Effect of citric acid esterification on the structure and physicochemical properties of tigernut starch

In this work, esterified tigernut starch with citric acid (ETSC) was prepared for the first time, and its structure, in vitro digestibility, and Pickering emulsifying capacity were investigated. The formation of ETSC was confirmed by SEM (Scanning electron microscopy), XRD (X-ray diffraction), FTIR (Fourier-transform infrared spectroscopy), and solid-state 13C NMR (Nuclear magnetic resonance), and the citric acid dosage in the preparation process was positively correlated with the degree of substitution (DS) of ETSC. With an increase in DS, the solubility and swelling power of ETSC decreased, the crystallinity degree declined, and the proportion of resistant starch (RS) increased rapidly. The increase in DS could also enhance the wettability of ETSC, thus improving the Pickering emulsifying ability of ETSC. The high ETSC concentration (c) and suitable oil phase volume ratio (φ) of the Pickering emulsion were beneficial to its formation and stability. Moreover, the macroscopic viscosity index (MVI) and elastic index (EI) of the emulsion were also positively related to the DS of ETSC.