Effect of repeated heat-moisture treatments on digestibility, physicochemical and structural properties of sweet potato starch

• Sweet potato starch was modified by repeated heat-moisture treatments (RHMT).
• The RHMT-3 starch samples had the maximum SDS content of 19.61%.
• Thermo-stable SDS content reached the maximum (14.46%) by RHMT-3.
• Thermal and pasting properties were significantly changed by RHMT.
• RHMT changed the crystalline pattern from Ca to A type.

In the present study, the effects of repeated heat-moisture treatments (RHMT) on the in vitro digestibility, physicochemical and structural properties of sweet potato starch were investigated. The cycling times of RHMT ranging from 1 to 5 and heat-moisture treatment for 6 h were designated as RHMT-1, RHMT-2, RHMT-3, RHMT-4, RHMT-5 and HMT-6h, respectively. The results showed that as the cycling times of RHMT increased, the SDS content of starch samples increased gradually and reached the maximum (19.61%) by RHMT for 3 times, and the thermo-stable SDS content also increased and reached the maximum (14.46%) by RHMT-3, while the swelling power and solubility decreased gradually. Compared with the native starch, the gelatinization transition temperatures of modified starch samples were significantly increased, gelatinization enthalpy and gelatinization temperature range decreased markedly. The values of degree of gelatinization (DG) showed that RHMT caused some gelatinization of the starch granules. Moreover, the RHMT starch samples exhibited significantly increased pasting temperatures, reduced viscosities, and no longer exhibited traditional pasting profiles for the lack of a true peak viscosity and no breakdown, and the agglomerations of granules were found in them. The variation in infrared absorbance ratio of 1047 cm−1 and 1022 cm−1 of RHMT starch samples were consistent with that in relative crystallinity, and RHMT starch samples exhibited A type crystalline pattern. These results suggested that structural changes of sweet potato starch by RHMT significantly affected the digestibility and physicochemical properties.

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