Effects of annealing time on structure and properties of sweet potato starch

Background and objectives Sweet potato starch is an important industrial raw material, but it is not applied widely because of its disadvantages including high regeneration rate and poor paste stability. In this study, the starches were incubated at 50 degrees C for 1, 3 and 5 days, their structure and properties were determined, and annealing (ANN) time effects on sweet potato starch were investigated. Findings X-ray diffraction revealed that both native and annealed sweet potato starches had the A-type crystalline pattern. After ANN for 3 days or less, the relative crystallinity, short-range order and enthalpy of starch decreased slightly due to partial gelatinization, however long ANN for 5 days resulted in their increase. ANN increased the pasting temperature (To, Tp, Tc), narrowed the gelatinization temperature range (Tc-To), and promoted an increasingly significant reduction in peak viscosity, breakdown, and setback with the increase in ANN time. Also, ANN increased the cumulative particle size of sweet potato starch granule. Conclusion 5 days' ANN treatment had the greatest effect on the starch, while short-time ANN for 1 day and 3 days had only the little effect. Right ANN time could obviously improve the starch structure and properties, like good thermal stability and weak retrogradation. Significance and novelty This study provides valuable conclusions from the ANN time level, confirms that long-time ANN is very necessary, and creatively proved by the short-range order and cumulative particle size.