Comparison of the structure and properties of hydroxypropylated acid-hydrolysed maize starches with different amylose/amylopectin contents

Abstract

Dually modified regular maize starch (RMS) and high-amylose maize starch (HAMS) were successfully prepared by first acid hydrolysis and subsequently hydroxypropylation. The effects of hydrolysis time (0–24 h) and propylene oxide (PO) content (10–30%) on the structure and physicochemical properties were investigated. The molar substitution (MS) of HAMS samples (up to 0.163) was generally higher than that of RMS samples (up to 0.149), suggesting the higher reactivity of amylose for hydroxypropylation. Besides, PO content had a greater influence on MS whereas the effect of acid hydrolysis time was minor. For both starches, the dual modifications did not cause apparent changes to the granule morphology but reduced gelatinisation temperatures and enthalpy; and a higher PO content led to higher relative crystallinity. These results suggest that hydroxypropylation occurred mainly on the surface of HAMS granules and had little influence on the compact granular structure, whereas this reaction impacted the internal structure of RMS much more. The rheological study shows the introduced hydroxypropyl bulky groups weakened the entanglements between amylose chains or amylopectin chains with long branches. Thus, this work provides insights into the rational design of modified starch products containing different amylose/amylopectin contents with tailored properties.