Phytochemical and nutritional modulation of adlay (Coix lacryma-jobi L.) by microbial fermentation

Adlay (Coix lacryma-jobi L.) is a nutrient-dense underutilized cereal rich in macronutrients, micronutrients, and diverse bioactive constituents, including polyphenols, flavonoids, coixan, and coixenolides. While these compounds exhibit potent antidiabetic, antioxidant, and anti-inflammatory activities, the nutritional quality of adlay is often compromised by antinutritional factors such as phytates and tannins. Microbial fermentation has emerged as a robust bioprocessing strategy to mitigate these antinutrients while concurrently enhancing the nutritional and functional profiles of adlay. This review focuses on biochemical transformations of nutritional, phytochemical, physicochemical, and sensory profiles during controlled fermentation. It further examines the strain-specific roles of lactic acid bacteria, Bacillus subtilis, Saccharomyces cerevisiae, Rhizopus oryzae, and Monascus purpureus in driving the synthesis of high-value secondary metabolites, such as γ-aminobutyric acid (GABA), tetramethylpyrazine (TMP), monacolin K, and bioactive peptides. The mechanisms underlying the enrichment of dominant bioactive compounds and their subsequent health effects in strain-specific bioconversion are discussed in detail. Finally, this review identifies current research gaps and proposes strategic directions to advance the development of fermented adlay as a premium functional food and nutraceutical substrate.