KR20090017691A - Milk product and method for its preparation - Google Patents

Abstract

A method of using tyrosinase for modifying the structure of milk products prepared from fat-reduced milk is disclosed. The method may be applied to raw or pasteurized fat-reduced milk, and it is used especially for preparing acidified milk products such as e.g. yogurt. Milk products with tyrosinase-modified structure are also disclosed.

Description

Milk product and method for its preparation

The present invention relates to dairy products with improved structure. More specifically, the present invention relates to the use of certain enzymes to modify the structure of dairy products. The invention relates in particular to the production of acidified dairy products such as yogurt. The present invention allows the use of fresh or pasteurized milk in place of more severely heat-treated milk.

Dairy products constitute an essential nutrient in the human diet. Milk is an excellent source of protein, which also generally contains vitamins and minerals such as calcium. Acidified dairy products typically prepared by lactic acid bacterial fermentation may also include lactic acid bacteria that promote health. Dairy products also contain animal fats, which make an important contribution to the texture of the product.

In addition to the chemical and biological components of dairy products, physical properties such as viscosity, thickness, firmness and moisture retention have a great impact on the quality of the product, and in particular on the texture. Texture is not only related to sensory perception but also to moisture retention, gelation, emulsification properties and stability. The separation of moisture from the product is a phenomenon called syneresis, which may involve the production of acidified dairy products. Syneresis is undesirable and should be avoided or at least minimized. A number of methods have been described for improving the physical properties of foods.

Milk gels are formed during acidification due to casein gelation. Heat treatment prior to acidification has been considered as an important step for the texture of acidic dairy products (Pereira et al., 2003). If the milk is not heated, only casein contributes to gel formation. After heat-induced denaturation, whey glycoproteins contribute to the texture formation of acidic milk gels by forming whey protein aggregates that are partially related to casein micelles and dispersed in a continuous casein network (van Vliet et al. , 2004).

Another attempt to improve the structure of yogurt and other dairy products is to raise the protein content or add thickeners such as polysaccharides, pectin, gelatin and other hydrocolloids, and starch. Thickeners increase the viscosity of yogurt, but unfortunately can be reduced due to sticky texture. A further disadvantage is generally the consumer's negative perception of food additives.

A more natural way of improving the properties of dairy products is to enzymatically modify them. Enzymes can be used to modify the technical properties of foods, for example, by enzymes that produce covalent crosslinks between amino acid residues in a protein or oxidize certain amino acid residues. Oxidation of amino acid residues may in turn also lead to the formation of crosslinks. Modification of proteinaceous materials by crosslinking is commonly used in food processing.

Enzymes proposed for food applications include transglutaminase, lipoxygenase, polyphenol oxidase (tyrosinase), peroxidase, lysyl oxidase, protein disulfide isomerase and sulfhydryl oxidase (see Matheis and Whitaker, 1987). Further proposed enzymes are laccases, bilirubin oxidases, ascorbic acid oxidases and ceruloplasmin, which cross-link plant and animal proteins such as, for example, grain proteins, casein, β-lactoglobulin and egg proteins. Has been proposed to make (see US2002 / 000970). Application of a specific crosslinking enzyme for a particular use depends on a number of factors such as the availability and accessibility of the substrate, possible interference compounds, the addition of external substrates, pH, temperature, inhibitors and the like.

Currently, only transglutaminase (TG, glutaminylpeptide: amine γ-glutamyltransferase, EC 2.3.2.13) has been intensively studied and is a commercially available enzyme for crosslinking milk proteins. The reactivity of the transglutaminase depends on the availability and accessibility of the target amino acids glutamine and lysine in the protein substrate.

The major proteins of cow's milk consist of a _s1- , a _s2- , β- and κ-casein, and the spherical whey proteins a-lactalbumin (a-La) and β-lactoglobulin (β-Lg). Casein is considered a very good substrate of transglutaminase, while the spherical whey proteins, a-La and β-Lg, have been found to be poor substrates. Partial unfolding of globular proteins by chemical modification with a reducing agent or by heat treatment has improved their susceptibility to crosslinking by transglutaminase.

Nonaka et al. (1992) have studied the reactivity of transglutaminase to casein in skim milk powder and compared it to the casein salt. These indicate that the reactivity of transglutaminase to casein in milk is poor compared to that for casein salts, indicating that casein in milk is not susceptible to enzymatic crosslinking in the same way as casein salts.

Heating milk prior to crosslinking with transglutaminase has been found to dramatically increase the reactivity of the milk protein. Preheating at 85 ° C. for 15 minutes has been found to improve the susceptibility of milk proteins to crosslinking (Shama et al. 2001). It has also been found that cow's milk heat-treated at low temperatures (63 ° C., 30 minutes) has a lower sensitivity to transglutaminase than cow's milk sterilized at 130 ° C. (2-3 seconds). When the former was further heat treated at 90 ° C., reactivity to the transglutaminase was significantly improved. It has been reported that preheating fresh milk at 95 ° C. for 2 seconds prior to reacting with glutaminase is effective for yogurt preparation (see US2002 / 0061358).

However, too much heat treatment before acidification and / or enzyme treatment is also associated with disadvantages. First, heat treatment is an additional step that complicates the manufacture of dairy products, of course the time and energy required increases the manufacturing cost. In addition, heat treatment denatures milk protein, resulting in adverse effects in loss of flavor, bitter taste and texture.

It has been reported that heat treatment can be avoided in connection with transglutaminase by adding reducing agents such as thiol compounds to milk. Reducing agents allow the use of transglutaminase in fresh milk without the need for preheating. Suitable reducing agents are, for example, glutathione, cysteine, γ-glutamylcysteine, sulfurous acid, ascorbic acid and erythorbic acid. Milk treated with transglutaminase in the presence of a reducing agent has been proposed for use in the manufacture of yogurt, cheese and milk powder to improve texture and texture (see US2002 / 0061358). However, the addition of reducing agents can be problematic because food additives should be avoided as much as possible. Reducing agents may also affect other properties of the final product, such as taste or flavor.

The present invention relates to a novel process for preparing structurally modified dairy products without the addition of harmful preheating or reducing agents associated with transglutaminase.

Tyrosinase is another crosslinking enzyme that has been proposed in food applications. Tyrosinase, for example, has been reported to affect wheat proteins (Takasaki and Kawakishi, 1997; Takasaki et al., 2001). Lanto et al. (Published) studied the effects of transglutaminase, tyrosinase and lyophilized apple ground powder on the structure and gel formation of homogenized pork. Tyrosinase could not affect gel formation in the tests performed, but this improved the gel hardness of unheated meat homogenates to a certain degree.

Tyrosinase has also been reported to crosslink with wheat proteins a-La and β-Lg in the presence of caffeic acid. In contrast to β-Lg, a-La could even be directly crosslinked by tyrosinase without the addition of caffeic acid (Thalmann and Loetzbeyer, 2002). In addition, the effects of tyrosinase on casein in the presence or absence of L-tyrosine and L-DOPA as crosslinkers have been studied. The presence of the crosslinker was found to be essential for the crosslinking of casein (Halaouli et al., 2005).

All of these references do not describe the use of tyrosinase in crosslinking proteins in milk. Applicants tried to do this, but the results were not good. As can be observed using transglutaminase, isolated milk proteins do not react in the same way they react in milk. Tyrosinase did not show significant crosslinking activity in whole cow's milk. Preheating the milk did not significantly improve crosslinking. Surprisingly, however, it has been found that the reduction in milk fat content results in a desirable modification of the texture of the product when tyrosinase is used. This was particularly surprising because fat loss generally has an adverse effect on the texture and moisture retention of the product.

The present invention relates to a method for modifying dairy products, which is suitable for raw milk or low heat milk, which is moderately heat treated, and has an excellent texture deformation and anti-syneresis effect compared to transglutaminase. The method allows the use of pasteurized milk instead of using pasteurized and typically reheated milk and the production of dairy products with reduced fat and protein content without the need to add other additives such as thickeners.

Fats and added proteins, starches and polysaccharides in processed dairy products have a great impact on technical and sensory properties. The present invention now contributes to low energy dairy products suitable for weight control, for example, which are better for health and contain less additives.

Summary of the Invention

The present invention provides a method for producing dairy products, comprising adding tyrosinase to raw milk or pasteurized low-fat milk and incubating the same to form a dairy product having a modified structure.

The present invention also provides the use of tyrosinase in modifying the structure of fresh or pasteurized low fat milk.

The present invention also provides dairy products comprising fresh milk or pasteurized low fat milk and tyrosinase, and having a tyrosinase modified structure.

Certain embodiments of the invention are set forth in the dependent claims of the claims.

Other objects, details and advantages of the invention will be apparent from the following drawings, description and examples.

FIG. 1 shows SDS-PAGE gels of skim milk and preheated skim milk unheated without tyrosinase treatment or in the presence of 500 nkat tyrosinase / protein g.

2 shows the effect of tyrosinase on the firmness of 2.7% Na-casein salt gel.

3 shows the effect of tyrosinase (TYR) on the firmness of acidified milk gels prepared from pasteurized whole or skim milk.

4 shows the effect of tyrosinase (TYR) on the firmness of acidified milk gels prepared from pasteurized skim milk.

5A shows the effects of tyrosinase (TYR) and transglutaminase (TG) on the firmness of acidified milk gels prepared from pasteurized skim milk.

5B shows the effects of tyrosinase (TYR) and transglutaminase (TG) on liquids released from acidified milk gels prepared from pasteurized skim milk.

FIG. 6 shows two Trichoderma reesei ) shows amino acid sequence alignment of tyrosinase TYRI and TYRII. The sequence is shown up to the C-terminal cleavage site of TYRII. The signal sequence is in the first column. The putative propeptide cleavage site of TYRI is indicated by the arrow. Amino acid residues contained in the coordination of two Cu atoms in the active site were darkened. The thioether bond between cysteine and histidine contained in the activation site of tyrosinase is shown by the vertical lines above the sequence.

Tyrosinase belongs to the group of phenol oxidases that use oxygen as the electron acceptor. Typically tyrosinase can be distinguished from other phenol oxidases, ie laccases, based on substrate specificity and sensitivity to inhibitors. However, at present it is distinguished based on structural features. Structurally, the main difference between tyrosinase and laccase is that tyrosinase has a binuclear copper moiety with two type III copper at its active site, while laccase has a total of four copper atoms (type I and zero) at its active site. Copper type II, and a pair of type III coppers).

Tyrosinase oxidizes various phenolic compounds to the corresponding quinones. Quinones are highly reactive and can also react non-enzymatically. Representative substrates of tyrosinase are first tyrosine (or tyrosine residues in protein) which are first hydroxylated with DOPA (dihydroxyphenylalanine or DOPA residues in protein) and then further oxidized by enzymes to dopaquinones (or dopaquinone residues in proteins). )to be. Dopaquinones can react non-enzymatically with many chemical structures such as other dopaquinones, thiols and amino groups. Thus, tyrosinase has one and two enzymatic activities in the same protein, namely monophenol monooxygenase activity (EC 1.14.18.1) and catechol oxidase activity (EC 1.10.3.1) as shown below.

The substrate specificity of tyrosinase is relatively broad, and enzymes can oxidize many polyphenols and aromatic amines. However, in contrast to laccase (EC 1.10.3.2), tyrosinase does not oxidize cyringalazine. At least tyrosine, lysine and cysteine residues in the protein form a covalent bond with the dopaquinone formed by tyrosinase.

Tyrosinase activity can be measured by techniques generally known in the art. L-DOPA or L-tyrosine can be used as the substrate, after which dopachrome formation can be monitored spectrophotometrically, or alternatively, substrate consumption can be monitored with subsequent oxygen consumption.

Tyrosinase is widely distributed in nature and is found in animals, plants, fungi (including mushrooms) and bacteria. The only commercially available tyrosinase originates from the mushroom Agaricus bisporus . Tyrosinase used in the present invention may be derived from any animal, plant, fungus or bacterium capable of producing tyrosinase. According to one aspect of the invention, tyrosinase is of microbial origin. Tyrosinase, for example, Neurospora crassa), Streptomyces (Streptomyces), Bacillus (Bacillus), Mai in table Titanium (Myrotheium), non-cor (Mucor), pre OKO glutamicum (Miriococcum), Aspergillus peogil Ruth (Aspergillus), a car sat Thomas thiazole (Chaetotomastia ), Ascovaginospora , Chaetomium , Trametes , Serpula Serpula lacrymans ), Conidiophora puteana ), Pycnoporus , Scytalium and Trichoderma . According to certain embodiments of the invention, tyrosinase originates from filamentous fungi. Suitable tyrosinase is described in PCT / FI2006 / 050055. Tyrosinase can be, for example, extracellular tyrosinase, or a tyrosinase variant thereof, obtainable from Trichoderma reesei. According to certain embodiments of the invention, tyrosinase comprises an amino acid sequence of at least 70, 80, 90, 95, 98 or 99% identical to the amino acid sequence of TYR1 or TYR2 or fragments thereof having tyrosinase activity as shown in FIG. 6.

An effective amount of tyrosinase is added under conditions sufficient to modify the structure of the dairy product obtained in fresh or pasteurized low fat milk. The structure of a dairy product refers to both its chemical and physical properties. The structure affects the sensory perception of the product, the texture. The relationship between structure and water retention is complex and not inadequate, but as used herein, "structure" includes both texture and water retention properties.

Milk to be treated with tyrosinase is obtained from milk-squeezable animals, preferably cows or goats. Fat and oil are removed before the enzyme treatment to yield low fat milk. Milk may contain up to about 10% fat, but generally whole milk has a fat content of 3.5 to 3.6% by weight. In this regard, "low fat milk" refers to milk having a maximum fat content of 2.0% by weight. Preferably, it has a fat content of 1.5, 1.0 or 0.5% by weight or less. According to certain embodiments of the present invention, all fat is removed to obtain a "fat skim" having a fat content of 0% by weight. The manufacture of low fat milk, including skim milk, is a common knowledge.

As used herein, "fresh milk" refers to milk that has not been heat treated to reduce its biohazard.

"Cold pasteurized" milk refers to milk that has been adequately heat treated to destroy pathogens, undesirable enzymes and milk rot bacteria. Pasteurization is a term commonly used in dairy farming and refers to minimizing the heat treatment required to obtain microbiologically safe products with extended shelf life. The degree of microbe and enzyme inactivation depends on the combination of temperature and time. Heat treatment for about 30 seconds at 62-65 ° C. is used in some countries, while in other countries heat treatment is carried out for much shorter time at temperatures of 70-75 ° C. Milk is generally pasteurized at 72 ° C. for 15 seconds. Milk is judged to be pasteurized when tested negative for phosphatase but positive for peroxidase.

Both raw and pasteurized milk may undergo other processing such as centrifugation, filtration or homogenization prior to pasteurization and / or tyrosinase treatment. Conventional food additives may be added if desired.

Tyrosinase modified low fat milk can be used, for example, when preparing milk powder by spray drying. According to certain embodiments of the invention, tyrosinase modified low fat milk is used in the production of acidified dairy products such as yogurt, clabber milk, desserts, creme fraiche, fermented cream, and the like. . The preparation of these products is carried out in the absence of rennets or other proteolytic enzymes. Thus, the "dairy product" formed by the method of the present invention may be, for example, milk concentrate or milk powder, yoghurt, acidified milk, krem fresh, fermented cream, low fat cream, dairy desserts and the like.

As suggested above, pre-acidification heat treatment is considered to be essential for the texture of acid dairy products. If transglutaminase is used, heat treatment is also necessary to improve the susceptibility to crosslinking of milk proteins. In this regard, "heat treatment" or "preheating" is stronger than pasteurization and results in peroxidase inactivation. Typical preheating temperatures for different processes are 85 to 140 ° C., treatment times can vary from 30 minutes to several seconds, and typically 85 to 95 ° C. is used for 30 to 10 minutes. Skim milk is generally preheated at about 85 to 95 ° C. for about 5 to 15 minutes, and at higher temperatures the time is shorter.

Milk naturally contains about 3.2% protein. Yogurt is commonly prepared from milk having a protein content of 3 to 5% by weight or more, depending on the amount of other additives used, such as hydrocolloids and starches, to obtain the desired texture. When no additives are used, the protein content is increased by about 5%, for example by evaporation or by adding an external protein. The pasteurized milk, optionally with increased protein content, is heat treated at about 90-95 ° C. for about 5 to 10 minutes and sugar, fruit, jam or other sweeteners may be added. The mixture is then cooled and seeded with starter, i.e., acid producing microorganisms such as lactic acid bacteria that contribute to both acidification and sweetness. Fermentation is generally carried out at 40 to 45 ° C. for 3 to 6 hours. Possible enzymes are added before or simultaneously with the starter. After fermentation, the yoghurt may be optionally further heat treated to extend its storage time. However, its post-heating can also be avoided in order not to destroy the fermenting organisms of the final product, which may have health promoting properties. For experimental acidification, D-gluconate lactone (GDL) can be used in place of fermenting organisms.

Dairy products oxidized according to the present invention can be prepared using tyrosinase in the same manner as described above, except that heat treatment above 80 ° C. is not performed prior to acidification. If the milk is already pasteurized on the farm, it can optionally be re-pasteurized in the milking parlor at a temperature not exceeding 80 ° C. prior to enzymatic treatment. Tyrosinase can be added before or after adding the starter. Conveniently tyrosinase is added simultaneously with the starter and allows it to react during lactic acid fermentation. Additional oxygen can be supplied to the reaction mixture to enhance the effect of the enzyme. Tyrosinase enables the use of milk having a protein content of less than 5% by weight, and in particular less than 4% by weight, for example about 3.2% natural protein, for the production of yogurt.

Tyrosinase is dissolved in aqueous solution. An amount of at least 10, 20, 40, 80, 120, 160, 320 or 640 nkat per gram of milk protein is generally sufficient to modify the texture and / or water binding properties of the dairy product. Tyrosinase is generally allowed to react for at least 10 minutes to 24 hours at a temperature of about 4 to 40 ° C. Naturally incubation at low temperatures requires longer incubation times and vice versa at high temperatures. Incubation times of at least 1 hour and 18 hours are typical at 4 ° C., while at 40 ° C., reaction times of 10 minutes to 4 hours are effective. The pH may range from 3 to 8, preferably 3 to 5, during the process. In some cases, the incubation is terminated by post heating, but this is not necessary.

Tyrosinase in particular alters the texture and moisture retention of dairy products. The effect of tyrosinase on protein in low fat milk can be observed, for example, as increased molecular weight, maximum compaction force or compressive area as measured by milk protein, and / or improved water retention. Moisture retention capacity can be measured, for example, as a liquid released from the crosslinked gel.

According to certain embodiments of the invention, live milk or pasteurized skim milk is inoculated with a microorganism capable of forming lactic acid to obtain a fermentation mixture, which is subjected to conditions sufficient to acidify the dairy product and alter its texture and water retention. Incubate in the presence of tyrosinase.

The invention is illustrated by the following non-limiting examples. However, it is to be understood that the aspects provided in the above description and examples are for illustrative purposes only and that various changes and modifications are possible within the scope of the invention.

Example  1. Tyrosine in heated and unheated dairy products Catalyzed  Crosslinking

A tyrosinase gene encoding a protein comprising the sequence of TYR2 as shown in FIG. 6 was amplified by PCR from the genomic DNA of Trichoderma reesei, and the isolated gene was overexpressed and grown in T. reesei under the CBHI promoter. Drained into the medium.

Tyrosinase activity was assayed using 15 mM L-DOPA (Sigma, USA) as substrate as per Robb (1984) at pH 7 and room temperature. Enzyme activity is expressed in nanocats (nkat). 1 nkat is defined as the amount of enzymatic activity that converts 1 nmol per second of the substrate used in assay conditions. Enzyme dose per gram of protein nkat refers to the amount of enzyme calculated and administered as activity per gram of milk protein.

Changes in the molecular weight and mobility of milk proteins caused by T. reese tyrosinase were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Tyrosinase was added to fresh milk or heated (90 ° C., 5 min) skim milk in an open tube (oxygen available) at a capacity of 500 nkat / protein g and the tube was sealed (less oxygen available). Incubation was performed at 30 ° C. for 2 hours.

The results are shown in FIG. Samples were as follows: Lanes 1 and 10: Molecular weight standard, Lane 2: Sealed tube unheated milk, Lane 3: Sealed tube unheated milk + Tyrosinase, Lane 4: Open tube unheated milk, Lane 5: open tube unheated milk + tyrosinase, lane 6: sealed tube heated milk, lane 7: sealed tube heated milk + tyrosinase, lane 8: open tube heated milk, lane 9: open tube Heated milk + tyrosinase, lane 10: molecular weight standard.

Tyrosinase caused the following detectable electrophoretic changes: 1) the appearance of a high molecular weight compound of about 198 KDa under the well, and 2) the loss of casein (especially in an open tube). The results indicate that tyrosinase can catalyze the formation of crosslinks in both unheated milk and heated milk, with this effect being greater in the presence of oxygen.

Example  2. Tyrosinase on  by Na Caseinate of protein Firm  Improving

Gels were prepared from Na-casein salt dissolved in tap water overnight at room temperature. The casein salt solution was chemically acidified during enzyme treatment with GDL (D-gluconate lactone; 0.4% GDL in 2.7% (w / w) casein salt, final pH 4.6 to 4.7). T. Reese tyrosinase (0, 10 and 50 nkat / g casein salt) and GDL are mixed in 13 ml of casein salt solution and an aliquot of 2.35 ml of solution is pipetted into a cylindrical aluminum container (16 mm diameter) It was. Samples were covered with glass petri dishes and they were incubated at 30 ° C. for 4 hours. The firmness of the gel after one day was determined by measuring the maximum compressive force required to compress the 5 mm gel (0.5 mm / s, 4 repeated samples) at room temperature (Texture Analyzer TA-HDi, Stable Micro Systems). . 4.5% casein salt gel was measured without enzyme treatment to compare the firmness. The result is shown in FIG.

Tyrosinase increased gel firmness at both doses. In addition, the firmness of the tyrosinase-treated 2.7% casein salt gel was about the same as that of the 4.5% casein salt gel without tyrosinase; The maximum compressive force for both samples was about 100 g, which indicates that the protein content of the gel can be reduced by using tyrosinase.

Example  3. Tyrosinase from whole milk and skim milk Catalyzed  Crosslinking

Tyrosinase from T. reesei is added to pasteurized whole milk (3.5% fat) and skim milk (0% fat) at a milk temperature of 40 ° C. at a dose of 50 nkat tyrosinase / g of protein and milk at 40 ° C. for 1 hour. Incubated. During incubation, the sample was continuously supplied with oxygen. In addition, a control solution without enzyme was prepared. The milk sample was then acidified at 40 ° C. for 4 hours using 1.2% GDL (final pH 4.6). After overnight storage at 4 ° C., the maximum compressive force was measured with a Texture Analyzer (TA-HDi, Stable Micro Systems). The results are shown in FIG. Tyrosinase significantly increased the firmness of the acidified milk gel. This effect was significantly greater when using skim milk than whole milk.

Example  4. Tyrosinase-induced crosslinking of pasteurized skim milk

Mushroom tyrosinase (Fluka, Switzerland) was added (50 nkat tyrosinase / protein g) to warm the pasteurized skim milk (40 ° C.) and the milk was incubated at 40 ° C. for 1 hour. During incubation, the sample was continuously oxygenated. In addition, a control solution without enzyme was prepared. Thereafter, the milk sample was acidified at 40 ° C. for 4 hours using 1.2% GDL (final pH 4.6). After overnight storage at 4 ° C., the maximum compressive force was measured with a texture analyzer (TA-HDi, Stable Micro Systems). The results are shown in FIG. Mushroom tyrosinase increased the hardness of the acidified skim milk gel.

Example  5. Tyrosinase Wow Transglutaminase  compare

Tyrosinase, or transglutaminase (Activa MP, manufactured by Ajinomoto) from T. Reesei was added at a dose of 50 nkat enzyme / protein, warming the pasteurized skim milk (40 ° C.) and milk Incubated at 40 ° C. for 1 hour. Tyrosinase activity was measured as described in Example 1, and transglutaminase activity was determined using 0.2 M N-carbobenzoxy (CBZ) -L-glutaminylglycine (Sigma, USA). Was measured at pH 6 using as substrate (Folk, 1970). One nkat defines the substrate used in assay conditions as the amount of enzymatic activity that converts 1 nmol per second. Enzyme dose nkat / g protein refers to the amount of enzyme calculated and administered as activity per gram milk protein.

During incubation, the sample containing tyrosinase was continuously oxygenated. In addition, a control solution without enzymes was prepared. The milk sample was then acidified for 4 hours at 40 ° C. using 1.2% GDL (final pH 4.6). After overnight storage at 4 ° C., the liquid released from the gel was slowly poured from the sample cup and weighed. Thereafter, the maximum compressive force was measured by a texture analyzer (TA-HDi, Stable Micro Systems).

Although the enzymatic activity of tyrosinase and transglutaminase is not directly comparable due to differences in reaction mechanism and model substrate, tyrosinase was found to be superior to transglutaminase.

The results of the compression test are shown in FIG. 5A. The firmness of the acid milk gel was greatly increased by the use of tyrosinase, whereas the gel containing transglutaminase was only slightly harder than the control gel without enzyme.

The amount of liquid released from the gel during overnight storage at 4 ° C. is shown in FIG. 5B. Water binding of the acid milk gel was reduced to zero by the use of tyrosinase. Transglutaminase did not prevent liquid release compared to the enzyme free control.

references

Claims (11)

Adding tyrosinase to raw milk or pasteurized low fat milk and incubating it to form a dairy product having a modified structure. The method of claim 1, wherein the acidified dairy product is prepared. The method of claim 2, wherein the acidified dairy product is yoghurt, clabber milk, creme fraiche, fermented cream or dessert. The process for producing dairy products according to claim 1, wherein the milk concentrate, milk powder or low fat cream is prepared. 2. The method of claim 1, further comprising inoculating live milk or pasteurized skim milk with a microorganism capable of forming lactic acid to obtain a fermentation mixture, and acidifying the dairy product in the presence of tyrosinase and the texture and moisture retention of the mixture in the presence of tyrosinase. Incubating under conditions sufficient to modify the strain. The method of claim 1, wherein the tyrosinase is of fungal origin. The method of claim 1, wherein the acidified dairy product, preferably a yogurt having a fat content of 2% or less and a protein content of less than 4%, is prepared. The method of claim 1, wherein the low fat milk is heat treated at a temperature not exceeding 80 ° C. before adding tyrosinase. Use of tyrosinase in modifying the structure of raw or pasteurized low fat milk. A dairy product comprising raw milk or pasteurized low fat milk and tyrosinase and having a tyrosinase modified structure. The dairy product of claim 10 which is an acidified dairy product.

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