The effect of heat moisture treatment on crystallinity and physicochemical-digestibility properties of purple yam flour

Abstract Purple yam flour was successfully modified by heat moisture treatment (HMT) in three cycles using an oven (OHMT) and autoclave (AHMT) (100°C and 120°C; moisture level: 15%, 22%, and 30%). X-ray diffraction (XRD) and FTIR were used to characterize the molecular structural change due to thermal treatment. The native and modified purple yam flours’ swelling capacity, solubility, and digestibility (RDS, SDS, and RS) parameters were studied. The OHMT and AHMT treatments decreased swelling capacity, solubility, and RDS, while RS and SDS increased compared to native. FT-IR analysis showed an absorption band decrease at 930, 1022, 1080, 1155-1150, 1641, 2930, and 3400 cm-1 for the modified flours. After HMT, the Diffractogram pattern showed starch type change from B to A with four core peaks at 2θ: 15˚; 17˚; 18˚ and 23˚. OHMT and AHMT increased the relative crystallinity of all samples except OHMT215 (oven temperature: 120˚C and moisture level: 15%) to 30.80%. This study indicated that the two treatments improved purple yam’s functional properties, therefore it is potentially applied in many food industries.