Starch Citrate Synthesis from Diverse Thai Rice Cultivars: A Study on Resistant Starch Enhancement and Physicochemical Changes

This study investigates the synthesis and characterization of starch citrate derived from five Thai rice cultivars: Rice, Riceberry, Homnil, Red Jasmine, and Thubtim Chumphae using citric acid esterification. The objective was to enhance resistant starch (RS) content and assess changes in structural and functional properties. Native rice starches were chemically modified and evaluated through resistant starch assays, Fourier-transform infrared spectroscopy (FTIR), Rapid Visco Analyzer (RVA), scanning electron microscopy (SEM) and water absorption index. Results showed a significant increase in RS content in citrate-modified flours, with white rice exhibiting the highest RS value (55.04%). FTIR confirmed ester bond formation through the appearance of C=O stretching bands at 1734–1740 cm–1, SEM images revealed pronounced granule surface disruption post-modification. The physicochemical changes confirm successful citric acid crosslinking, which improves starch resistance to enzymatic digestion. These findings highlight the potential of citric acid esterification in developing functional starches with health-promoting properties and enhanced thermal and morphological characteristics.