Unraveling microbial diversity and physicochemical hazard level in Thai traditional fermented shrimp paste (Kapi)

Fermented shrimp paste (Kapi) is a culturally significant condiment valued for its flavor and nutritional value. However, inconsistent production practices may lead to microbial contamination and histamine accumulation, posing health risks. Understanding microbial diversity, salt-tolerant pathogens, and the effectiveness of hygienic controls is essential for improving product safety and quality consistency. This study assessed the microbial and physicochemical characteristics of seven Kapi produced under varying hygienic conditions: a certified commercial export product (M1), a traditionally fermented product using 25% (w/w) salt (M2), wet-market bulk products (M3, M4), and sealed community-enterprise products (M5, M6, M7). Microbiological hazards were characterized using Oxford Nanopore sequencing, and physicochemical analyses, including histamine content, were conducted. M1 exhibited the highest safety and quality, with no detected pathogens. In contrast, M3 and M5 contained high microbial loads, including <i>Staphylococcus aureus</i>, <i>Bacillus cereus</i>, <i>Clostridium perfringens</i>, and fungi. Bacterial diversity varied significantly across samples, with M3 and M4 showing the greatest richness, whereas M6 had the lowest. Dominant species identified were <i>Lentibacillus salinarum</i>, <i>Lentibacillus amyloliquefaciens</i>, and <i>Lentibacillus kimchi</i> in M1, M3, and M4, and <i>Staphylococcus sciuri</i> in M2, M5, and M6, all of which possessed histamine-degrading potential. <i>Alkalibacterium kapii</i> dominated M7, while histamine-producing <i>Jeotgalicoccus halotolerans</i> was found in M5-M7. Physicochemical variations corresponded with production practices. M6 showed the highest histamine level (39.4 mg/kg), while M1 and M4 had the lowest (12.7 and 9.5 mg/kg, respectively), indicating differences in hygiene and salt management. Overall, microbial and physicochemical hazard levels were closely associated with production environments. To enhance the safety and consistency of Kapi, we propose a risk-based framework that includes standardizing salt concentration (25% w/w) to control microbial dynamics and histamine formation, strengthening hygienic practices from Good Hygiene Practice (GHP) to Good Manufacturing Practices (GMP) compliance to ensure adequate safety control, and applying defined starter cultures to stabilize fermentation and reduce variability. These strategies collectively address how hygiene, salt concentration, and environmental control influence microbial and physicochemical hazards in traditional fermented shrimp paste.