Incorporation of biovalorised okara in biscuits: Improvements of nutritional, antioxidant, physical, and sensory properties

Okara is the edible food waste resultant from soymilk processing, with limited utilisation due to its rapid putrefaction, poor digestibility, and undesirable sensorial properties. Okara fermentation with Rhizopus oligosporus and application into food product can improve these properties and promote consumption. Our study developed biovalorised okara biscuits and assessed their nutritional, physical, and sensorial properties. Control (no substitution), dried okara (OK), autoclaved okara (AOK), and fermented okara (RO) incorporated biscuits (20/40% flour substitution) were prepared. Total fibre increased with substitution, with a 2 ~ 3-fold increase in soluble fibre for RO compared to OK and AOK biscuits. Greatest isoflavones aglycones: glycosides ratio, total phenolic content, and antioxidant capacity were observed for RO biscuits. Regardless of okara type, greater substitution progressively lowered incremental area under curve of in vitro digestion glucose release. Substitution induced greater spreadability and darker colour. RO and control biscuits had similar hardness while OK and AOK biscuits were significantly harder. Okara biscuits yielded lower hedonic scores than control for overall flavour and liking despite good colour and surface appearance, warranting flavouring improvements. Conclusively, okara substitution enhanced biscuit nutritional quality. Biovalorised okara incorporation further improved the biscuit textural properties compared to AOK incorporation, with key nutritional enhancement on soluble fibre content and antioxidant capacity.