Solvent-free synthesis of starch citrate via dry heat reaction: An in-depth analysis on structural and physicochemical properties

The main objective of this study was to determine the feasibility and validity of the solvent-free dry heat reaction by investigating the structural and physicochemical properties of the starch citrates. Initially, a solid blend of native corn starch (NCS) and citric acid (CA) was heated in a preheated oven followed by further heating under continuous stirring to facilitate the reaction. The presence of ester bonds in the starch citrates was confirmed using Fourier Transform Infrared Spectroscopy (FTIR), which revealed a new absorption peak at 1738 cm −1 . The starch citrates (SC) showed an increased thermally stable resistant starch (RS) content, with a thermally stable RS content of 74.37% and enhanced solubility. The solid-phase prepared starch citrates demonstrated reduced relative crystallinity, decreased swelling power, and lower pasting viscosities than native corn starch. Overall, these findings suggest that the solvent-free method of dry heat reaction between corn starch and citric acid is a viable technique for green preparing starch citrates. • Stirring and heating techniques increase the resistant starch content in starch citrate. • Suitable stirring and heating proved to be the effective method for rapid preparation. • The content of thermally stable resistant starch in starch citrate is increased. • This developed dry heat method can be used in large-scale preparation of starch citrate.