Nisin, also known as lactochainin or nisaplin, is a polypeptide compound extracted from the fermentation products of lactic acid streptococcus (Streptococcus lactis). It is currently the only bacteriocin approved for use as a food preservative. The unique properties and broad spectrum of antibacterial activity of nisin have made it an important addition to the food industry, ensuring food safety and extending shelf life. This article delves into the application of nisin in food additives, exploring its characteristics, antibacterial mechanism, and various uses in different food categories.
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Characteristics and Antibacterial Mechanism of Nisin
Nisin is a natural food preservative with high activity, non-toxicity, safety, and no side effects. After ingestion, it is rapidly hydrolyzed into amino acids under the physiological pH conditions and α-chymotrypsin action in the human body. This process does not alter the normal flora in the human intestinal tract or cause antibiotic resistance issues, nor does it exhibit cross-resistance with other antibiotics.
The antibacterial mechanism of nisin primarily involves disrupting the cell membrane of sensitive Gram-positive bacteria. Early research showed that after nisin acts on vegetative cells, cellular substances rapidly leak out, including ATP and other ions, accompanied by a complete loss of membrane potential. If the cell membrane is severely affected, complete cell lysis may occur. Gram-negative bacteria are resistant to nisin, but treatments or reagents that increase cell wall permeability can greatly enhance their sensitivity to nisin.
History of Nisin's Application in Food Preservation
The use of nisin in food preservation has a long history. In 1928, Rogers noticed that the metabolites of lactic acid streptococcus could inhibit the growth of other lactic acid bacteria. In 1951, Hirsch et al. successfully used nisin to inhibit the spoilage of cheese caused by clostridium gas-producing bacteria, thereby improving cheese quality. In 1953, the British companies Aplin and Barrett first sold this new preservative as a commercial product.
In 1969, the Joint Expert Committee on Food Additives (JECFA) of the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) approved nisin as a food preservative for use in the food industry. In 1988, the U.S. Food and Drug Administration (FDA) also formally approved the use of nisin in food. Since then, nisin has been widely used in various countries around the world.
Applications of Nisin in Different Food Categories
Meat Products
Nisin is effective in inhibiting many Gram-positive bacteria that cause food spoilage, such as Lactobacillus, Leuconostoc, Micrococcus, Staphylococcus, Listeria, and Streptococcus. It has a particularly strong inhibitory effect on spores, such as Bacillus and Clostridium. For example, adding 0.03-0.05g/kg of nisin to fresh milk can inhibit the germination and reproduction of Bacillus and Clostridium spores.
In meat products such as roast meat, ham, sandwiches, sausages, and Frankfurt sausages, nisin can inhibit most Gram-positive bacteria without affecting the product's color, aroma, and taste. It can also reduce the use of nitrate or nitrite and improve product quality and shelf life.
Dairy Products
Nisin is widely used in dairy products, including yogurt, milk beverages, liquid eggs, and egg products. Adding 0.05g/kg of nisin to yogurt with a pH of about 4 can extend the shelf life of the product from 6 days at room temperature to more than a month after sterilization at 90°C for 20 minutes.
In canned milk subjected to ultra-high temperature sterilization and aseptic filling, adding 0.05g/kg of nisin can reduce the product spoilage rate from 0.04%.
Canned Foods
Canned foods are often contaminated with highly heat-resistant bacterial spores, such as thermophilic bacillus and thermosaccharolytic clostridium. These spores can grow under suitable conditions, causing gas and acid production, leading to spoilage. Adding 0.1g/kg of nisin to canned foods can allow the products to be stored under hot conditions for up to 2 years, reducing heat treatment intensity by half, saving energy, and maintaining the nutritional value, appearance, flavor, color, and quality of the canned foods.
Seafood Products
Seafood products such as fish and shrimp are prone to spoilage and contamination by bacteria such as Listeria and Clostridium botulinum due to their high moisture content and cold consumption habits. Adding 0.1-0.15g/kg of nisin can inhibit the growth and reproduction of spoilage bacteria, extending the freshness and shelf life of the products.
Baked Goods and Convenience Foods
Nisin can also be used in baked goods, convenience foods, and seasonings. It can replace or partially replace chemical preservatives and coloring agents (such as nitrite) to meet the needs of producing health foods and green foods.
Beverages and Fruit Juices
Nisin can be added to beverages and fruit juices to extend their shelf life. For example, adding a certain amount of nisin to beverages can inhibit the growth of microorganisms and maintain the clarity and flavor of the beverages.
Safety and Toxicity of Nisin
Nisin's safety as a food additive has been extensively researched and verified over decades.
Firstly, Nisin is composed of 34 amino acid residues and has a molecular weight of approximately 3500 Da. It is widely used in the food industry due to its ability to inhibit most Gram-positive bacteria and spores of Bacillus species. Importantly, after consumption, Nisin is quickly hydrolyzed into amino acids under the physiological pH conditions of the human body and the action of α-chymotrypsin, without altering the normal flora in the human intestinal tract or causing antibiotic resistance issues.
Secondly, Nisin has been recognized as a safe food preservative by various international organizations. The Joint Expert Committee on Food Additives (JECFA) of the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) confirmed its safety in 1969. The U.S. Food and Drug Administration (FDA) also approved its use in food in 1988. China's Ministry of Health similarly approved its use as a food preservative in 1992.
Furthermore, extensive toxicological studies have shown that Nisin is non-toxic and has no adverse effects on the human body. It is easily digested and absorbed by the human body and does not accumulate in tissues or cause harm to the body. The lethal dose 50% (LD50) values for rats are relatively high, indicating low toxicity.
Conclusion
In summary, nisin, as a natural food preservative, has broad application prospects in the food industry due to its high antibacterial activity, non-toxicity, safety, and no side effects. It can effectively inhibit the growth and reproduction of spoilage bacteria, extend the shelf life of food, and maintain the quality and safety of food. With the continuous progress of extraction technology and the increasing demand for food safety, the application of nisin in the food industry will become more widespread and in-depth.