Synergistic Effect of Biopreservation and Vacuum Packaging on the Control of Listeria monocytogenes in Raw Tuna Steaks.

Abstract- In the present study, Nisin, a bacteriocin produced Lactococcus lactis subsp. lactis, was used as a biopreservative agent against L. monocytogenes in raw Tuna steaks under chilled conditions. In vitro antimicrobial activity and MIC of nisin against L. monocytogenes (ATCC 19111) were determined prior to the application of the 6 different experimental treatments on Yellowfin Tuna (Thunnus albacares) steaks. The treated samples were stored at a chilled temperature (3 ± 0.3 ̊̊ C) for 16 days with the microbiological and biochemical quality assessment done on day 0, 2, 4, 8, 12, 16 and day 0, 4, 8, 12, 16 respectively. While microbiological quality was assessed by determining the total plate count and by enumerating L. monocytogenes, biochemical quality assessment was done by determining TVB-N, TMA-N, pH, PV and FFA for the treated samples.

While TPC showed an increase for samples subjected to all the treatments throughout the storage period, L. monocytogenes count exhibited an initial decrease followed by an increase for samples subjected to all the treatments. For TVB-N, the lowest value at the end of storage was found under a combined effect of vacuum packaging and 1000 IU/ml of nisin. pH of the samples subjected to all the treatments remained within the range 5.49- 5.98 throughout the study. TMA-N, PV and FFA were not found to be good indicators of spoilage in the present study.

It was concluded that the best effect, in terms of both, the control of general microbiota as well as TVB-N formation in raw Tuna steaks, is obtained by a combination of vacuum packaging and 1000 IU/ml of nisin. In terms of reductionin L. monocytogenes count, the most effective treatment is vacuum packaging combined with 2000 IU/ml of nisin. The synergism of vacuum packaging eith 2000 IU/ml of nisin exerted the best effect on both, microbiological and biochemical quality of raw Tuna steaks at chilled (3 ± 0.3 ̊ C) storage.