Influence of amylosucrase-treatment on the retrogradation of waxy corn starch

Abstract

Waxy corn starch was modified by using amylosucrase (AS) from Neisseria polysaccharea for 1, 3, and 6 hr and retrograded at 4°C and 30°C for 1, 2, and 3 weeks. Branch-chain length distribution, thermal properties, crystallinity, and digestibility were changed by the AS-treatment. A chains (DP ≤ 12) decreased, while both B2 chains (DP 25-36) and B3 chains (DP 25-36) increased with increasing reaction time. Thermal properties of AS-treated starch such as the onset temperature, peak temperature, conclusion temperature, and melting enthalpy increased with enzyme reaction time. The X-ray pattern of AS-treated waxy corn starch changed from A- type to B- type, and peak intensity increased as the AS-treatment time increased. Slowly digestible starch (SDS) and resistant starch (RS) increased, while rapidly digestible starch (RDS) decreased. After the retrogradation at 4°C, the melting enthalpy of retrograded AS control and 1 hr samples was changed. In the case of the retrogradation at 30°C, only 1 hr samples showed differences in enthalpy. All retrograded AS-treated starches displayed nonsignificant difference in X-ray diffraction pattern. Only relative crystallinity of the retrograded 1 hr sample at 30°C increased from 17.1% to 17.8%. The contents of SDS and RS showed nonsignificant differences, but the RDS of retrograded AS control at 4°C decreased from 84.8% to 79.7%. In addition, the SDS of retrograded 1 hr sample at 30°C increased from 13.5% to 20.8%. In this study, the AS-treatment elongated branch-chain length, and influenced retrogradation of waxy corn starch. Thus, the retrogradation of AS-treated waxy corn starch was affected by branch-chain length and dimension of chains.