What is Nisin?
Nisin is a natural antimicrobial agent used as a preservative in heat processed and low pH foods. The nisin preparation is a concentrate of dry material derived from the controlled fermentation of a naturally occurring Streptococcus lactis. This bacterium contains nisin, a group of related peptides (partial amino acid chains that make up proteins) with antibiotic activity. The chemical nisin cannot be synthesized artificially, so the nisin-producing bacteria are basically farmed for their synthesis of nisin.
How is it made?
Technical specifications for  nisin  indicate that the process begins by fermenting the milk bacteria. The resulting nisin is concentrated, separated, and dried before milling into fine particles and standardized by the addition of sodium chloride (salt). The resulting typical composition is nisin (2.5%), sodium chloride (greater than 50%) , protein (23.8%), and moisture (less than 3%).
Is it safe?
Nisin is listed as a "natural preservative" in chemical dictionaries. In addition,  nisin as "replacement or partial replacement of chemical preservatives." Nisin was awarded the Generally Regarded as Safe (GRAS) designation in the U.S. Federal Register of April, 1988 and is approved as a natural food preservative in the United States. It is also approved as a natural food preservative by more than 60 other countries as well as with the Food and Agriculture Organization/World Health Organization and the European Union. The Nisaplin brand of nisin is certified kosher, as well.
Use and limitations:
In the U.S., nisin is used to inhibit outgrowth of Clostridium botulinum spores (the cause of botulism) and toxin formation in pasteurized process cheese spreads with fruits, vegetables or meats at levels not exceeding good manufacturing practice. Current good manufacturing practice in this case is the quantity of the ingredient that delivers a maximum of 250 p.p.m. of nisin in the finished product.  nisin is also approved for liquid egg products, dressings, and sauces. In other countries it is also used in fresh and recombined milk, fermented beverages like beer, canned foods, frozen desserts, and high moisture/reduced fat foods.
Nisin is considered effective at controlling a wide range of gram-positive organisms including: Listeria, enterococcus, Bacillus sporothermodurans, and clostridium. Used alone, it is not effective on gram-negative bacteria (like E coli ), yeasts, and molds. However, research suggests that it may be useful against some gram-negative bacteria when used in conjunction with other preservatives.
In conclusion-based on the way it is manufactured, its GRAS status, and its "natural" labeling designation-nisin appears to qualify as a safe and natural food preservative.

The difference between Nisin A and Nisin Z

Two natural nisin molecules exist, termed nisin A and nisin Z. The structure of the nisin A molecule was elucidated in 1971. It is a 34-amino-acid polypeptide with amino and carboxyl endgroups, and five internal ring structures involving disulfide bridges. It possesses three unusual amino acids: dehydroalanine, lanthionine, and β-methyllanthionine. Lanthionine appears to be a common feature in a number of more recently characterized bacteriocins that are collectively known as lantibiotics. Nisin Z differs from nisin A by the substitution of asparagine for histidine at position 27. Nisin Z has a similar antimicrobial activity to nisin A, although nisin Z shows greater diffusion in agar gels. Nisin A has a molecular weight of 3354 Da. There is evidence that nisin can exist as both dimers and tetramers.

Nisin applied to Alcoholic Beverages J. Delves-Broughton, in Encyclopedia of Food Microbiology (Second Edition, 2014

Nisin has a potential role in the production of alcoholic beverages. It has been demonstrated that nisin is effective in controlling spoilage by lactic acid bacteria, such as Lactobacillus, Pediococcus, Leuconostoc, and Oenococcus at a level of 0.25–2.5 mg l?1 in both beer and wine. Yeasts are completely unaffected by nisin, which allows its addition during the fermentation. Identified applications of nisin in the brewing and wine industry include: its addition to fermenters to prevent or control contamination, increasing the shelf life of unpasteurized beers, reducing pasteurization regimes, and washing pitching yeast to eliminate contaminating bacteria (as an alternative method to acid washing, which affects yeast viability). Formerly, nisin could not be used during wine fermentations that depend on malolactic acid fermentation. However, this problem has been overcome by developing nisin-resistant strains of Oenococcus oenos, which can grow and maintain malolactic fermentation in the presence of nisin. In the production of fruit brandies, the addition of nisin reduces the growth of competitive lactic acid bacteria and directly favors the growth of the fermenting yeast, to increase alcohol content by at least 10%.

Potential in Food Preservation

Dairy Products
Nisin is used in pasteurized, processed cheese products to prevent outgrowth of spores such as those of Clostridium tyrobutyricum that may survive heat treatments as high as 85–105°C. Use of nisin allows these products to be formulated with high moisture levels and low NaCl and phosphate contents, and also allows them to be stored outside chill cabinets without risk of spoilage. The level of nisin used depends on food composition, likely spore load, required shelf life and temperatures likely to be encountered during storage.
Nisin is also used to extend the shelf life of dairy desserts which cannot be fully sterilized without damaging appearance, taste or texture. Nisin can significantly increase the limited shelf life of such pasteurized products.
Nisin is added to milk in the Middle East where shelf-life problems occur owing to the warm climate, the necessity to transport milk over long distances and poor refrigeration facilities. It can double the shelf life at chilled, ambient and elevated temperatures and prevent outgrowth of thermophilic heat-resistant spores that can survive pasteurization. It can also be used in canned evaporated milk.

Food Packaging with Antimicrobial Properties

M. Mastromatteo, ... M.A. Del Nobile, in Encyclopedia of Food Microbiology (Second Edition), 2014

Direct Incorporation of Bacteriocins into/onto the Polymeric Film
Nisin received considerable attention in the food packaging sector, being the sole purified antimicrobial peptide approved by the US Food and Drug Administration. Nisin was incorporated into a polyethylene-based plastic film that was used to vacuum-package beef carcasses. Nisin retained activity against Lactobacillus helveticus and Brochothrix thermosphacta inoculated in carcass surface tissue sections. Nisin was also incorporated in films made up of hydroxy-propyl-methyl-cellulose. Inhibitory effect has been demonstrated against L. innocua and St. aureus, but film additives such as stearic acid, used to improve the water vapor barrier properties of the film, significantly reduced the inhibitory activity. Nisin, lauric acid, and ethylenediamine tetraacetic acid (EDTA) were included in corn zein films and then exposed to broth cultures of Salmonella enteritidis. None of the combinations produced reductions of the pathogen greater than 1 log CFU ml?1. In contrast, the use of edible films with nisin, EDTA, citric acid, and Tween 80 was evaluated on Salmonella typhimurium in poultry skin. Nisin is inactive against yeast, molds, and Gram-negative bacteria. This partial success of nisin as a natural food preservative has prompted examination of other bacteriocins. Bacteriocins in general should not be used as the main processing step to prevent the growth or survival of pathogens but to provide an additional hurdle to reduce the likelihood of foodborne disease. The combination of antimicrobials with other inhibitory treatments such as high hydrostatic pressure treatment has been proposed to achieve a high inactivation of Gram-negative foodborne pathogens. Natamycin is commonly used as an antifungal agent for cheese and sausages. Natamycin-impregnated cellulose films showed inhibitory effect against P. roquefortii on Gorgonzola cheese. Combination of nisin and natamycin in cellulose film prolonged the shelf life of sliced mozzarella cheese by 6 days. In contrast, methyl-cellulose and wheat gluten films containing natamycin did not cause any significant decrease of P. roquefortii on cheese surface. The bilayer coating of chitosan and polyethylene wax microemulsion, including natamycin, demonstrated an inhibitory effect against two pathogenic fungi during storage of melon.

 

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