Effect of trisodium phosphate on Listeria monocytogenes attached to rainbow trout (Oncorhynchus mykiss) and shrimp (Penaeus spp.) during refrigerated storage

The potential of using trisodium phosphate (TSP) to reduce bacterial populations in fresh fishery products was explored since TSP has recently been approved by USDA for its usage in poultry processing to eliminate Salmonella contamination. Fresh headed shrimp and rainbow trout fillets were inoculated with L. monocytogenes before dipped in tap water, 10% TSP, or 20% TSP solutions and overwrap-packaged. Surface pH values, psychrotrophic plate counts, and L. monocytogenes counts of inoculated shrimp and trout fillets were determined after 0, 3, 6, and 9 days of storage at 4C. The TSP treatment resulted in relatively high residual surface pH values (11-12) initially in both shrimp and trout fillets. Compared to tap water dipping, TSP treatment did not significantly reduce psychrotrophic or Listeria populations in shrimp. However, the 20% TSP treatment significantly (p<0.05) lowered 0-day psychrotrophic and L. monocytogenes counts of trout fillets and remained effective for 6 days during storage at 4C.