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Biopreservation refers to extended storage life and enhanced safety of foods using the natural microflora and (or) their antibacterial products. Lactic acid bacteria have a major potential for use in biopreservation because they are safe to consume and during storage they naturally dominate the microflora of many foods. In milk, brined vegetables, many cereal products and meats with added carbohydrate, the growth of lactic acid bacteria produces a new food product. In raw meats and fish that are chill stored under vacuum or in an environment with elevated carbon dioxide concentration, the lactic acid bacteria become the dominant population and preserve the meat with a "hidden' fermentation. The same applies to processed meats provided that the lactic acid bacteria survive the heat treatment or they are inoculated onto the product after heat treatment. This paper reviews the current status and potential for controlled biopreservation of foods.

Leucocin A-UAL 187 is a bacteriocin produced by Leuconostoc gelidum UAL 187, a lactic acid bacterium isolated from vacuum-packaged meat. The bacteriocin was purified by ammonium sulfate or acid (pH 2.5) precipitation, hydrophobic interaction chromatography, gel filtration, and reversed-phase high-performance liquid chromatography with a yield of 58% of the original activity. Leucocin A is stable at low pH and heat resistant, and the activity of the pure form is enhanced by the addition of bovine serum albumin. It is inactivated by a range of proteolytic enzymes. The molecular weight was determined by mass spectrometry to be 3,930.3 0.4. Leucocin A-UAL 187 contains 37 amino acids with a calculated molecular weight of 3,932.3. A mixed oligonucleotide (24-mer) homologous to the sequence of the already known N terminus of the bacteriocin hybridized to a 2.9-kb HpaII fragment of a 7.6-MDa plasmid from the producer strain. The fragment was cloned into pUC118 and then subcloned into a lactococcal shuttle vector, pNZ19. DNA sequencing revealed an operon consisting of a putative upstream promoter, a downstream terminator, and two open reading frames flanked by a putative upstream promoter and a downstream terminator. The first open reading frame downstream of the promoter contains 61 amino acids and is identified as the leucocin structural gene, consisting of a 37-amino-acid bacteriocin and a 24-residue N-terminal extension. No phenotypic expression of the bacteriocin was evident in several lactic acid bacteria that were electrotransformed with pNZ19 containing the 2.9-kb cloned fragment of the leucocin A plasmid.Bacteriocins are antimicrobial peptides or proteins formed by bacteria. The potential applications for bacteriocin-producing lactic acid bacteria in food preservation has stimulated interest in the characterization of these substances. However, maintaining activity during isolation and purification has proved difficult, and the full or partial amino acid sequences of only five such bacteriocins have been reported. The most extensively studied is nisin A (2, 3, 7, 34), a posttranslationally modified bacteriocin from Lactococcus lactis subsp. lactis. Nisin has been approved for use as a preservative in foods in over 45 countries (9). It is ribosomally synthesized (6, 10) and is one of a group of lantibiotics that possess lanthionine-or methyllanthionine-containing rings resulting from the attack of cysteine sulfhydryl groups on dehydroalanine or dehydrobutyrine residues (derived from serine or threonine). Partial characterization of lactacin 481 from L. lactis shows that it also contains lanthionine rings, but the full sequence has not yet been published (31). In contrast, lactocin S from Lactobacillus sake (27)