Classification and characteristics of commonly used preservatives(3)

Streptococcus lactis

In 1969, the Joint Food and Agriculture Organisation/World Health Organisation (FAL/WHO) Expert Committee on Food Additives confirmed that Streptococcus lactis could be used as a food preservative, and in March 1992 the Chinese Ministry of Health approved the implementation of a document stating. "Streptococcus lactis can be scientifically considered safe as a food preservative". It can effectively inhibit the growth and multiplication of many Gram-positive bacteria that cause food spoilage, such as Clostridium botulinum, Staphylococcus aureus, Streptococcus haemolyticus, Listeria monocytogenes and Bacillus thermophilus, and is particularly effective against spore-producing Gram-positive bacteria. The antimicrobial action of Streptococcus lactis is through interference with the normal function of the cell v-membrane, causing permeation of the cell membrane, loss of nutrients and a decrease in membrane potential, leading to the death of pathogenic and spoilage bacteria cells. It is a non-toxic natural preservative that has no adverse effects on the colour, aroma, taste and texture of food. It is now widely used in dairy products, canned products, fish products and alcoholic beverages.

Natamycin

Natamycin is a white to creamy white, odourless and tasteless crystalline powder produced by the controlled fermentation of Streptomyces Natalis, usually in an enolic structure. Its mechanism of action is to bind to the ergosterol and other sterol groups of the fungus, blocking ergosterol biosynthesis and thus causing cell membrane distortion and ultimately leakage, resulting in cell death. The surface treatment of dough with natamycin in baked goods has a significant shelf-life extending effect. The addition of a certain amount of natamycin to the production of foods such as sausages, beverages and jams prevents mould without disturbing other nutrients.

Epsilon-mono-lysine

Research on ε-mono-lysine is well established abroad, especially in Japan, and is just beginning in China. It is a natural biometabolic product. It has good bactericidal ability and thermal stability, and is a biological preservative with excellent preservative properties and great commercial potential. In Japan, ε-mono-lysine has been approved as a preservative to be added to foods and is widely used in the preservation and preservation of instant rice, wet cooked noodles, cooked vegetables, seafood, sauces, soy sauce, fish fillets and biscuits. Xu Honghua et al. investigated the effect of ε-mono-lysine on the preservation of milk. When 420mg/L of ε-mono-lysine and 2% glycine were used in combination, the best preservation effect was achieved, which could be kept for 11d and still have high acceptability. It was also found that ε-mono-lysine and other natural antibacterial agents used in combination had a significant synergistic effect and could improve their antibacterial ability.

Lysozyme

Lysozyme is a non-toxic protein that selectively breaks down the cell wall of microorganisms and acts intracellularly to inhibit the multiplication of pathogenic bacteria after engulfment. It has a strong lytic effect on Gram-positive bacteria in particular and can be used as a preservative for foods such as sake, cheese, sausages, cream, raw pasta, aquatic products and ice cream.

In the USA, researchers have recommended the use of ε-mono-lysine as a preservative in food products. It has been found that ε-mono-lysine can interact with proteins or acidic polysaccharides in foods, resulting in a loss of antimicrobial capacity, and that ε-mono-lysine has a weak emulsifying ability. Therefore ε-mono-lysine is restricted to starchy foods.