Physicochemical Properties of Starches from Sri Lankan Rice Varieties

Abstract

Physico-chemical properties; amylose content, swelling power, pasting properties by Rapid Visco Analyzer (RVA), thermal properties by Differential Scanning Calorimeter (DSC), and enzymatic digestibility of starches isolated from 19 different Sri Lankan rice varieties were analyzed. Significant variation was shown in all the tested properties among tested varieties in which the amylose content varied from 16.0% to 34.7%. Amylose content appears to be the major factor controlling almost all physico-chemical properties of rice starch, as it showed significant correlations to all other properties tested. It correlated negatively to the peak and breakdown viscosities by RVA and enzyme digestibility but positively to all other tested properties. The peak and onset gelatinization temperatures and enzyme digestibility correlated to all properties except enthalpy for starch gelatinization. The peak and onset gelatinization temperatures, as well as the blue value, showed negative correlations to the peak and breakdown viscosities, indicating the importance of low amylose for easy starch pasting. According to our results, low amylose starches started to gelatinize at lower temperatures. During heating and cooling, such starch slurry showed higher peak and breakdown viscosities, but resulted in a softer gel. Low amylose starch was also easily digestible by enzymes. These properties are probably associated with the reduced compactness in the amorphous area of starch granules. Due to lower amylose in the amorphous area, loosely packed starch granules result in higher swelling power and disorganization with heating.