The effect of hydroxypropylation on the structure and physicochemical properties of native, defatted and heat-moisture treated potato starches

Abstract

Potato starch was physically modified by heat-moisture treatment [HMT] (100 °C, 16 h, 30% moisture) and defatting (75% n-propanol water, 7 h). Heatmoisture treatment decreased the X-ray diffraction intensities and altered the X-ray diffraction pattern from ‘B’ to ‘A + B’. The gelatinization enthalpy (ΔH), Brabender viscosity (at 95 °C), swelling factor (SF) and amylose leaching (AML) decreased on heat-moisture treatment. Whereas, gelatinization transition temperatures (GTT), and thermal stability increased on heat-moisture treatment. Defatting increased the X-ray diffraction intensities and altered the X-ray pattern from ‘B’ to ‘A + B’. GTT, ΔH and thermal stability increased on defatting, whereas, SF, AML and Brabender viscosity (at 95 °C) decreased on defatting. The reaction conditions used during hydroxypropylation disrupted double helices within the amorphous regions and altered crystallite orientation (native > defatted > heat-moisture treated). Hydroxypropylation with propylene oxide at various levels of molar substitution showed that the degree of accessibility of hydroxypropyl groups into the amorphous regions of the starch granule followed the order: heat-moisture treated > native > defatted. Hydroxypropylation decreased GTT, AML and ΔH, and increased the SF of native, defatted and heat-moisture treated starches.