PREVALENCE AND BIOLOGICAL-CONTROL OF BACTERIOCIN-PRODUCING PSYCHROTROPHIC LEUCONOSTOCS ASSOCIATED WITH SPOILAGE OF VACUUM-PACKAGED PROCESSED MEATS

Low heat-processed vacuum-packaged commercial meat products are expected to have a relatively long shelf life at refrigerated temperature. However, temperature abuse often occurs and spoilage of these products is not uncommon. One common type of spoilage is characterized by accumulation of gas and purge in the package with products having sour to off odor. Although lactic acid bacteria as well as several nonlactic acid bacteria are predominant microflora in the fresh products, we isolated predominantly Leuconostoc carnosum and Leuconostoc mesenteroides from the spoiled products. Many of these isolates produced bacteriocins to which the predominant gram-positive bacteria normally found in these products are sensitive. As the leuconostocs grew at low temperature and produce bacteriocins, they inhibited growth of associated sensitive bacteria. Since they are heterofermentative, they produced CO2 (resulting in accumulation of gas in the package) and acids (resulting in reduction in pH, accumulation of purge (liquid), and sour and off-odor). The bacteriocinogenic isolates were sensitive to nisin or a bacteriocin (probably nisin) produced by Lactococcus UW1. An approach in which either nisin or a similar bacteriocin was added to the product formulation could be effective to control growth of the leuconostocs in the products. Alternately, a low level of homofermentative lactic acid bacteria, that can produce nisin or similar bacteriocin at low temperature (such as Lactococcus UW1) could be incorporated in the package to control heterofermentative leuconostocs associated with spoilage of the meat products.