Purpose: To analyze the physicochemical properties and in vitro digestibility of sweet potato starch phosphodiester prepared using sodium trimetaphosphate.

Methods: The physicochemical properties of sweet potato starch phosphodiester were analyzed by using infrared spectrometry (IR), differential scanning calorimetry (DSC) and rapid visco-analyser (RVA). In addition, an in vitro digestibility method was applied to investigate starch digestion performances.

Results: FTIR spectrum showed new absorption peaks at 1033 cm^-1 indicating that an esterification cross-linking reaction was found between sweet potato starch and sodium trimetaphosphate. Similar gelatinization temperature (70 ^oC), enthalpy change (10 J/g), and peak viscosity (600 cp) were obtained for sweet potato starch phosphodiester and the raw starch indicating that their gelatinization properties were identical. Compared with sweet potato starch, digestible starch content of sweet potato starch phosphodiester decreased sharply (from 63.4 to 15.8 %), while digestion resistance starch content increased significantly (from 14.5 to 58.7 %). Based on completion of starch hydrolysis, the glycaemic index (GI) of sweet potato starch phosphodiester was predicted to be 66.31.

Conclusion: Derived sweet potato starch phosphodiester presents higher digestibility and may be useful as a medium glycemic index (GI) food for diabetic patients.