Synthesis of hydroxypropylated debranched pea starch with high substitution degree in an ionic liquid, and its characterization and properties

Abstract

Hydroxypropylation of debranched pea starch (DPS) has been carried out effectively in an ionic liquid, 1-butyl-3- methylimidazolium chloride, in order to shorten the long time required by starch being normally hydroxypropylated and improve the characteristics of pea starch (PS). As a result, hydroxypropylated debranched pea starch (HDPS) with molar substitution up to 1.34 has been obtained in homogeneous system within 3 h, which was much less than time (18 h) required by normal hydroxypropylation of starch. Based on the synthesis, HDPS was further characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy and transflective polarizing microscope, respectively, and some of its properties were also compared with those of PS, DPS and hydroxypropylated pea starch (HPS). The experimental results indicated that the crystalline structure of PS belonged to a C-type; and one of DPS was between B-type and C-type, whereas HDPS structure was almost completely amorphous. The debranching and hydroxypropylation evidently influenced the pasting behavior and thermal properties of PS. The morphology and size of DPS and HDPS particles were remarkably different from those of PS owing to hydroxypropylation and debranching. The peak intensity of –OH groups in DPS and HDPS was evidently weakened by debranching compared with FTIR spectra of PS. The debranching resulted in the reduction in swelling power of DPS, but the hydroxypropylation led to the increase in the swelling power of DPS and HDPS.