Blends of native and amylosucrase treated waxy starches complexed with fatty acid: digestibility and physicochemical properties

Abstract

Preparation of waxy starch-lipid complex is hampered by steric hindrance and short branch chains of amylopectin (AP). In the current study, starch-lipid complexes were prepared by using the blends of native and amylosucrase (AS) treated waxy corn starches and fatty acid (0.5 mM/g-starch) i.e. lauric acid (LA, C12:0) and palmitic acid (PA, C16:0). This study aimed to investigate the effects of branch chain length of starch and kinds of fatty acid on the complex content, X-ray diffraction pattern, thermal properties, digestibility, and rheological properties of the products. With increasing proportion of the AS-treated starch, branch chain length increased which led to an increase of apparent amylose content. The ability of starch to complex with fatty acids increased with branch chain length of AP and lipid chain length. The X-ray diffraction patterns of starch blends and starch-LA complexes showed a B-type polymorph, while that of starch-PA complexes revealed a B+V-type. The relative crystallinity, melting enthalpy, and viscoelasticity were increased and the digestibility was decreased owing to double helical structure formed by elongated branch chains. However, because the complexed fatty acid disrupted the double helical structure, relative crystallinity, melting enthalpy, and viscoelasticity were decreased and digestibility was increased with an increase in complex content. Meanwhile, though melting temperature of starch blends was decreased with increasing amount of AS-treated starch because of disordered arrangement of elongated branch chains, melting temperature of AS-treated starch increased after complexation with fatty acid due to ordered crystallinity of starch-lipid complex. In conclusion, this study demonstrated that the complexed fatty acid impairs the formation of double helical structure of elongated branch chains by AS treatment, which induces the changes in functional properties of waxy starch-lipid complexes.