Physicochemical, rheological and structural characterization of acetylated oat starches

Starches isolated from three different varieties of oat were modified with acetic anhydride to make starches with high contents of type 4 resistant starch (RS4). The acetyl group percentage (Ac) and degree of substitution values (DS) of oat starches ranged from 0.64 to 1.50 and 0.02–0.05, respectively. The absorption peaks at 1737 cm−1, 1337 cm−1 and 1243 cm−1in the FTIR spectrum confirms the presence of acetyl groups in the starch molecule. SEM micrographs revealed significant changes in external morphology of acetylated starches due to the formation of small pores. XRD analysis reflects the formation of amylose–lipid complex with decreased crystallinity in acetylated starches. The viscosity of starches decreased on acetylation, exhibited shear-thinning behavior as reflected from the convex shaped graph with viscosities of acetylated starches following the order; SKO90 > SKO20 > Sabzaar.