Effects of rice starch-soy protein isolate interactions on the structural characteristics and digestive behaviors

Starch-protein complexes are regarded as an effective strategy in regulating the digestion behavior of starch. Nevertheless, the anti-digestive mechanisms of soy protein isolate (SPI) on the digestibility of rice starch (RS) remain unclear. This study aimed to investigate how the structural characteristics of RS-SPI complexes influence the adsorption of amylase on the gel surface and the internal mobility of amylase by comprehensively comparing the structural, morphologic, rheological and digestive properties of RS with RS-SPI complexes. Results showed that SPI interacted with RS by non-covalent (ionic bonds, hydrogen bonds, and hydrophobic interactions), and the gelatinization properties of RS were changed significantly by the addition of SPI. Besides, compared to RS, RS-SPI complexes had stranger V-type diffraction intensity, more compact gel network structure, larger particle sizes and weaker affinity with α-amylase, which were closely related to the anti-digestive properties of the complexes. Furthermore, RS-SPI complexes showed lower apparent viscosity and dynamic viscoelasticity than those of RS. With the increase of SPI content, in vitro digestion study confirmed that the content of resistant starch was increased from 3.57 % (RS) to 25.24 % (RS-40 %SPI) and the digestibility was decreased from 98.90 % (RS) to 77.91 % (RS-40 %SPI). Collectively, the present study unveiled the mechanisms of SPI on the digestibility of RS by hindering the binding of amylase to RS, which provided a valuable suggestion on the development of healthy foods with anti-digestive properties.