Stage-specific microbial dynamics and transmission pathways in salted seafood processing plants: A comparison of salted pollock roe and salted squid.

This study investigated microbial transmission dynamics and community structures across processing stages of two salted seafood products: salted pollock roe and salted squid. Samples of raw materials, environmental samples, and final products were collected from two processing plants (n = 87), and both culture-based analyses and 16S rRNA gene sequencing were performed. SourceTracker was used to track potential sources contributing to the final products. Microbial dynamics exhibited contrasting patterns between the two products due to differences in salting intensity and processing methods. In salted pollock roe, microbial counts decreased under high-salinity conditions, and the final microbial community was predominantly shaped by late-stage food-contact surfaces, particularly measuring containers. Conversely, salted squid exhibited increased microbial loads following the addition of seasoning ingredients (e.g., garlic and red pepper powder), which were identified as the primary contributors to the final microbial community. Despite these divergent transmission routes, marine-associated genera (Psychrobacter and Photobacterium) were commonly detected in both products. Taxonomically, salted pollock roe was enriched in environmental- and processing-associated bacteria, whereas salted squid was strongly enriched in lactic acid bacteria. Overall, these findings highlight stage-specific contributors to contamination and transmission patterns relevant to hygiene management. By integrating microbial loads with community-level source contributions, this study provides a basis for improving the quality and safety of salted seafood products.