Hydrothermal treatment of water yam starch in a non-granular state: slowly digestible starch content and structural characteristics.

UNLABELLED: Gelatinized water yam starch was subjected to hydrothermal treatment (25, 30, and 35% moisture content for 1, 8, 16, and 24 h at 100 °C) and characterized by X-ray diffractometry, solid-state ¹³C cross-polarization and magic-angle spinning nuclear magnetic resonance, differential scanning calorimetry, and digestibility analysis. The slowly digestible starch (SDS) content of the starch treated at 30% moisture content for 24 h reached 49.1%, 31.9% higher than that of the control starch. The B-type pattern of native starch was re-crystallized to the A-type by hydrothermal treatment. The SDS content showed negative correlations with T(o), T(p), T(c), and T(r), but showed a positive correlation with melting enthalpy. Furthermore, SDS was positively correlated with hydrothermal reaction time, moisture content, relative crystallinity, and the double-helix proportion. The structural changes in hydrothermally treated water yam starches resulted in the enhancement of SDS. PRACTICAL APPLICATION: The hydrothermally treated water yam starch could be used as a food ingredient for slow-energy supply or dietary fiber.