Impact of okara on quality and in vitro starch digestibility of noodles: The view based on physicochemical and structural properties

The development of cereal foods with slow starch digestibility is important for the general improvement of human health. In this study, the quality properties of noodles with added okara, in vitro starch digestibility, and the underlying mechanisms of the influence of okara on noodles were studied. Low concentrations (5 and 10 %) of okara improved the texture, cooking, and sensory properties of the noodles. Okara decreased the rapidly digestible starch (RDS) content, increased the resistant starch (RS) content, and reduced the predicted glycaemic index (pGI) of noodles. The pasting viscosity, thermal stability, and dynamic rheological results indicated that okara improved the starch crystallite stability of wheat flour and viscoelasticity of dough. Moreover, Fourier transform infrared (FTIR) spectroscopy showed that okara promoted the formation of starch-lipid complexes and improved the short-range structural order of starch. Additionally, microstructure imaging and protein network analysis (PNA) indicated that low addition of okara promoted the compactness of the okara-gluten-starch matrix, thus reducing the contact between starch and hydrolytic enzymes. These results reveal the effect of okara on the quality properties and starch digestibility in a starch-gluten complex system.