Pressuring Oysters

January 12/Agriculture Business Week -- According to recent research from Cork, Ireland, "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 260MPa for three minutes or 400MPa for five minutes at 20C and stored at 0C either aerobically on ice, in vacuum packaging (VP) or under modified atmosphere packaging (MAP; 40% CO2, 60% N-2), compared with changes in untreated oysters."

"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 400MPa, 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," wrote M. Cruzromero and colleagues, University College.

The researchers concluded, "HP treatment, in combination with adequate chilled storage and MAP, can extend the shelflife and safety of oysters."

Cruzromero and colleagues published their study in the Journal of the Science of Food and Agriculture ("Influence of packaging strategy on microbiological and biochemical changes in high-pressure-treated oysters (Crassostrea gigas)". Journal of the Science of Food and Agriculture, 2008;88(15):2713-2723).

For additional information, contact J.P. Kerry, University College Cork, Dept. of Food & Nutrition Science, Cork, Ireland.

Publisher contact information for the Journal of the Science of Food and Agriculture is John Wiley & Sons Ltd., the Atrium, Southern Gate, Chichester PO19 8SQ, W Sussex, England.

From the January 19, 2009, Prepared Foods E-dition