Microbiological, chemical, and sensory assessment of Pacific oysters (Crassostrea gigas) stored at different temperatures

Abstract

The changes were studied in microbiological, chemical, and sensory properties of Pacific oysters stored at 10°C, 5°C, and 0°C. <I>Pseudomonas</I> (22%) and <I>Vibrionaceae</I> (20%) species were dominant in raw oysters. The dominant bacteria found in the spoiled samples were <I>Pseudomonas</I> regardless of the storage temperature. During storage, rapid increases in aerobic plate count (APC) values of the samples stored at 10°C and 5°C were observed, while no obvious lag phases were detected. With the samples stored at 0°C, a decrease in APC value during the first 4 days and a lag phase of about 6 days were observed. The APC values of the samples stored at 10°C, 5°C, and 0°C reached the level of 10⁷ CFU/g on day 6, 10, and 18, respectively. All the tested samples stored at different temperatures revealed a slight decrease in pH and a significant increase of total volatile basic nitrogen (TVB-N) during storage. The average TVB-N concentration of about 22.0 mg N/100 g was observed at the end of the shelf-life as determined by APC. Combined with the sensory assessments, the shelf-life of 6–7, 10–11, and 17–18 days for oysters stored at 10°C, 5°C, and 0°C, respectively, was determined.