Mechanisms of rice protein hydrolysate regulating the in vitro digestibility of rice starch under extrusion treatment in terms of structure, physicochemical properties and interactions

The effect of protein hydrolysates on starch digestibility has been observed in other heat treatments but has yet to be extensively researched under extrusion. This study aimed to analyze the physicochemical properties, structure, and starch digestibility of extruded rice starch–protein hydrolysate (ERS–RPH) complexes prepared by extrusion treatment. The resistant starch contents of ERS–RPH (12.30 %–19.36 %) were higher than those of extruded starch alone (6.33 %). The interaction forces, physical barrier effects, and enzyme inhibition indicated that RPHs at varying hydrolysis degrees hindered starch digestibility by reducing its contact with enzyme and via adhesion and hydrogen bonding with starch. RPHs with higher hydrolysis exhibited greater inhibition of starch digestibility, limiting the swelling power of starch and the leaching of amylose, thereby improving the thermal stability of starch. Fourier transform infrared spectroscopy results revealed the presence of hydrogen bonding interactions between RPHs and starch in complexes, intensifying the ordered structure of starch. Extrusion caused an increase of 6.8 %–10.8 % in the relative crystallinity of ERS-RPH compared to extruded starch alone. Moreover, the strength of V-type structure was reinforced after extrusion. These results enhanced comprehension of how PRHs regulate starch digestibility under extrusion, and offer direction for producing slow-digesting foods.