Effect of a dual modification by hydroxypropylation and acid hydrolysis on the structure and rheological properties of potato starch

Abstract

Potato starch modified with varying hydrolysis time and propylene oxide content was prepared to investigate the structure and rheological properties of acid-hydrolyzed-hydroxypropylated potato starch (AHP). The preceding acid hydrolysis, which altered the surface and interior properties of the starch granules, led to increased degree of hydroxypropylation. Pronounced differences in structural characteristics of starch were observed with changing hydrolysis time. Any increase in the hydrolysis time or propylene oxide content resulted in an increase in the flow behavior index and a decrease in consistency coefficient of the dual-modified starch. The gelling and gel properties appeared to be governed by the characteristics of starch molecules, i.e., samples with medium molecular weight and a relatively low degree of hydroxypropyl substitution were characterized by superior gelling ability and gel strength. The relationship between the properties of the sol-gel transition and the degree of the dual modification was further confirmed by examining the starch microstructure and changes in water distribution. The current study provides basic knowledge required for the use of AHP in such useful applications, as coating, encapsulation and hydrogel formation, in the food and pharmaceutical industries.