Inactivation of vibrio parahaemolyticus in hard clams (mercanaria mercanaria) by high hydrostatic pressure (HHP) and the influence of HHP on the physical characteristics of hard clam meat
Vibrio parahaemolyticus bacterium is a leading cause of gastroenteritis associated with consumption of raw or undercooked molluscan shellfish in the US. The current post harvest treatment methods (relaying and depuration) used by the shellfish industry have been found to be ineffective in reducing naturally occurring Vibrio spp. and viral pathogens such as norovirus. The first objective of this research was to demonstrate the potential of HHP against Vibrio parahaemolyticus in littleneck New Jersey hard clams (Mercanaria mercanaria). The second objective was to identify and quantify the changes in appearance and texture of clam meat after HHP by instrumental analysis. Live clams were inoculated through bioaccumulation with approximately 8 log CFU/g of a cocktail culture of five outbreak strains of Vibrio parahaemolyticus. Inoculated clams were processed at pressures ranging from 250 to 450 MPa for hold times ranging between 2 to 6 minutes. The double layer plate method (DLPM) was used to recover pressure injured Vibrio parahaemolyticus cells. To study physical changes due to HHP, clams were exposed to pressures between 137 and 552 MPa. Volume, texture and color changes of clam meat were determined by instrumental measurements. Treatment conditions of 450 MPa and 6 minutes, 450 MPa and 4 minutes, 350 MPa and 6 minutes reduced the initial concentration of Vibrio parahaemolyticus to below the limit of detection. The volume of whole clam (processed in shell) also increased with negligible change in mass (together with shell), while drip loss reduced after HHP. The increase in volume may be due to the perfusion of clam liquor into the tissue rather than absorption of pressurizing medium (water). There was an increase in firmness of the clam meat at 276 MPa and a reduction at 552 MPa. However all HHP clams were found to be firmer compared to unprocessed clams. Lightness (L*) of the clam meat increased and redness (a*) decreased with increasing pressure. Although high pressure processed clams may pose a significantly lower risk from Vibrio parahaemolyticus, the effect of the accompanied physical changes on the consumer’s decision to purchase HHP clams remains to be determined.M.S.Includes bibliographical referencesby Gabriel Mootia
