Effect of hydroxypropylation and alkaline treatment in hydroxypropylation on some structural and physicochemical properties of heat-moisture treated wheat, potato and waxy maize starches

Hydroxypropylation was carried out on heat-moisture treated (HMT) wheat, potato and waxy maize starches. Hydroxypropylation increased swelling factor and amylose leaching of both native and HMT starches. Hydroxypropylation of HMT starches reduced enthalpies of gelatinization and amylopectin retrogradation more than for the corresponding non-HMT hydroxypropylated starches. This indicates that heat-moisture treatment increases the derivatization of amylopectin. Disruption and reorientation of amylopectin double helices during heat-moisture treatment could facilitate the access of reaction reagent to the highly ordered crystalline regions resulting in greater derivatization. Cold paste viscosity was greatly increased with high pasting stability when hydroxypropyl groups were introduced to HMT wheat and potato starches. Alkaline treatment increased gelatinization temperature of all the starches but enthalpy was unaffected. Amylose leaching and swelling factor greatly increased in wheat but decreased in potato and waxy maize starches with alkaline treatment. This increased amylose leaching and swelling factor along with greater reduction of amylose–lipid complex endotherm of wheat starch by alkaline treatment is consistent with the disruption of amylose–lipid complex. The amylose–lipid complex is susceptible to hydrolysis in alkaline conditions. Heat-moisture treatment had no influence on transition parameters of amylose–lipid complex.