What are the general physical and chemical properties of TGase and how is it used?

Introduction to TGase
Transglutaminase (TGase or TG), also known as transglutaminase, is a monomeric protein acyltransferase with an active center consisting of 331 amino groups with a molecular weight of approximately 38,000.
This enzyme is widely found in humans, higher animals, plants and microorganisms. The enzyme can cause cross-linking between or within protein molecules, linkage between proteins and amino acids, and hydrolysis of glutamine residues within protein molecules through molecular insertion, cross-linking reactions, and deamination. Through these reactions, the structure of protein molecules changes, which can make protein molecules from small to large, thus improving the structure and function of proteins, such as improving the foaming, adhesion, emulsification, gelation, thickening, and emulsion stabilization characteristics of proteins, which in turn improves the appearance, flavor, taste, and texture of protein-rich food products, and improves the functional properties of a wide range of proteins such as nutritive value, texture structure, taste and storage period, etc. After modified by TG, the gelatinization, plasticity, water holding, water solubility and stability of proteins will be improved.
Characteristics of TG enzyme
1、Strong adhesive force: the covalent bond formed between proteins catalyzed by TG is difficult to break under general non-enzymatic catalytic conditions, so the adhesive force of food components treated with the enzyme is extremely strong. After the minced meat is shaped by the enzyme treatment, it will not fall apart after freezing, slicing and cooking.
2, good pH stability: the optimum pH of TG crude enzyme is 6-7, but it has high activity in the range of pH 5.0~8.0. When the pH is lower than 5, the enzyme activity decreases rapidly, and when the pH is higher than 8 less than 9, the enzyme activity decreases slowly. This is consistent with the pH value of general protein food system, which is favorable for application in food production.
3、Strong thermal stability: It is found that the optimum temperature of TG crude enzyme is about 52℃, and it has high activity in the range of 42~57℃. Especially in the protein food system, the thermal stability of the enzyme will be significantly improved, and this characteristic makes it will not be rapidly inactivated by heat treatment in general food processing.
4、Safe to use: Since TG is widely found in animal tissues, people have been consuming food containing lysine isopeptide bonds catalyzed by TG, so the new food produced by TG with TG is not only safe for human body, but also conducive to human health.
Functions and Uses
The main functional factor of TG is glutamine transaminase, which is used for the production of new protein foods. It is widely used in meat products, dairy products, fish products, soy products and pasta products.
1、Improve food texture. It can improve many important properties of proteins by catalyzing the cross-linking that occurs between protein molecules. For example, when the enzyme is used to produce reconstituted meat, it can not only bond the minced meat together, but also cross-link various non-meat proteins to meat proteins, which significantly improves the taste, flavor, tissue structure and nutrition of meat products.
2、Improve the nutritional value of protein. It can covalently cross-link certain essential amino acids (such as lysine) to proteins to prevent the destruction of amino acids by the Melad reaction, thus improving the nutritional value of proteins. Glutamine transaminase can also introduce missing amino acids into proteins with undesirable amino acid composition, which is of particular interest to people in developing countries.
3.Formation of heat- and water-resistant membranes. Dehydration of casein cross-linked by the enzyme results in a water-insoluble film that can be broken down by pancreatic rennet protease, making it an edible film that can be used as a food packaging material. Used to encapsulate lipids or fat-soluble substances. Improve the elasticity and water holding capacity of food
4, TG also has some unique properties, it can be cross-linked to protein macromolecules through lysine molecules, to protect lysine in food from the destruction of various processing; TG can be used for embedding lipids and fat-soluble substances, which can make proteins form heat-resistant, water-resistant film; after using TG treatment, there is no need for heat treatment in the process of gel formation in proteins.
Use of TG enzyme
1. The optimum pH of TG is 6~7, so the environment where TG is used should be between pH 6~7 as far as possible, and it is better not to exceed the range of 5~8.
2. The activity of TG remains stable at 40℃, and gradually decreases after exceeding 40℃, the optimum temperature for a reaction time of 10 minutes is 50~55℃, with the extension of the reaction time, the optimum reaction temperature will be reduced, and the temperature is high due to the foodstuffs, especially fish, meat, dairy products and other foodstuffs are prone to deterioration, so the determination of the reaction temperature is the most critical and difficult to determine of all the factors. Under the premise of ensuring product quality, it directly affects the amount of TG added and its catalytic reaction time, generally, for fish and meat and other low-oil perishable products selected reaction temperature are lower (1-10 ℃), and the corresponding reaction time is longer (2-12 hours or more), generally speaking, the reaction temperature is not higher than 40 ℃.
3. Object of action. First of all, the target of TG is protein, which catalyzes the reaction of the “reactive” glutamine residues, so the content of protein and the content of the “reactive” glutamine residues have a great influence on the effect of TG, that is to say, not all proteins or protein-containing substances have a great influence on the effect of TG, that is to say, not all proteins or protein-containing substances have a great influence on the effect of TG. Therefore, both the protein content and the amount of “reactive” glutamine residues in the protein have a great influence on the effect of TG, which means that not all proteins or protein-containing foods are good substrates for TG.
Secondly, the existence of lysine residues is needed for the reaction to take place (otherwise the action of TG can only change the solubility of protein and its related properties), that is to say, the content of lysine residues that can be reacted also has a great influence on the cross-linking reaction of TG.
4, common TG good substrates are casein and its sodium salt in milk, gelatin and myosin in meat, soy protein 11s globulin and 7s globulin, so in order to achieve good cross-linking effect, can be appropriate to add TG in the action of the good substrates, which are most commonly used in the sodium caseinate and gelatin as well as inexpensive soybean proteins, where it is necessary to put forward in particular is:
(1) Some proteins can be deformed by taking the appropriate method of lactic digestion and heating, but it contains glutamyl residues and / or lysine residues are more, just because of the spatial structure and other relationships, they can not be catalyzed by the TG reaction, through the enzyme or heating denaturation of these residues will be exposed to become a “reactive” residues, such as Wheat disk protein, whey protein and so on.
(2) Protein residual peptides rich in reactive glutamyl or lysyl residues, such as glutamyl or lysyl peptides, can be added selectively to supplement the insufficiency of relevant amino acid residues in the target.