Effects of thermal treatment combined with multi-cycle high pressure processing on the bacterial diversity of mud snail (Bullacta exarata) during refrigerated storage

Thermal processing (TP) combined with multi-cycle high pressure processing (HPP) was explored to inactivate microbes in Bullacta exarata. Samples processed by TP with multi-cycle HPP were analyzed both by culture-dependent and -independent methods during refrigerated storage. Total microbial counts, psychrophilic bacteria counts, pH values, and conductivities were determined. TP and HPP processes resulted in higher pH and conductivity values, and also the conductivities of samples were significantly increased (P < 0.05) during refrigerated storage. The combined treatment significantly reduced total microbial counts by about 3 log CFU/g, and the surviving microbes grew slower during the storage period in treated sample. Samples treated with multi-cycle HPP30 (TP at 30 °C) had more surviving bacteria than samples treated with HPP60 (TP at 60 °C). The microbiota of B. exarata was composed mainly of Proteobacteria (40.59%), Firmicutes (36.43%) and Tenericutes (9.85%). Samples processed with HPP60 had the lowest bacterial diversity, and samples processed with HPP30 had the highest bacterial diversity. Bacterial diversity increased initially, and then decreased finally during refrigerated storage. These results demonstrated that HPP60 combined treatment is an effective method for food processing conditions.