Beyond probiotics: Postbiotic compounds, intestinal health, and food technology perspectives in traditional Asian fermented soybean foods

Abstract

As the world grapples with rising cases of metabolic disorders, inflammatory bowel diseases, and immune-related disorders, gut health has become a pressing health and food technology issue. In this context, traditional fermented soybean products such as doenjang, natto, cheonggukjang, and tempeh in Asia are being reevaluated not only as sources of probiotics but also as providers of postbiotics, the non-viable microbial products and metabolites implicated in gut health. This PRISMA-guided narrative review examines the role of postbiotics produced in fermented soybean foods in maintaining gut microbiota balance, gut barrier function, and inflammation regulation, and explores their technological potential in functional food development. The study followed PRISMA 2020 guidelines, and the literature was searched through Scopus, PubMed, and Google Scholar from 2010 to 2025. Selected studies emphasized metabolic byproducts of Bacillus and Rhizopus species, their mucosal protective mechanisms, anti-inflammatory effects, and processing compatibility. Findings indicate that γ-PGA and SCFA exhibit barrier-regulating and immunomodulatory functions, while enzymes such as nattokinase and bacteriocins play roles in inhibiting pathogenic microorganisms and supporting microbial ecosystem balance. Due to their stability under refrigerated, acidic, and heat conditions, postbiotics are suitable for incorporation into functional foods and supplements. However, human clinical evidence remains limited, and future work should address dosage, standardization, and fermentation parameters. This review positions traditional fermented soybean foods as a promising platform for next-generation gut health functional foods, with relevant implications for food formulation and processing.