Transglutaminase (EC is a transferase enzyme catalyzing the acyl-transfer reaction. It catalyzes the formation of a covalent bond between primary amines and the gamma-carboxyamide group ofprotein- or peptide-bound glutamine (see Figure

The enzyme is widely distributed in nature: mammals (brain, liver, muscle, etc.), birds (blood), fish (muscle, blood), shellfish (muscle), plants microorganisms.

Its main use in the food industry is to process meat products.

Its application in dairy is due to its ability to transform a protein sol in a protein gel without heating. It reacts very well with casein and sodium caseinate; it may react also with alfa-lacto albumin or beta lactoglobulin depending on conditions. Its pH optimum range is between pH 5 and 8 and its optimum temperature range is between 40° and 50°C. It is quickly denatured at higher temperatures (more than 60°C), and it is unstable at pH lower than 4.5.

The acyl-transfer reaction of transglutaminase

Figure The acyl-transfer reaction of transglutaminase.

It may be used in yogurt, cream cheese, and fermented milk manufacture to improve milk protein functionality. It can also help when milk foam is requested (e.g., Cappuccino). Also, some types of cheese can benefit from the use of transglutaminase.

Gelation of milk proteins can be achieved by heat treatment—however, cold gelation has some advantages. Using cold gelation instead of heat induced gelation, we can prepare gels of comparable firmness with much less protein (3% whey protein required for heat-set gel, 0.5% whey protein required for cold-set gel), maximize functionality of all whey proteins (100% of protein contributes in cold-set gel, only 50% to 70% of protein contributes in heat-set gels).

Its application in set yogurt is due to increased gel strength, reduced syneresis, smooth, dry surface, reduction or elimination of added dry matter. In stirred yogurt, it is possible to obtain increased viscosity, improved creaminess, reduced syneresis, reduction of added dry matter or stabilizers.

In cow, goat, and sheep raw milk, there is a low-molecular-weight compound that inhibits transglutaminase activity. Heat treatment of milk eliminates this inhibition.

Generally, the advantage is that the protein/casein content of a product can be reduced and its moisture content increased without syneresis, so consumers perceive that it is better.

Other applications in dairy are for production of Tvorogh, Quark, Rulo de Cabra (Spain), Cuajada lactica de cabra (Spain and France), cream cheese, sour cream, Burgos Cheese type, Queso fresco (South America), and Quesillo (South America).

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