Changes in Properties of Starches Heated in Monoglycerides

Abstract

Property changes in three varieties of starch (normal corn, waxy corn and wheat) heated in three varieties of monoglycerides (glycerin monostearate (MS), glycerin monooleate (MO) and glycerin monolinolate (ML)) were investigated. The starches were heated at 150°C for 1 h under open-air conditions. The heated starches were thoroughly washed with chloroform and dried. Little change in the shape of starch granules in all samples was observed on SEM images. Differential scanning calorimetry patterns were different among the starch and monoglyceride varieties with the decrease in enthalpy ratios compared to the control being 31% for normal corn starch in ML ; 20% for waxy corn starch in ML ; and 8% for wheat starch in ML. Rapid visco-analyzer patterns were different among the starch and monoglyceride varieties with the maximum viscosity peak ratio compared to the control being 2% for normal corn starch in ML ; 0% for waxy corn starch in ML ; and 8% for wheat starch in ML. The extent of amylose degradation was different among starch samples : 65% for normal corn starch in ML and 43% for wheat starch in ML. Gel permeation chromatography using a Toyopearl HW-65 column showed only one sharp peak in all the patterns of starch samples heated in ML, indicating amylopectin decomposition products with an average molecular weight of 1800. In contrast to the results of ML, changes in starch properties were small in the samples heated in MS. These results suggest that monoglycerides might easily penetrate into starch granules, forming radicals in an unsaturated fatty acid moiety with heating, and these starch components might be directly and/or indirectly attacked by these radicals and decompose to a dextrin-sized product.