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Structure and digestibility properties of resistant rice starch cross-linked with citric acid

ABSTRACT The objective of this present study was to determine the structural, physicochemical, and in-vitro digestibility properties of cross-linked rice starch with citric acid (CARS). Native rice starch (NRS) was cross-linked with different concentrations of citric acid (0, 1, 10, and 30%, w/w) of starch dry basis. The SEM results showed that cross-linking with citric acid induced changes in the morphology of starch granules. Compared with NRS, a new peak at 1734 cm−1 appeared in FT-IR spectra of CARS samples, except CARS1. In the X-ray diffraction patterns, crystalline peaks of all CARS samples became much smaller or even disappeared, as compared to that of NRS. 13C NMR spectra of CARS10 and CARS30 showed new peaks at about 45.55 ppm; in particular, an additional peak at 178.94 ppm occurred in the spectrum of CARS30. The swelling factor, light transmittance, thermal properties, and pasting properties of CARS were significantly lower than those of NRS. Furthermore, resistant starch contents of NRS were significantly increased, while the rapidly digestible starch and slowly digestible starch contents of NRS were significantly decreased after cross-linking with citric acid. Therefore, cross-linked rice starch with citric acid showed potential for application as a dietary fibre source in the food industry.