title: Effects of flash freezing, followed by frozen storage, on reducing Vibrio parahaemolyticus in Pacific raw oysters (Crassostrea gigas).
abstract: This study investigated the effects of flash freezing, followed by frozen storage, on reducing Vibrio parahaemolyticus in Pacific raw oysters. Raw Pacific oysters were inoculated with a five-strain cocktail of V. parahaemolyticus at a total level of approximately 3.5 x 10(5) most probable number (MPN) per gram. Inoculated oysters were subjected to an ultralow flash-freezing process (-95.5 degrees C for 12 min) and stored at -10, -20, and -30 degrees C for 6 months. Populations of V. parahaemolyticus in the oysters declined slightly by 0.22 log MPN/g after the freezing process. Subsequent storage of frozen oysters at - 10, -20, and -30 degrees C resulted in considerable reductions of V. parahaemolyticus in the oysters. Storing oysters at -10 degrees C was more effective in inactivating V. parahaemolyticus than was storage at -20 or -30 degrees C. Populations of V. parahaemolyticus in the oysters declined by 2.45, 1.71, and 1.45 log MPN/g after 1 month of storage at -10, -20, and -30 degrees C, respectively, and continued to decline during the storage. The levels of V. parahaemolyticus in oysters were reduced by 4.55, 4.13, and 2.53 log MPN/g after 6 months of storage at -10, -20, and -30 degrees C, respectively. Three process validations, each separated by 1 week and conducted according to the National Shellfish Sanitation Program's postharvest processing validation-verification interim guidance for Vibrio vulnificus and Vibrio parahaemolyticus, confirmed that a process of flash freezing, followed by storage at -21 +/- 2 degrees C for 5 months, was capable of achieving greater than 3.52-log (MPN/g) reductions of V. parahaemolyticus in half-shell Pacific oysters.
authors.affiliation: College of Food Science and Technology, Shanghai Ocean University, Shanghai, 200090, People's Republic of China.
authors.forename: Chengchu
authors.initials: C
authors.lastname: Liu
authors.forename: Jianzhang
authors.initials: J
authors.lastname: Lu
authors.forename: Yi-Cheng
authors.initials: YC
authors.lastname: Su
mesh_terms: D000818:Animals; D015169:Colony Count, Microbial / Q000379:methods; D003257:Consumer Product Safety; D049896:Crassostrea / Q000382:microbiology*; D005506:Food Contamination / Q000032:analysis / Q000517:prevention & control*; D005511:Food Handling / Q000379:methods*; D005519:Food Preservation / Q000379:methods; D005615:Freezing; D006801:Humans; D012758:Shellfish / Q000382:microbiology*; D013997:Time Factors; D014736:Vibrio parahaemolyticus / Q000254:growth & development*