Effects of storage on the microbial quality of slipper oysters, Crassostrea iredalei

Abstract

The effects of storage on the microbial quality of slipper oysters, Crassostrea iredalei, were examined. Oysters were stored at room temperature (24°C), under a blanket of ice (3-4 C), chilled (4-C) and frozen (-25°C) until they spoiled. The shelf life of oysters stored at room temperature was only two days. Oysters held under a blanket of ice had a shelf life of 14 days and chilled oysters, 22 days. Frozen oysters remained in good condition over the 64 day storage period. The initial total aerobic bacterial count of oysters was 10⁵cfu/g. Counts for frozen oysters decreased by 1 log (10⁴) while counts for oysters stored at other temperatures increased by 2-4 log (10⁷-10⁹). Bacterial typing of 50 randomly-picked colonies made every four days showed Pseudomonas to be the predominant spoilage organism. Total and fecal coliform counts did not increase even for oysters held at room temperature. Typical Staphylococcus aureaus colonies were isolated but were shown to be non-pathogenic by the coagulase test. Analyses for the presence of other organisms of public health concern revealed that Salmonella, Shigella, Vibrio cholerae, V. parahaemolyticus, Lactose + Vibrios (V. vulnificus) and fecal streptococci were present in very low or undetectable levels. Thus, hazards or risks associated with these organisms may be considered minimal.