Survival of Salmonella spp. and Escherichia coli O157 : H7 on fresh and frozen strawberries

For maximum shelf life, fresh strawberries are harvested directly without w ashing into retail containers. Frozen berries are usually hulled in the fie ld and washed prior to freezing, sometimes with the addition of sucrose. To determine survival of potential bacterial contaminants, cut or intact surf aces of fresh strawberries were spot inoculated with five- or six-strain co cktails of Salmonella or Escherichia coli O157:H7 (log 7.0 CFU/sample). Ino culated strawberries were dried for 1 h at 24 degreesC and were stored in c losed containers at 5 or 24 degreesC. Sliced strawberries with or without a dded 20% sucrose were inoculated with one of two strains of E. coli O157:H7 and frozen at -20 degreesC. An initial population reduction of approximate ly 0.5-log cycles was observed on intact but not cut berries after the 1-h drying period. During storage at 24 degreesC for up to 48 h, populations of Salmonella and E. coli O157:H7 did not decline further. When strawberries were stored at 5 degreesC for up to 7 days, populations of both pathogens r emained constant on cut surfaces but decreased by 1- to 2-log cycles on int act surfaces. After 30 days of frozen storage, the population of E. coli O1 57:H7 had declined by 0.7- to 2.2-log cycles (with and without sucrose, res pectively). Results of this study indicate that E. coli O157:H7 and Salmone lla are capable of survival but not growth on the surface of fresh strawber ries throughout the expected shelf life of the fruit and can survive in fro zen strawberries for periods of greater than 1 month.