Valorization of okara (soybean residue) for the sustainable production of value-added products

The large-scale production of tofu and soymilk generates substantial quantities of okara. Okara is a fiber (50%), protein (20–30%), lipid (6.22–21.98%), and bioactive rich soybean by-product that is often underutilized and discarded due to its high moisture content (70–80%) and rapid spoilage. However, recent advancements in food science and biotechnology have transformed okara from agro-industrial waste into a promising raw material for functional food applications. This review comprehensively examines the physical, nutritional, and bioactive attributes of okara, emphasizing its potential as a sustainable resource for value-added product development. Various valorization strategies, including physical, chemical, and particularly microbial fermentation techniques, are explored for enhancing the functional and sensory qualities of okara-derived products. Their drawbacks and challenges are also covered. Special attention is given to the role of microbial fermentation, notably by bacteria and fungi, in improving the bioavailability of okara’s health-promoting compounds. The functional food applications of fermented okara, including its anti-diabetic, anti-obesity, anti-hyperlipidemic, and antioxidant properties, are critically discussed with supporting scientific evidence. Despite significant progress at laboratory scale, challenges remain in scaling up bioprocessing systems and ensuring product consistency. Future research directions should focus on optimizing fermentation parameters and utilizing multi-strain microbial consortia to fully harness the nutritional and therapeutic potential of okara. By bridging current research gaps, okara can be successfully valorized into a range of economically viable, health-enhancing food ingredients, contributing to waste reduction and the promotion of a circular bioeconomy.