Preservation mechanism of perilla in chilled oysters based on diversity analysis of protease-producing microbiota and proteolytic enzymes during spoilage

Abstract

This study investigated the physicochemical characteristics and bacterial spoilage of refrigerated oysters from five Chinese provinces, alongside evaluating perilla leaf extract (PLE) as a natural preservative. A total of 62 strains of protease-producing bacteria, predominantly Pseudoalteromonas, Shewanella, and regionally Vibrio, were identified across samples, with serine proteases and metalloproteases as the dominant secreted enzymes, accelerating oyster spoilage. Metagenomic analysis revealed that PLE treatment reduced bacterial diversity, shifting dominant genera from spoilage-associated Pseudoalteromonas and Shewanella to Pseudomonas and Marinomonas. PLE effectively inhibited protein degradation, maintaining higher protein content compared to the control, while lower amino acid nitrogen levels on the seventh day of refrigeration. Furthermore, PLE suppressed the growth of 53 isolated protease-producing strains at 24 h and inhibited their extracellular protease activity, particularly metalloproteases and serine proteases. These findings demonstrate that protease-producing bacteria and their enzymes critically contribute to oyster spoilage, while PLE serves as a sustainable preservative by mitigating microbial deterioration and protease-driven quality loss. The results highlight PLE's dual antimicrobial and protease-inhibiting properties, offering an eco-friendly strategy to enhance seafood shelf life and meet consumer demand for natural preservation solutions.