Abstract
Oleyl potato starch (OA-PS) was prepared by lipase-catalyzed solid-phase synthesis. PS retaining AY-Amano 30G as a lipase (PS/Lip) was prepared by immersing in the lipase solution, and by dehydrating with ethanol before air-drying. PS/Lip and oleic acid (OA) were incubated in n-hexane or without a solvent, and then unreacted OA was thoroughly eliminated by washing with n-hexane before air-drying to respectively obtain OA-PS or OA-PS (solvent-free). The OA-PS samples respectively showed the structural compositions of PS (as glucose residue) of OA = 30:1 and 286:1 (molar ratio). Their crystallinity evaluated by polarizing microscopic observation and X-ray diffractometry and their digestibility with α- and β-amylase were similar to those of PS. The OA-PS samples acquired significantly higher thermal structural stability, as evaluated by DSC, than that of the PS and control samples, and exhibited improved pasting properties in terms of a markedly lower swelling index and peak viscosity by RVA, as well as easier vaporization of water from the gelatinized suspension and higher heat-resistance for maintaining the swollen starch granules at 110°C for 30 min than those of the PS and control starches. In particular, OA-PS was superior to OA-PS (solvent-free) in these structural and pasting characteristics. OA-PS also exhibited a decreased surface tension with increasing concentration. Oleylation with lipase should thus be valuable for improving the multiple functional properties of starch.
