The survival and recovery of Salmonella typhimurium phage type U285 in frozen meats and tryptone soya yeast extract broth

Abstract

The survival of S. typhimurium U285 was studied in cooked minced beef, sausage mixture and tryptone soya yeast extract (TSY) broth stored at freezer temperatures (−18°C to −20°C) for up to 10 weeks. Survival, as indicated by changes in viable counts, was best in minced beef followed by sausage mixture and TSY broth. Metabolic injury was minimal in each substrate whereas strucrural injury was detected, especially in TSY broth. Recovery, as indicated by changes in viable counts during thawing at room temperature, was generally complete after thawing 10 g or 10 ml amounts for 2 h. Viable counts obtained after thawing at refrigerator temperature for 24 h were similar to those obtained after 2h at room temperature. For specimens containing low inocula of salmonellae (0.5 cells/g), more isolations were obtained with pre-enrichment than with direct enrichment for minced beef and sausage mixture.