Effect of Different Packaging Methods and Storage Temperatures on the Growth ofListeria monocytogenesin Raw and Hot Smoked Rainbow Trout (Oncorhynchus mykiss)

Abstract

The effect of packaging methods on the growth of Listeria monocytogenes (ATCC 19114, 7644, 19113) at 3°C and 7°C in fresh and hot smoked trout (Onchorynchus mykiss) were monitored for 30 d. Samples were packaged under an air, nitrogen, vacuum, or nitrogen gas flush with vacuum atmosphere. The strains of L. monocytogenes tested did not grow in raw trout at 3°C, but grew at 7°C from log 2 to 4 cfu/g after 10 days storage. The number of spoilage microbes increased substantially during storage at 7°C, causing changes in aroma that make the product unacceptable after 5 to 10 days. L. monocytogenes did not grow on hot smoked trout at 3°C, but increased to log 7 cfu/g at 7°C during storage. Aerobic microflora grew slowly at 3 and 7°C in the smoked trout, and sensory quality remained within an acceptable range under both temperature conditions. Because of the sensory changes associated with decomposition, consumers would most likely consider MAP packaged fresh trout, but not necessarily smoked trout, held at 7°C to be spoiled before L. monocytogenes levels would become high enough (e.g., 1,000 cfu/g or higher) to pose a food safety risk.