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Abstract Citric acid-esterified rice starch was synthesized using a one-step reactive extrusion method. The structure, physicochemical properties, and digestibility of the esterified starch were then measured. An in vitro digestion study indicated that esterification significantly increased the level of resistant starch (RS) in the samples. Fourier transform infrared spectroscopy (FT-IR) confirmed esterification had occurred between the citric acid and starch, with a new peak appearing at around 1730 cm−1. X-ray diffraction indicated that esterification caused a decrease in the degree of crystallinity in the starch. The swelling power and solubility of starch citrate were both lower than unmodified starch. Turbidity measurements suggested there was a slower rate of reassociation in starch citrates during storage. These results suggest that citric acid esterification promoted cross-linking within the starch that significantly reduced its digestibility. This simple method may be useful for the creation of healthier starchy foods. Graphical abstract Image 1 Highlights • One-step extrusion was developed as a means to produce starch citrate. • Citric acid esterification increased the resistant starch content of rice starch. • Physiochemical and structural analysis indicated the formation of a cross-linked structure in starch citrate. • This method may be suitable for commercial production of healthier starchy foods. [ABSTRACT FROM AUTHOR]

In this study, starch citrates were synthesized by superheated steam (SS) treatment without changing the granule structure of starch. The degree of substitution (DS) of starch citrates prepared in present study was ranged from 0.015 to 0.064. Fourier transform infrared spectroscopy confirmed that citric acid (CA) and starch were successfully esterified with an absorption peak appeared at 1735 cm−1. In vitro digestion results revealed that the content of resistant starch (RS) was significantly increased by citric acid esterification, which was attributed to the cross-linked structure of starch and the inhibition of gelatinization and swelling. According to the physicochemical properties analysis, the pasting temperature of rice starch citrates were significantly increased by citric acid treatment, while the swelling power and gelatinization enthalpy were significantly decreased and the short- and long-range molecular order of the starch was disrupted after the esterification reaction. These results indicated that it is a feasible method to synthesize starch citrate by superheated steam to increase resistant starch, and it could be used as an alternative approach for preparing starch citrate to conventional hot air treatment. • A superheated steam technology was adopted to synthesize starch citrates. • The starch citrates were maintaining the granule structure of starch. • The resistant starch content was increased by the formation of starch citrates. • The esterified and cross-linked structure was formed in starch citrates. • The inhibition of gelatinization and swelling was found in starch citrates. [ABSTRACT FROM AUTHOR]