Effect of Ultra-high Pressure Processing on Spoilage Microbial Flora of Oysters during Ice Storage and Lethal Function on Typical Strain Shewanella putrefaciens

In order to reveal the effect of ultra-high pressure processing(UHPP) on the spoilage bacteria flora of oysters and its mechanism, high throughput sequencing technology was applied to study the bacterial community structure in fresh and spoiled oysters. Survival rate, extracellular alkaline phosphatase (AKP) activity, extracellular reducing sugar content and electron microscope observation were used to discuss the lethal mechanism of UHPP on typical spoilage strain (Shewanella putrefaciens). The results showed that the microbial flora of fresh oysters were dominated by Vibrio, Shewanella and Pseudoalteromonas. However, the proportion of Vibrio decreased gradually during storage, and Shewanella and Pseudoalteromonas were dominant in spoiled oysters. UHPP changed the bacteria community of oysters, and Psychrobacter took an obvious advantage in spoiled oysters, the proportion of both Pseudoalteromonas and Shewanella was less than 1%. The survival rate of Shewanella putrefaciens had no significant changes at 100 MPa pressure treatments, then decreased rapidly with the increase of treatment pressure and no viable bacteria could be detected after 400 MPa processing. The extracellular alkaline phosphatase activity and reducing sugar content changed significantly under relative lower pressure treatment (<100 MPa), however the change magnitude became smaller along with the increase of processing pressure. UHHP caused cell adhesion and clustering. Along with the increasing of pressure, the boundaries of Shewanella putrefaciens cells became blurred, and eventually led to their death. © 2019, Editorial Office of Journal of CIFST. All right reserved.