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 lype of spoilage is characterized by accumulation of gas and purge in the package wilh products having sour lo off odor. Although laclic acid bacteria as well as several nonlaclic acid bacteria are pre- dominant microflora in the fresh products, we isolated predominantly Leuconostoc camosum and Leuconostoc mesenteroides from the spoiled products. Many of these isolales produced bacteriocins lo which the predominanl gram-posilive bacteria normally found in these products are sensilive. As the leuconoslocs grew al low lemperalure and produce bacleriocins, they inhibiled growlh of associaled sensitive bacleria. Since they are helerofermenlalive, they produced CO₂ (resulting in accumulalion of gas in the package) and acids (resulting in reduclion in pH, accumulalion of purge (liquid), and sour and off-odor). The bacleriocinogenic isolales were sensilive lo 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.