Objective Effects of retrogradation time on the physicochemical properties and microstructure of Chinese chestnut starch were investigated, aiming to provide reference data for its processing and to further explore the retrogradation mechanism.

Method Starch of Castanea mollissima Blume was gelatinized, refrigerated at 3 ℃ for 1, 3, 7, and 14 d, and dried in a vacuum freeze dryer. Contents of total starch, amylose, and amylopectin as well as iodine blue value and retrogradation degree of the samples were determined. Microstructural changes of the starch as affected by the varied lengths of retrogradation time were observed under a scanning electron microscope. Pearson-coefficients of correlation between the starch physicochemical indexes and retrogradation duration were obtained.

Result The total starch content in the chestnut starch increased with increasing time of retrogradation and peaked on the 14 d at 73.02%. The content of amylose was also on an increasing trend that reached the highest at 36.14% on the last day of treatment as well. Meanwhile, the iodine blue value and retrogradation degree rose gradually and the water solubility index and swelling force of the treated starches became significantly lower than those of control with the changes shaped like the letter N. The time of in vitro digestion of the starch increased gradually with the retrogradation duration. The starting temperature (T_o), peak temperature (T_p), termination temperature (T_c), and crystal melting thermal enthalpy (ΔH) of the treatment starches were significantly lower than those of control. But there were no significant differences in the thermal properties between the treatment groups. Significant positive correlations were observed between the retrogradation degree and treatment time (P＜0.05,r=0.96) as well as between the iodine blue value and amylose content (P＜0.05,r=0.97). The 3D structure of the starch could be gradually restored in 1–7 d retrogradation but deteriorated at 14 d showing a rough surface on the gel.

Conclusion  Compared with native starch (0 d), the gelatinized and retrograded Chinese chestnut starch exhibited significantly decreased physicochemical properties. Additionally, retrogradation time had a notable impact on the starch's microstructure.