Microbial Production and Industrial Applications of ( <i>S</i> )-Equol for Precision Health and Functional Food Innovation

Equol is a nonsteroidal, microbiota-derived estrogenic metabolite of the soy isoflavone daidzein, known for its potent antioxidant, anti-inflammatory, and selective estrogenic receptor modulating activities. With enhanced bioavailability and tissue-specific hormonal effects, equol has been proposed as a candidate for managing hormone-related conditions such as menopausal symptoms, prostate health, and metabolic inflammation. However, endogenous equol production is limited to 25-60% of individuals, depending on the presence of specific gut microbial consortia. This review highlights recent advances in equol research, emphasizing its molecular mechanisms of action, population-specific clinical evidence, and translational potential in functional foods and nutraceuticals. Particular attention is given to microbial production strategies, including native and engineered equol-producing strains from human, animal, and food origins, as well as emerging heterologous expression systems. We further discuss challenges and opportunities in scalable fermentation, formulation stability, and regulatory approval that are critical for the industrial application of equol in precision health solutions.