Abstract
During harvesting and storage, microbial pathogens and natural spoilage flora may grow, negatively affecting the composition and texture of oysters and posing a potential health threat to susceptible consumers. A solution to these problems would mitigate associated damaging effects on the seafood industry. The purpose of this study was to investigate the effects of storage temperature on growth of vibrios as well as other microbial, sensory, and textural characteristics of post-harvest shellstock Eastern oysters (Crassostrea virginica). Oysters harvested from the Chesapeake Bay, Maryland, during summer months (June, July, and August, 2010) were subjected to three storage temperatures (5, 10, and 20°C) over a 10-day period. At selected time intervals (0, 1, 3, 7, and 10 days), two separate samples of six oysters each were homogenated and analyzed for pH, halophilic plate counts (HPC), total vibrios, and Vibrio parahaemolyticus (Vp). Oyster meats shucked after storage were also organoleptically evaluated (acceptability, appearance, and odor). Texture analysis was performed using a texture analyzer on meats shucked from oysters held under the same conditions. The pH of the oyster homogenates showed no consistent pattern with storage time and temperature. The HPC (4.5–9.4 log CFU/g) were highest on day 7 at 20°C while olfactory acceptance reduced with time and increasing storage temperatures. The Vp counts increased over time from 3.5 to 7.5 log MPN/g by day 10. Loss of freshness as judged by appearance and odor was significant over time (p < 0.05). Toughness of oysters increased with storage time at 5 and 10°C from days 1 to 3 but was inconsistent after day 7. The results indicate that the length of storage and temperature had a significant effect on bacterial counts and olfactory acceptance of oysters but had an inconsistent effect on texture.
Highlights
The Eastern oyster (Crassostrea virginica), commonly found in the intertidal zones of the eastern United States, has been traditionally harvested as a food source for thousands of years (1)
HALOPHILIC PLATE COUNTS Halophilic plate counts of oysters were highest on day 7 at 20°C and on day 10 at 5 and 10°C during storage, with a log range of about 4.5–9.4 log CFU/g (Figure 1)
Oysters were harvested from the Chesapeake Bay during the warmer months and stored over a range of temperatures to be representative of industry and consumer practices
Summary
The Eastern oyster (Crassostrea virginica), commonly found in the intertidal zones of the eastern United States, has been traditionally harvested as a food source for thousands of years (1). Among the Gram-negative rods, Vibrio parahaemolyticus (Vp) is economically important because of its virulence This halophilic bacterium (Family: Vibrionaceae) is commonly abundant in the estuarine waters worldwide and causes gastroenteritis in humans (7, 8). Human transmission of this pathogen is mainly through the consumption of raw, poorly cooked, or mishandled seafood including oysters. These reports further indicated that Vp numbers in oysters and water increase with warmer temperatures (5, 9, 10). Vp can grow over a broad pH range (4.8–11.0), the optimal range is pH 7.6–8.6 (8, 11)
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