Development of a depuration protocol for commercially important edible bivalve molluscs of India: Ensuring microbiological safety

Abstract

We investigated the effect of depuration of three naturally contaminated commercially important tropical edible bivalve molluscs by varying temperature, salinity and body-size of animals harvested from Ashtamudi and Vembanad estuaries, India using a static depuration system to ensure microbiological food safety. Before depuration, the levels of faecal indicators and pathogens were above the acceptable limits for live consumption. The depuration water temperature had a significant effect on bacterial elimination. Log reduction of faecal coliforms (FC) and E. coli varied between room-temperature (RTDS) and low-temperature depuration system (LTDS) and it was in the range of 1.39-2.44 and 1.88-2.82 log MPN, respectively under RTDS and LTDS. The elimination of bacterial pathogens such as Vibrio and Salmonella spp. was rapid in RTDS compared to LTDS. The highest elimination of FC and E. coli (2.39 and 2.92 log) was at 35 psμ depuration and the lowest (0.87 and 1.65 log) at 15 psμ depuration. The reduction of FC and E. coli was higher in the medium-sized animals compared to the small animals. Based on the results it is recommended that depuration using the static system under room-temperature (30 ± 1 °C); a salinity range of (25-35 psμ) and using medium-size bivalves (clam>30 mm; mussel >45 mm, and oyster >65 mm length) as optimum conditions for producing microbiologically safe bivalves for live consumption within 36 h.

Keywords: Ashtamudi and Vembanad Estuaries; Bacteria; Depuration; Edible Bivalves; Food safety.