THE EFFECT OF HYDROXYPROPYLATION ON THE STRUCTURE AND PHYSICOCHEMICALPROPERTIES OF NATIVE, DEFATTED AND HEAT-MOISTURE TREATED POTATO STARCHES

Potato starch was physically modified by heat-moisture treatment [HMT] (100 degrees C, 16 h, 30% moisture) and defatting (75% n-propanol wat er, 7 h). Heat-moisture treatment decreased the X-ray diffraction inte nsities and altered the Xray diffraction pattern from 'B' to 'A + B'. The gelatinization enthalpy (Delta H), Brabender viscosity (at 95 degr ees C), swelling factor (SF) and amylose leaching (AML) decreased on h eat-moisture treatment. Whereas, gelatinization transition temperature s (GTT), and thermal stability increased on heat-moisture treatment. D efatting increased the X-ray diffraction intensities and altered the X -ray pattern from 'B' to 'A+B'. GTT, Delta H and thermal stability inc reased on defatting, whereas, SF, AML and Brabender viscosity (at 95 d egrees C) decreased on defatting. The reaction conditions used during hydroxypropylation disrupted double helices within the amorphous regio ns and altered crystallite orientation (native,defatted > heat-moistur e treated). Hydroxypropylation with propylene oxide at various levels of molar substitution showed that the degree of accessibility of hydro xypropyl groups into the amorphous regions of the starch granule follo wed the order: heat-moisture treated > native > defatted. Hydroxypropy lation decreased GTT, AML and Delta H, and increased the SF of native, defatted and heat-moisture treated starches. (C) 1997 Canadian Instit ute of Food Science and Technology. Published by Elsevier Science Ltd.