Efficiency, functionality, and multi-scale structure of citric acid esterified glutinous rice starch synthesized via infrared radiation

To simplify the process, decrease output cost, and limit the amount of wastewater and gas generated in the production of esterified starch, highly citrate-substituted glutinous rice starch was prepared using infrared radiation (IR) technology. Physicochemical properties and multi-scale structure of different starch were characterized to assess effectiveness of IR in starch esterification. Absorption at 1749 cm-1 in the Fourier-transform infrared spectrum was determined in either IR-citric acid modification (ICM) or dry heat-citric acid modification (DCM), confirming occurrence of esterification. The use of IR shortened synthesis time (7 min) for ICM compared with DCM (5 h) to an equivalent degree of substitution of 0.154. Furthermore, while functional properties of ICM and DCM were not significantly different (p > 0.05), they featured better thermal stability, anti-retrogradation, and digestion resistance compared with native glutinous rice starch. IR and esterification treatment destroyed crystalline regions in glutinous rice starch and decreased the order of molecular chains. The loss of the crystalline region was consistent with the absence of endothermic peaks in IRM, ICM, and DCM as indicated by differential scanning calorimetry. The results suggest that the use of IR technology for citric acid esterification of glutinous rice starch is an effective alternative method for preparing high contents of thermally stable resistant starch, and provide insights regarding the potential industrial application of IR technology for diversifying starch modification methods.