Esterified unpopped foxnut (Euryale ferox) starch: molecular and rheological characterization

BACKGROUND Acetylated‐based starches are broadly used in the food industry as emulsifiers, and as thickening and film‐forming agents. Better understanding of the structural and rheological parameters would facilitate the selection of optimal acetylated starches for particular applications. Nuclear magnetic resonance (1H‐NMR), Fourier‐transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) patterns, and rheological properties, including elasticity (G'), loss (G") moduli, complex viscosity (η*) and study shear stress (δ), were determined for acetylated fox nut starch (FNS) samples. RESULTS The degree of substitution (DS) varied significantly with increasing acetyl concentration from 2–6%. Nuclear magnetic resonance analysis of acetylated FNS showed an additional chemical shift at 2.08 ppm in comparison with native FNS, confirming the linking of the H or the –OCH3 group. The acetylated FNS starches showed better short‐range ordering of molecules, as confirmed by FTIR. A significant increase in the functional and gelatinization properties with increasing acetyl concentration was observed. The power law parameters (n, K) and dynamic moduli (G' and G") increased with increasing acetyl concentration and presented shear thinning behavior. The gelatinization peak temperature and enthalpy decreased with increasing acetyl concentration. CONCLUSION The observed DS below 2.5 would mean safe food consumption and the significant alteration of functional and structural properties with varying acetyl content will extend the use of FNS in food and allied industries. © 2023 Society of Chemical Industry.