Inactivation of microbial loads and retardation of quality loss in Asian hard clam (Meretrix lusoria) using high-hydrostatic-pressure processing during refrigerated storage

Abstract

The effects of high pressure processing (HPP) at 200, 300, 400, 500, and 600 MPa for 3 min on physicochemical quality and inactivation of microbial loads of Asian hard clam (Meretrix lusoria) were evaluated. In addition, the retardation effects in microbial growth and quality loss of pressurized hard clams stored at 4 °C were investigated. Results showed that the expanding rate, moisture content, shucking ratio, pH, L* (lightness), and W (whiteness) of clam meat increased significantly with the increase in pressure, but a* (redness) and b* (yellowness) values decreased. With the increase in pressure, the levels of aerobic plate count (APC), psychrotrophic bacteria count (PBC), coliform, and Vibrio parahaemolyticus in clam meat significantly decreased. Furthermore, HPP with a pressure of >400 MPa on clam samples significantly delayed the increase in APC (by 6–9 days within Taiwan's regulation standard limit) and PBC during storage at 4 °C. However, the samples pressurized more than 300 MPa had significantly lower levels of total volatile basic nitrogen (TVBN) than control samples during storage. Overall, the results indicated that pressurization at least 400 MPa for 3 min on Asian hard clam were able to reach the highest expanding rate and moisture content, and 100 % shucking, while it can reduce the coliform, and V. parahaemolyticus to a non-detectable level. In addition, HPP conditions of ≥400 MPa for 3 min significantly extended the shelf-life of hard clam during refrigerated storage. Therefore, HPP is a useful technique to preserve Asian hard clam meats due to its ability to reduce bacterial load and retard TVBN production.