Synergistic effects of pullulanase and α-amylase on starch-glyceryl monostearate interactions and digestibility in extruded rice flour

Abstract

Amylose produced by hydrolysis of the α-1,6 glycosidic bond in starch by pullulanase can form antidigestive V-type complexes with lipids, however its hydrolysis in grain systems is very limited. In this study, α-amylase assisted pullulanase was used to debranch rice flour (RF) in the first extrusion to produce amylose, and the effect of 2 %–8 % glyceryl monostearate (MG) on the structure, physicochemical and digestive properties of debranched RF was investigated in the second extrusion. The amylose content and chain length distribution results showed an increase in amylose content of 201.65 % compared to RF, as well as a shortening of chain length. The solubility and swelling power exhibited a decreasing trend followed by an increase with increasing MG content, reaching their lowest values at 6 %. The extruded rice flour-monoglyceride complexes (EERF-MG) exhibited V-shaped structures with a higher degree of integral intensity than RF. Thermal characterisation revealed that the thermal stability of all samples decreased following extrusion. The RS content of the EERF-MG increased significantly, with the addition of 6 % MG exhibiting the highest RS content of 60.22 %. Overall, extrusion conditioning using dual enzymes and co-processing with monoglyceride complexes significantly improved the anti-digestibility of RF, making it suitable for continuous industrial production.