Influence of packaging strategy on microbiological and biochemical changes in high-pressure-treated oysters (Crassostrea gigas)

BACKGROUND: High-pressure (HP) treatment is being increasingly employed for commercial processing of oysters, but there is relatively limited information on the microbiological quality and enzymatic activity of HP-treated in-shell oysters. The objective of this research was to study the influence of packaging strategy on microbiological and biochemical changes in oysters HP treated at 260 MPa for 3 min or 400 MPa for 5min at 20°C and stored at 0°C either aerobically on ice, in vacuum packaging (VP) or under modified atmosphere packaging (MAP; 40% CO₂, 60% N₂), compared with changes in untreated oysters. RESULTS: Both HP treatments reduced the microbiological load to below the detection limit (<100 colony-forming units g^-1). MAP and VP also delayed subsequent microbial growth compared with aerobically stored samples. After 21 days of storage, total volatile base levels remained lower than the proposed acceptability limits for all samples; however, after 28 days, only oysters HP treated at 400 MPa, irrespective of the packaging system used, did not exceed this limit. HP increased the thiobarbituric acid-reactive substance (TBARS) values of oysters, indicating increased lipid oxidation. During storage, TBARS values of all MAP and VP oysters remained lower than those of aerobically stored oysters. CONCLUSION: HP treatment, in combination with adequate chilled storage and MAP, can extend the shelf-life and safety of oysters.