Chitosan, also known as deacetylated chitin, is the second most abundant biopolymer in nature after cellulose, and is widely distributed, mainly in the shells of many lower animals, especially arthropods such as shrimps, crabs, insects, etc., and also in the cell walls of lower plants such as bacteria, algae and fungi. It is estimated that the annual biosynthesis of more than 1 billion t, is a huge renewable resource. The product of chitin after removing the acetyl group is chitosan.

Inhibitory mechanism of chitosan

Chitin, chitosan and their derivatives are antibacterial to many microorganisms such as bacteria, yeasts and fungi. The exact mechanism of chitosan’s antimicrobial activity is not yet fully understood, but various theories have been proposed.

The interaction of positively charged chitosan molecules and negatively charged microbial cell membranes results in the leakage of protein-like components from the cells. Chitosan has a chelating effect and selectively chelates some metal elements, thereby inhibiting microbial growth and toxin production.

Chitosan also activates some defense mechanisms in host tissues, acts as a water retainer and inhibits the activity of some enzymes. By penetrating chitosan into the nucleus of microorganisms, chitosan binds to DNA, thus inhibiting mRNA and protein synthesis. chitosan has better solubility and bacteriostatic properties than chitin due to the positive charge of the glucosamine monomer at the C2 position of chitosan when the pH is lower than 6 .

Bacteriostatic effect of chitosan

According to Japanese reports, chitosan has an inhibitory effect on Staphylococcus aureus and Escherichia coli. It has been reported that chitosan has strong inhibitory effect on five common food poisoning bacteria, namely Staphylococcus aureus, Escherichia coli, Yersinia coli, Salmonella typhimurium and Listeria monocytogenes. Japan has patented chitosan as a food preservative.

Application of chitosan in food preservation

1. Application in meat products preservation

Research has shown that chitosan has obvious freshness preservation effect on cooled pork. With 1% chitosan solution and 2% acetic acid solution mixture of non-vacuum packaging of pork preservation research, found in 10 ℃ with chitosan acetic acid solution treatment of pork storage after 12d the number of stray bacteria is only 5.51 logarithmic value (the control group for the value of 9.36 logarithmic value); in 20 ℃ chitosan mixture can still extend its storage period of 2d.

Some studies have shown that the higher the degree of deacetylation of chitosan, the better the preservation effect of chitosan, the proportion of free amino acid 0.62% chitosan solution (concentration of 1%, dissolved in 2% acetic acid) can make the shelf life of cooled meat up to 9d; the higher the concentration of chitosan, the better the effect of bacteriostatic inhibition, 1.5% chitosan 1% acetic acid solution can be used to make the shelf life up to 6d. water-soluble chitosan preservation effect is slightly lower than the acid-soluble chitosan. 2.5% water-soluble chitosan can make the shelf life up to 5d.

Chitosan and its oligosaccharide fresh beef, the method is to spray beef with 95% ethanol, vitamin E, hydrolyzed chitosan, chitosan and its oligosaccharide, hydrolyzed pectin and / or lysozyme mixture, beef preserved 3d microorganisms than the control group is less.

Some people have studied different degrees of polymerization of 0.25% chitosan 1% acetic acid solution on fresh Spanish mackerel, small yellowtail and fresh pork preservation effect, the results show that the low degree of polymerization of chitosan preservation effect is better; at the same time, but also studied the preservation of shrimp, the results of the chitosan is better than the phytic acid and sodium bisulfite and other preservatives.

2. Food packaging containers preservation

Chitosan and resin together with kneading and extrusion preparation of food containers, at least in the inner layer of the container contains chitosan, it will inhibit the growth of lactobacilli and thus prolong the food preservation time. Chitosan lactic acid solution infiltrated by the regeneration of cellulose fibers made of nonwoven fabrics and the formation of fresh materials, from which the meat, fish and other food packaging, can absorb the seepage and prevent the growth of staphylococcus bacteria, Escherichia coli and other microorganisms.