Ordered structure of preformed V-amylose inclusion complex with 5-heptadecylresorcinol

Abstract

5-Heptadecylresorcinol (ARs-17) is an amphiphilic phenolic lipid in grain bran with multiple bioactivities. In this study, the relationship between the crystalline structure, thermostability, morphological properties and in vitro digestibility of high amylose maize starch (HAMS) and preformed V-amylose (V6a, V6h, V7a, V7h, V8a, V8h) inclusion complexes with ARs-17 were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscope (SEM). XRD and FTIR results revealed that both HAMS and V-amylose could form V6-type crystalline inclusion complexes with ARs-17, and the hydrophobic alkyl chain of ARs-17 located in the amylose helix cavity, while the hydrophilic phenolic hydroxyl group of ARs-17 located outside the helix. DSC analysis demonstrated that the complexation of V-amylose and ARs-17 was beneficial to the formation of stable type VIIb complexes with higher peak temperature over 140 °C, while the endothermal peak of HAMS-ARs-17 inclusion complex was only around 115 °C. SEM images detected that V-amylose and their complexes were spherical shape with the close-packed structure and aggregated together. By parameterizing digestion kinetics through logarithm-of-slope analysis (LOS) plot fitting, V6a-ARs-17 and V6h-ARs-17 inclusion complexes exhibited the lowest digestibility. This study suggests the great potential to apply V-amylose as functional ingredient for improving both processing and digestion stability of alkylresorcinols and thereby enhancing its bioaccessibility.