oil-in-water emulsion of adjustably increased viscosity is obtained by carrying out the following steps: a) preparing a mixture to be emulsified, comprising 10-30 wt.% fat and 3-15 wt.% protein based on the total composition; b) subjecting this mixture to an emulsifying treatment under such conditions that a "coarse" emulsion is obtained; c) flow-heating the thus obtained emulsion to the "activation temperature" of 65-85°C, whereafter the product is maintained at this temperature for a time sufficient to effect a heat activation of the proteins; d) vigorously homogenizing the product prior or subsequent to this flow-heating, such that a "fine" emulsion is obtained; e) acidifying the thus obtained product with an edible acid at a temperature equal to or lower than the activation temperature mentioned in step c) to a pH value between 3.8 and 4.5; f) flow-heating the acidified product for a period of 1-5 minutes at a temperature between 80 and 100°C; g) cooling the acidified heated product to the desired packaging temperature; h) packaging the product thus obtained. In the method according to the invention, the activating heating treatment in step c) effects a decrease of the so-called N.S.I. The N.S.I. is the "Nitrogen Solubility Index", which is determined by the method as described by De Wit in "Nederlands Melk- en Zuiveltijdschrift, 42 (1988), page 157. This N.S.I., determined at a pH of 4.6, corresponds well with the extent of protein denaturation. In the method according to the invention, the decrease of the N.S.I. at an activation temperature of 72°C is approximately 15%. The deliberate partial denaturation of the whey protein before the final structuring is essential to the method according to the invention. This is in contrast with the generally accepted view that the whey protein should not be denatured before the final structuring. According to a preferred embodiment of the invention the mixture to be emulsified according to step a) comprises 10-20 wt.% fat and 5-10 wt.% whey protein. The emulsifying treatment according to step b) preferably occurs at a temperature between 50 and 65°C. The flow-heating treatment during step c) is preferably carried out at a temperature in the range of 65-80°C. The homogenization according to step d) is preferably carried out at a pressure of at least 15 MPa and a temperature of 60-85°C. The product thus homogenized is preferably cooled to a temperature below 20°C and in particular to a temperature below 10°C. During step e) acidification is effected to a pH value between 3.8 and 4.5. In principle any nutrient acid can be used for this purpose. In particular, lactic acid or citric acid can be used. The heating operation according to step f) preferably lasts a period of 2-4 minutes at a temperature of approximately 90°C and cooling according to step g) is preferably effected to a temperature below 10°C. The method according to the invention has the additional advantage that by virtue of its continuous character any desired packaging material can be used in step h). The whey proteins which are used in the method according to the invention may have been prepared by a method which is known per se. According to a suitable method of preparation, they are obtained by ultrafiltration, which may or may not be followed by diafiltration of cheese whey, for instance. These methods are known per se and described, for instance, in Neth. Milk Dairy J. 37 (1983) 37-41. The ultrafiltration leads to a particular ratio of the protein content to the solid content and hence to a particular ratio of whey protein to ash. It is customary to characterize whey protein concentrates (WPC) so obtained on the basis of the whey protein content, so that WPC-80, for instance, is a whey protein concentrate comprising 80% (undenatured) whey proteins. The whey proteins can also be obtained, for instance, by desugaring cheese whey, optionally in combination with desalting through electrodialysis or ion exchange, until a protein content, based on the solids, of preferably at least 35% is achieved. In the preparation of the whey proteins it is essential that the proteins be denatured to the least possible extent. In determining the N.S.I. (at pH 4.6) this value must preferably be above 75%. A WPC obtained through spray-drying, suitable for use in the method according to the invention, possesses a whey protein content between 40 and 95%. In the emulsion according to the invention, any fat or any oil, both of vegetable and animal origin, such as milk fat, can be used. It is also possible to use mixtures of such vegetable and animal oils and fats which are suitable for the preparation of foodstuff emulsions such as spreads and sauces. By virtue of its continuous character, the method according to the invention is so flexible that it is possible to prepare not only end products such as foodstuffs, and in particular spreads and sauces, but also semimanufactured products, such as base materials for the preparation of pharmaceuticals, for instance ointments, etc. The method is eminently suitable for the preparation of sauces, because no other thickeners than whey proteins need to be used therein. The invention will now be further explained in and by the following examples. Example 1 An emulsion was prepared starting from the following constituents and in the specified amounts: WPC 80 9.5 % Sunflower oil 15.0 % Glucose syrup DE 20 2.0 % Trisodium citrate 0.1 % Lactic acid (10%) 8.0 % Water 65.4 % For the preparation of the emulsion the WPC 80 and the sodium citrate were dissolved in water of 60°C, whereafter the oil, which had been priorly adjusted to a temperature of 60°C, was added. Then emulsification took place for 2 minutes, using a Silverson suspension-emulsifying appliance. Then the emulsion was heated to the activation temperature, whereafter homogenization took place at this temperature, using a homogenization pressure of 40 MPa. Then the emulsion was cooled to a temperature of 10°C, whereafter the glucose syrup was added as well as an amount of lactic acid such that the pH attained a value of 4.2. Then the emulsion was heated to a temperature of 90°C on a swept-surface heat exchanger, whereafter the emulsion was maintained at this temperature for 3 minutes, followed by cooling to a temperature of 10°C in a swept-surface heat exchanger, whereafter the product was aseptically packaged. In the preparation two activation temperatures were investigated, viz. 65°C (variant 1) and 72°C (variant 2). After 24 h storage at 5°C the viscosity was determined at 20°C, utilizing a rotary viscometer, type Haake Rotovisco RV 12 with measuring system SV1. The viscosity was calculated in each case at a shearing rate of 100 sec -1 . Thus the following results were obtained: Activation temperature 65°C 72°C Viscosity (Pa.s) 0.11 0.28 It appears from this value that when an activation temperature is selected where no protein denaturation occurs, the viscosity of the end product is low; a higher activation temperature yields a clearly increased viscosity. Example 2 The method as described in example 1 was repeated, but now an activation temperature of 72°C was selected, whilst the fat content was raised to 20% based on the total composition, so that 5% less water was added. The method was carried out according to two variants, sunflower oil being used in variant 1 and milk fat in variant 2. Otherwise the procedure was as described in example 1. In this case, too, the viscosity was determined after storage for 24 h at 5°C. The viscosity was determined at 20°C and a shearing rate of 100 sec -1 . The results are summarized in the following table. 20% sunflower oil 20% milk fat Viscosity (Pa.s) 0.89 3.2 Both products appeared to be eminently suitable as bases for sauces. Liquid components such as acids, juices and alcohol, but also solid components, for example cut vegetables, could be added without any difficulty and it was striking in particular that the viscosity remained sufficiently high and that the structure was maintained. The taste of the products so obtained was excellent too. It is not requisite to use a swept-surface heat exchanger for heating. It is also possible to use other heating appliances, known per se, whereby comparable products are obtained. This is demonstrated in the following examples. In the method according to these examples, use was made of a tubular heater for heating a product at a pH of 4.2. Example 3 An emulsion was prepared starting from the following constituents in the specified amounts by weight. WPC 80 9.5 % Water 65.4 % Trisodium citrate 0.1 % Sunflower oil 15.0 % Lactic acid (10%) 8.0 % Glucose syrup DE 20 2.0 % In the preparation of the emulsion the procedure was as described in example 1, but now the heating of the acidified product was not carried out in a swept-surface heat exchanger but in a tubular heat exchanger. The heating temperature was 90°C and the product was maintained at this temperature for 3 minutes. Three activation temperatures were investigated, as indicated hereinafter: Variant 1: 68°C Variant 2: 74°C Variant 3: 78°C After the samples had been stored at 5°C for 24 h, the viscosity was determined using the method as described in example 1. The results were as follows: Results: Activation temperature 68°C 74°C 78°C Viscosity (Pa.s) 0.61 0.74 0.92 These products, too, had a smooth appearance and a so-called smooth mouth feel. The taste was judged as excellent, the sensation being neutral to tart. According to a variant of the method according to the invention, the whey protein is activated after the homogenization. The coarse emulsion is first homogenized at 60°C, whereafter the fine emulsion is activated. In this way, too, an excellent result is obtained, as appears from the following example. Example 4 An emulsion was prepared starting from the composition and the percentages by weight as indicated in example 3. The whey protein concentrate and the sodium citrate were dissolved in water and heated to a temperature of 60°C. Thereafter the sunflower oil, which had been adjusted to a temperature of 60°C, was added, whereafter emulsification took place for 2 minutes using an Ultra Turrax appliance. The product thus obtained was homogenized at 60°C at a pressure of 40 MPa. This fine emulsion was flow-heated to the activation temperature, whereafter it was maintained at this temperature for 10 seconds. Then the emulsion, while flowing, was cooled to a temperature of 10°C. Then the glucose syrup was added as well as an amount of lactic acid such that the pH attained a value of 4.2. Then the emulsion was heated to a temperature of 90°C using a tubular pasteurizer, whereafter the mixture was maintained at this temperature for 3 minutes. Then, in a next section of the tubular pasteurizer, the product was cooled to 20°C, wherafter it was packaged aseptically. In this method three activation temperatures were investigated, viz.: Variant 1: 70°C Variant 2: 74°C Variant 3: 78°C The viscosity was determined in the same manner as indicated in examples 1 through 3 and the following results were obtained: Activation temperature 70°C 74°C 78°C Viscosity (Pa.s) 0.25 0.41 1.14 The quality of the above products was judged as excellent and the taste was found to be neutral. In particular, the products appeared to have a fine smooth structure and to give rise to an agreeable mouth feel. The viscosity according to variant 1 appeared to be on the low side for a sauce base; variant 2 appeared to be suitable for the preparation of thinner sauces, while variant 3 appeared to be suitable for the more viscous types.

Claims: A method for the preparation of an emulsion, characterized in that a heat-stable oil-in-water emulsion of adjustably increased viscosity is obtained by carrying out the following steps: a) preparing a mixture to be emulsified, comprising 10-30 wt.% fat and 3-15 wt.% protein based on the total composition; b) subjecting this mixture to an emulsifying treatment under such conditions that a "coarse" emulsion is obtained; c) flow-heating the thus obtained emulsion to a temperature of 65-85°C, whereafter the product is maintained at this temperature for a time sufficient to effect a heat activation of the proteins; d) homogenizing the product prior or subsequent to this flow-heating; e) acidifying the thus obtained product at a temperature equal to or lower than the temperature mentioned in step c) to a pH value between 3.8 and 4.5; f) heating the acidified product for a period of 1-5 minutes at a temperature between 80 and 100°C; g) cooling the acidified heated product to the desired packaging temperature; h) packaging the product thus obtained. A method according to claim 1, characterized in that the mixture to be emulsified according to step a) comprises 10-20 wt.% fat and 5-10 wt.% whey protein. A method according to claims 1-2, characterized in that the emulsifying treatment according to step b) occurs at a temperature between 50 and 65°C. A method according to one or more of claims 1-3, characterized in that the flow-heating of the emulsion during step c) occurs at a temperature of 65-80°C. A method according to one or more of claims 1-4, characterized in that the homogenization according to step d) occurs at a pressure of at least 15 MPa and a temperature of 60-85°C. A method according to one or more of claims 1-5, characterized in that the product homogenized according to step d) is cooled to a temperature below 20°C and in particular below 10°C. A method according to one or more of claims 1-6, characterized in that heating according to step f) takes place for a period of 2-4 minutes at a temperature of approximately 90°C. A method according to one or more of claims 1-7, characterized in that cooling according to step g) proceeds to a temperature below 10°C. An emulsion obtained by the use of the method according to one or more of claims 1-8. A foodstuff obtained by the use of the method according to claim 9.

Inventors: HEUVELMAN LAMBERTUS, KLARENBEEK GIJSBERT, VAN DEN BOOGAARD CORNELIS, HEUVELMAN, LAMBERTUS, KLARENBEEK, GIJSBERT, VAN DEN BOOGAARD, CORNELIS
Applicants: VER COOP MELKIND, VERENIGDE COOEPERATIEVE MELKINDUSTRIE COBERCO B.A.
Application year: 1993
Main classification: A23L1
IPC codes: A23L1, A23D7