Changes in the microbiological and physicochemical quality of high-pressure-treated oysters (Crassostrea gigas) during chilled storage

Changes in the physicochemical and microbiological quality of oysters HP-treated at 260, 400 or 600 MPa for 5 min and stored at 2 degrees C on ice for 31 days were investigated. Microbial counts after HP treatment showed that the bacterial load was initially reduced at all pressures to levels below the detection limit. HP-treated oysters showed significantly increased pH and lightness (P < 0.05) relative to untreated oysters; during storage, pH changed little in the pressurised oysters but decreased slightly in untreated oysters. Little changes in colour were observed during storage at 2 degrees C on ice, compared to untreated oysters, which showed increased b-values (stronger yellow colour). From tests of mechanical properties, HP-treated oysters showed significantly increased cutting strength (P < 0.05) with increasing treatment pressure compared to controls throughout storage. However, HP increased lipid oxidation, the rate of which was dependent on the pressure applied. This study confirmed that HP processing can inactivate microorganisms and delay microbial growth in chilled stored oysters, but also affects their quality attributes. (C) 2007 Elsevier Ltd. All rights reserved.