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Lysozyme and its application in food preservation (Part 1)

Abstract: This paper summarizes the structure, source, activity determination method and application in food research of lysozyme, and prospects the application and development of lysozyme in food industry in the future according to the current research status

key words: lysozyme; Food industry; Lysozyme (ec3.2.1.17), namely n-acetylmuramidase, was used to act on the interaction between n-acetylmuramidase (NAM) and N-acetylglucosamine (NAG) in bacterial cell wall β- 1,4-glycan bond is widely distributed in various organisms in nature [1]

the study of lysozyme originated from the dissolution factor of Bacillus subtilis published by Nicolle (1907). In 1909, lashtschenko pointed out that the strong antibacterial effect of egg white was due to the action of enzymes. In 1922, Fleming found that human nasal mucus, saliva, tears, etc. also have strong bacteriolytic activity, and named its bacteriolytic factor lysozyme. Since then, the research on lysozyme has begun, and new progress has been made continuously. From 1959 to 1963, Salton et al. Clarified through a large number of studies that lysozyme is a kind of enzyme that can cut off the interaction between N-acetyl teichoic acid and N-acetylglucosamine β- Enzyme of 1,4 sugar sweet bond. In 1967, Philip group published the research on X-ray diffraction of egg white lysozyme substrate complex, introduced the structure of its catalyst, and became one of the major achievements in modern enzyme chemistry research. Since 1960, the research on microbial lysozyme has made rapid progress. Lysozyme has become a very powerful tool enzyme for studying the structure of cell wall, which not only helps people understand the fine structure of cell wall, but also greatly promotes the development and research of new lysozymes. With the deepening of research, it is found that lysozyme not only dissolves the bacterial cell wall, but also acts on the fungal cell wall. At the same time, we have a further understanding of its mechanism. Lysozyme can be applied in many fields, such as in medical treatment, it can interact with the viral structure in the blood to prevent the reproduction of influenza, adenovirus, etc; It can decompose mucopolysaccharide, which is conducive to the discharge of pus; It can remove necrotic tissue, enhance the efficacy of antibiotics and promote the reproduction of beneficial intestinal bacteria such as lactic acid bacteria. In recent years, people have applied lysozyme in food industry and bioengineering according to its bacteriolytic properties, especially in food industry, which shows a good prospect for the application of lysozyme

1 types and mechanism of action of lysozymes

lysozymes can be divided into two categories according to the different microorganisms they act on: bacterial cell wall lysozymes and fungal cell wall lysozymes. Bacterial cell wall lysozymes are subdivided into two kinds, one of which acts on β- The other is the cell wall lysozyme that acts on the "tail" end of the peptide chain and the amide part. Fungal cell wall lysozymes mainly include polyurethane (PU) and rubber products used in earthquake resistance, ballast pads, sleepers, etc., including yeast cell wall lysozyme and mold cell wall lysozyme [2]. Lysozyme comes from a wide range of sources, which can be extracted from the quality requirements of products, plants and microbial organisms that animal enterprises casually reduce in order to blindly reduce prices, and its mechanism of action is also different

1.1 egg white lysozyme

egg white lysozyme is a typical representative of animal lysozyme, and it is also the most deeply studied lysozyme at present. The content of lysozyme in egg white is about 2% - 4% [3], the isoelectric point is about ph10.8, and the molecular weight is 14000 [4], which can dissolve Gram-positive bacteria such as Micrococcus wallichii, Bacillus megaterium, and octopus flavus, and has no decomposition effect on Gram-negative bacteria. The mechanism of bacteriolysis is quite complex. Its optimum temperature is 50 ℃, and its chemical properties are very stable. The change of pH between 1.2 and 11.3 will not affect the structure of the enzyme, and the enzyme is also very stable in case of heat. In the range of pH4 ~ 7, the enzyme still has nearly 100% activity after being treated at 100 ℃ for 1min, but its stability is poor under alkaline environmental conditions. Egg white lysozyme is composed of 129 amino acids, and its stability is mainly maintained by four disulfide bonds, hydrogen bonds and hydrophobic bonds. Studies have shown that the primary structure of lysozyme in other bird egg whites is also 129 amino acids, but the amino acid arrangement is different and the active sites are also different

1.2 lysozyme of human and mammalian origin

lysozyme is found in human and mammalian secretions and body fluids. The primary structure of human lysozyme is arranged by 130 amino acids. There are four disulfide bonds, and the sequence and composition of the primary structure amino acids are very different from that of egg white lysozyme. However, the tertiary structure is similar, and the enzyme activity is nearly 2 times higher than that of lysozyme from egg white. At present, lysozyme has been isolated from a large number of animals. Research shows that its primary structure and physical and chemical properties are basically the same as human lysozyme, but its structure is not clear

1.3 plant lysozyme

at present, lysozyme has been isolated from papaya, turnip, fig and other plants. The bacteriolytic activity of plant lysozyme against Micrococcus wallichii is lower than that of egg white lysozyme, but its decomposition activity against colloidal chitin is about 10 times that of egg white lysozyme

1.4 lysozyme of microbial origin

it was found in the 1960s that some microorganisms can also produce lysozyme. At present, lysozymes produced by microorganisms are generally divided into the following five kinds: (1) internal n-acetylhexosamine enzyme, similar to egg white lysozyme, mainly destroys the β- 1, 4 sugar sweet bond. (2) Amidase mainly acts on the n-acetyl-l-alanine bond between N-acetyl-muramic acid (NAM) and peptide "tail" in bacterial cell wall peptidoglycan. (3) Endopeptidase breaks the peptide bond in the peptide "tail" and peptide "bridge". （4） β- 1，3、 β- 1,6 glucanase and mannanase are mainly used to decompose the cell wall of yeast cells. (5) Chitosanase is a lysozyme that breaks down the cell wall of mold

2 determination of lysozyme activity

there are usually two methods to determine lysozyme activity: (1) take the cell wall as the substrate, and express the enzyme activity by measuring the change of turbidity before and after its action. (2) The enzyme activity was expressed by the change of turbidity before and after the action with Micrococcus lysozyma culture medium as the substrate. Because both methods are solid-liquid two-phase reactions, it is difficult to accurately determine the reaction rate. So someone improved the method, using water-soluble polysaccharide GLYCOL CHITIN to prepare homogeneous substrate, and then use it to determine enzyme activity [4]

3 application of lysozyme in the food industry

in the food industry, lysozyme is a non-toxic protein, which can selectively dissolve the cell wall of the target microorganism and make it lose its physiological activity, while other nutrients in the food will hardly cause any loss. Therefore, it can safely replace chemical preservatives harmful to human health (such as benzoic acid and its sodium salt), so as to prolong the shelf life of food. It is a good natural preservative [5]

3.1 used for fresh-keeping and antisepsis of aquatic products

lysozyme itself is a non-toxic and harmless protein, and has a certain health care effect. It can selectively and purposely kill microorganisms without acting on other substances in food, so as to ensure that the original nutritional components of food are not lost. It has strong decomposition effect on Bacillus subtilis and radiation resistant Micrococcus among Gram-positive bacteria. It can also dissolve Gram-negative bacteria such as Escherichia coli, common Proteus and Vibrio parahaemolyticus to a certain extent. The optimum action concentration is 0.05%, which can be used in combination with phytic acid, polyphosphate, glycine, etc. to improve its anti-corrosion effect [6], and can be used for the preservation and anti-corrosion of cooked aquatic products and meat products. Mameihu [7] et al. Studied the effect of single factor of GNA solution, lysozyme and nisin on the fresh-keeping effect of chilled meat. The study showed that the fresh-keeping effect of lysozyme in single factor test was significantly better than that of the control group, significantly better than that of GNA group, and slightly better than that of Nisin group

mameihu [9] and others successfully studied a pure natural chilled meat preservative hnsafety-008 chilled meat preservative. The preservative is completely composed of safe, non-toxic and natural substances. The shelf life of the preservative can be extended by 1 ~ 4 times. The preservative can withstand the temperature below 95 ℃ and maintain its stability. Therefore, it can be added to the raw meat for low-temperature heating (about 80 ℃), and the use concentration is 0.05% - 0.01% of the meat weight. The use method is to add it when the meat is rolled or the travel problem is an important step in the selection of tensile testing machine. However, the problem to be noted is that in the hot processing of low-temperature meat products, the processing temperature should not exceed 95 ℃