Effect of Dual Modification on the Properties of Native Pearl Millet Starch

Background: A combination of heat-moisture treatment and citric acid was used to modify pearl millet starch in this study. Changes in structural, thermal and in vitro digestibility of the treated starches were investigated. Methods: Native starch was isolated using alkaline steeping method. Native starch was dual modified (Heat moisture treatment and citric acid) used for further analysis. To examine the granular morphology of dual modified starch using SEM, DSC, RC and in vitro starch digestibility assay was assessed to quantify the proportion of digestive starch fractions, including rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS). Result: Granules of the native starches of pearl millet varied from polygonal to circular or oval in shape. Indentations were observed on the surfaces of dual modified starch. Relative crystallinity was less than native starch. Profound increased gelatinization temperature was witnessed, meanwhile enthalpy of gelatinization was decreased. In the dual modified pearl millet starches, the percentage of RDS contents was significantly decreased. The resistant starch (RS) content of the treated starches, however, significantly increased from 11.48% in native starches to 19.40% in HMT starches and 28.3% in dual modified starches.