What Is a Cryoprotectant?

Antifreeze, also known as antifreeze, is a type of substance added to other liquids (usually water) to lower its freezing point and improve its antifreeze ability. It also has the function of dissolving ice crystals and preventing them from growing. Mainly used in internal combustion engine refrigeration systems, but also in air conditioning systems, solar systems, snow melting systems and freeze drying.

With the development of China's economy,

The main protein in aquatic muscle is myofibrillar protein. During the frozen storage process, myofibrillar protein will be frozen and denatured, which shows that its solubility in dilute saline will decrease, ATPase activity will decrease, viscosity will decrease, protein molecules will aggregate, and its spatial three-dimensional structure will change. After the protein is denatured, the texture of the frozen aquatic product becomes dry and hard, the processing suitability is reduced, and the product lacks elasticity.

The freezing denaturation of aquatic products is mainly caused by one or more of the following factors. First, the bound water in the muscles of the aquatic product is detached during freezing, which results in the formation of disulfide bonds within the molecule and denatures the protein aggregation. Secondly, the ice crystals formed during aquatic products damage the structure of proteins, and the growth of ice crystals causes the chemical bonds in protein molecules to be broken, causing protein denaturation. Third, the free water in the cells of the aquatic product forms ice crystals during freezing, which leads to the concentration of the cell fluid, the increase of the ion concentration, the change of the intracellular pH, the decrease of the enzyme activity and the denaturation of the protein. Fourth, the fatty acids in muscle tissues undergo oxidative degradation during frozen storage, producing harmful substances such as low-molecular aldehydes and ketones, which induce cross-linking of proteins and lipids, leading to denaturation of proteins. Fifth, the structure of some proteins in aquatic product muscle tissue is unstable and prone to denaturation, which significantly reduces Ca ²⁺ -ATPase activity, changes salt solubility, and reduces muscle water holding capacity.

Carbohydrates such as sucrose, maltose, lactose, and sorbitol, which are commonly used as antifreeze agents, can effectively prevent freeze denaturation of proteins in aquatic products to a certain extent. Studies have shown that sugars can change the state of bound water embedded in protein molecules, replace the bound water on the surface of protein molecules and bind to them, and have the effect of inhibiting protein denaturation. The greater the number of hydroxyl groups contained in the carbohydrate molecule, the greater the inhibitory effect on freezing denaturation of the protein. Under the same conditions, sorbitol and sucrose have stronger antifreeze effects, which may be related to the coordination of hydroxyl groups in sugar molecules. In order to strengthen the anti-freezing effect of fish, shrimp and their products, generally, when adding sugars, a complex phosphate is also added to form a compound. Its mechanism of action is mainly reflected in the following aspects. First, the complex phosphate solution is weakly alkaline, which can increase the pH of aquatic products. In addition, the complex phosphate solution has a buffering effect, which can maintain the neutral state of the aquatic products after addition, and reduce the lactic acid produced by the aquatic products on myofibrillar protein. Destruction and reduction of gel strength, at the same time, myofibrillar protein has the lowest degree of freeze denaturation when it is neutral, has good water retention performance, can maintain a good texture, and has the most significant antifreeze effect. Secondly, the addition of complex phosphate can increase the spatial structure of protein molecules, which can contain more water molecules and enhance the water retention of aquatic products. Third, complex phosphates can also chelate metal ions, especially calcium and magnesium ions. The formation of metal chelates can increase the probability of exposure of polar groups in protein molecules, which is easy to form. The water-absorbing sol is beneficial to the elasticity of the product. However, the effect of using complex phosphate alone on inhibiting the freeze denaturation of proteins in aquatic products is not obvious ^[2]

There are four main types of commonly used antifreeze: sugar antifreeze, complex phosphate antifreeze, protein hydrolysate antifreeze, and antifreeze protein. Aquatic products that use antifreeze to prevent freezing denaturation during freezing include: white prawn, carp, catfish, white mullet, clam, scallop, and bitch, etc. The research mainly focuses on the types and concentrations of antifreeze, The effects of freezing speed of aquatic products, frozen storage conditions and the concentration of antioxidants on the freezing denaturation of aquatic products. Tests have shown that aquatic products treated with antifreeze and then frozen can increase Ca ²⁺ -ATPase activity and increase the pH of samples; The nutrient content of the material is better maintained; the growth of ice crystals is reduced, the muscle tissue is reduced from mechanical damage, the integrity of the cells is better protected, and the effect of inhibiting the freezing denaturation of the protein is achieved.

Carbohydrate antifreeze

The mechanical damage suffered by the ice crystal growth during the cryopreservation of P. vannamei resulted in freeze denaturation of the protein, reduced the physical properties of the prawn, such as elasticity, tenderness and shear force, and increased the loss of juice, resulting in prawn nutrition. Reduced value. The addition of saccharide antifreeze agents such as oligosaccharides, seaweed gums and seaweed polysaccharides can effectively protect the quality of frozen shrimp and inhibit the frozen denaturation of shrimp proteins. Among them, 0.5% trehalose treatment had the most significant effect on reducing the thawing juice loss of P. vannamei.

Hydrolysates of crustaceans have a significant effect on freezing denaturation of aquatic myofibrillar proteins. Adding the hydrolysate of king crab crab shell to the myofibrillar protein of giscus fish effectively inhibited the decrease of Ca ²⁺ -ATPase activity and kept the water retention of frozen products better. The application of antifreeze suppresses the growth of ice crystals, reduces mechanical damage to muscle tissue, and has the effect of inhibiting the freezing denaturation of proteins, thereby maintaining the quality of frozen fish better.

The effect of 1% trehalose treatment on inhibiting surimi protein denaturation was not as good as that of 5% and 10%, and there was no significant difference in the dissolution amount of carp surimi salt-soluble protein after 5% and 10% trehalose solution impregnation. The carp surimi group immersed in a 5% trehalose solution had a salt-soluble protein content of 16.16% higher than that of the control group after 7 weeks of freezing; its myofibrillar protein Ca ²⁺ -ATPase enzyme activity was significantly higher than that of the control group.

2. Compound phosphate antifreeze

Sodium pyrophosphate and sodium tripolyphosphate compound antifreeze can effectively prevent the deformation of shellfish tissue structure. Different antifreeze formulations have different denaturation of protein in P. spp., Among which 0.4% compound phosphate treated The Ca ²⁺ -ATPase activity of C. corrugata was 87.9% after 2 months of frozen storage, and the effect of frozen storage was the best.

The effects of different antifreeze ratios of sodium pyrophosphate and sodium tripolyphosphate on the protein degeneration and tissue structure of the scallop shell muscle were studied. Studies have shown that: with the addition of antifreeze, the content of salt-soluble protein in the muscle of the scallops of the scallops after 6 months of frozen storage is higher than that of the control group; the rate of amino acid loss is significantly reduced; the growth of ice crystals is reduced, and the muscle tissue is affected Damage protects the integrity of the cell. The addition of complex phosphate antifreeze destroys the reticular structure of shellfish muscle proteins, so that the polar groups embedded in the structure are released, which improves the water retention performance of the muscle and significantly improves the quality and resistance of its frozen products. Possession ability.

3. Protein hydrolysate type antifreeze

Adding more than 5.0% squid hydrolysate can effectively inhibit the reduction of Ca ²⁺ -ATPase enzyme activity and water retention of dog females. The ATPase activity of the 10% protein hydrolysate sample can be maintained at 79.5%, and the mechanical damage of muscle tissue is significantly reduced, which can effectively prevent the frozen denaturation of the protein.

The protein hydrolysate can significantly inhibit the reduction of myofibrillar protein ATPase activity and water holding capacity, greatly reduce the degree of protein denaturation of frozen aquatic products, and greatly improve the quality and storage resistance of frozen products.

The effect of the hydrolyzed products of different types of proteolytic enzymes on the resistance of red carp fish steaks to preventing the frozen denaturation of carp surimi protein was studied. The results showed that the antifreeze surimi had higher Ca ²⁺ -ATPase enzyme activity after thawing than the samples without antifreeze, the antifreeze surimi K value decreased significantly, and TVB-N after thawing The value was significantly lower than that of the control group. The addition of antifreeze can suppress the spoilage of surimi after thawing, and maintain the freshness and elasticity of surimi.

4. Antifreeze protein

The addition of antifreeze protein can form a dense and uniform gel network structure inside the surimi, which can inhibit the loss of water. The addition of 5% antifreeze protein has a significant effect on inhibiting the increase of water loss rate. In addition, the addition of antifreeze protein can improve the properties of surimi gel, and it can better maintain the breaking strength, gel strength, and sag of surimi. Compared with traditional commercial antifreeze agents, antifreeze proteins can effectively change the structure of myrioglobin in catfish surimi, making it more stable and having better frozen stability.

Adding proline to frozen fish can effectively inhibit the decrease of Ca ²⁺ -ATPase activity, and better maintain the water retention of frozen products. It can be seen that proline has a better antifreeze effect. This may be because the proline causes the polar groups embedded in the protein structure to be released, which improves the water retention performance of the muscle, significantly improves the quality of the frozen product and its ability to store, and prevents the occurrence of freeze denaturation ^{[2 ]}

The research on antifreeze of aquatic products is relatively late, and there are not many in-depth studies. This is mainly related to the reasons and mechanisms for the freezing denaturation of proteins. The types and contents of proteins in different aquatic products are often different, and the degree of denaturation during freezing is also significantly different. What happens with each other is affected by many factors such as physiological conditions and freezing conditions. The research on frozen denaturation of aquatic products not only has important guiding significance for aquatic product processing technology, but also promotes the development of low-temperature biomedicine and enzyme technology. In the future, researchers can obtain the dynamic characteristics of protein molecule changes through laser confocal microscopy, and then clarify the process of protein denaturation of aquatic products, and clarify the molecular mechanism of frozen denaturation of aquatic products. The use of aquatic antifreeze can not only improve the quality of aquatic products and processed products, but also expand the aquatic product processing market, thereby increasing the application and demand for frozen aquatic product raw materials, and further enhancing the aquatic product processing industry in China. Therefore, the application of antifreeze in the frozen storage of aquatic products is of great significance ^[3] .