The effects of various pressure treatments (OK, 30K, 60K, 75K psig) and packing medium (water or cocktail sauce) on shucked oysters were investigated. The pH, moisture content, microbiological tests (including aerobic plate count (APC) and anaerobic plate count (ANPC)), enzyme assays (i.e. α-amylase, β-amylase, lipase and peroxidase activities) were conducted to determine the quality of pressure treated oysters during a 6 week shelf-life study. The moisture content in water-packed oysters under OK, 30K, 60K and 75K psig pressure treatments was slightly increased during storage, while that in cocktail sauce-packed samples was significantly lower than in water-packed samples. Addition of cocktail sauce lowered the pH in oysters, which effectively inhibited the microbial growth, but altered the appearance. The microbial shelf-life of water-packed oysters with pressure treatment of 60K and 75K psig was extended several weeks compared with the controls while 30K psig had less of an effect. Pressure treatments did not inhibit enzyme activities in oysters, however, the addition of cocktail sauce was significant in inhibiting the enzyme activities in this study. / Graduation date: 2000