Effect of pullulanase debranching and storage temperatures on structural characteristics and digestibility of sweet potato starch

The effect of autoclaving (120 °C/30 min), debranching (2% pullulanase/1 h) and storage at 4 °C (DS4) or 32 °C (DS32) or 60 °C (DS60) for 24 h on starch fractions, functional, pasting, thermal and structural properties of sweet potato starch was investigated. Results showed that DS4 sample displayed the lower functional properties than other modified starches. Debranching showed a significant increase in the apparent amylose content of native starch from 18.56% to 25%. A higher yield of RS (28.76%) was observed in debranched starch stored at 4 °C (DS4) due to the higher degree of retrogradation. All debranched starches showed a substantial decrease in pasting profile and higher gelatinization temperatures than in native starch. B + V X-ray diffraction pattern was observed in debranched starches with increased crystallinity value. The scanning electron micrographs of debranched starches showed rough plate-like surfaces with irregularly shaped structures were observed due to debranching and retrogradation during storage. The study concludes that a combination of autoclaving, debranching and subsequent storage at 4 °C is best technique to produce a higher amount of resistant starch in the sweet potato starch.