Survival of Vibrio parahaemolyticus in Korean-style salted oysters Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/wm117s50j

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  • This study was designed to determine the survival of Vibrio parahaemolyticus in salted oysters as prepared in Korea. Three levels of salt concentration were included; 3.0%, 6.8%, and 10.6% of the weight of the raw oysters. Two methods were used to inoculate the products, surface-inoculation and injection into the oysters, which were then held at 18°C. Multiplication of V. parahaemolyticus (Japanese strain T-3765-1) did not occur in the salted oysters, except for a slight increase in numbers after 24 hours from surface-inoculated samples with 3.0% salt and all samples of injected oysters. The samples with the higher salt concentrations showed longer survival of the organisms. Numbers of survivors in surface-inoculated oysters were markedly reduced within three days; the samples of injected oysters did not show reduced numbers in this period. There were more survivors from the injected samples over the storage period than from the surface-inoculated samples. No viable cells were observed after seven days from the surface-inoculated samples with 3.0% salt and the injected samples with 3.0% salt, after eight days from the surface-inoculated samples with 6.8% salt, after nine days from the injected samples with 6.8% salt, and after 11 days from the injected samples with 10.6% salt. A small number of V. parahaemolyticus were recovered from the surface-inoculated samples with 10.6% salt after eight days, the last testing period for these samples. The results of pH measurement suggested that the samples with higher salt concentration may have prolonged survival of V. parahaemolyticus through the effect of the higher pH value. An analysis of variance revealed a significant difference (5% level) in recovery between a modified isolation medium (Twedt and Novelli) and thiosulfate-citrate-bile salts-sucrose agar. Salt concentrations of 3.0%, 6.8%, and 10.6% slightly reduced the total bacterial counts after three days from the two lots of oysters used for the surfaceinoculated samples and further reduction was observed after seven days; reduction in numbers was not detected within 8 or 11 days from the two lots used for the injected samples. The latter two lots had much lower plate counts at the beginning of the experiment. No relationship was found between pH and total bacterial counts on the salted oysters.
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