Study on compatible characteristics of wheat and purple sweet potato starches

Abstract

In this study, the compatibility of purple sweet potato (C-type) and wheat starches (A-type) was characterised by measuring glass transition temperature, equilibrium melting temperature and interaction parameter. The glass transition temperature of mixed starch containing 40% and 60% moisture drifted toward the high temperature with the increase in purple sweet potato starch content. The glass transition temperature of all mixed starches has a single peak between wheat and purple sweet potato starches. The equilibrium melting point temperature of all samples containing 60% moisture was lower than those containing 40% moisture. Under the same water content, the equilibrium melting point temperature of mixed starch decreased slightly as compared with that of wheat starch and no significant difference was observed among the mixed starches. The interaction parameters of wheat and purple sweet potato starches remained negative. The result indicated that wheat starch was compatible with purple sweet potato starch. The addition of 1%–15% purple sweet potato starch increased trough viscosity, breakdown, final viscosity, storage modulus (G’) and loss modulus (G”), decreased loss tangent (tan δ) and effectively improved the freeze-thaw stability of wheat starch gel. The honeycombed structure of wheat starch gel after lyophilisation became small and uniform with the increase in purple sweet potato starch content. Hence, wheat starch has good compatibility with purple sweet potato starch.