Characterization of differently sized granule fractions of yellow pea, cowpea and chickpea starches after modification with acetic anhydride and vinyl acetate

The effect of reagent type on the properties of acetylated starches was studied for yellow pea, cowpea and chickpea starches after modification with acetic anhydride and vinyl acetate. Samples modified with vinyl acetate showed higher swelling volume and peak viscosity than those acetylated with acetic anhydride for the same starch. In addition, the reagents reacted differently towards granules having different sizes as present in un-fractionated starch. After sieving of the acetylated starches, the degree of substitution (DS) differed for the differently sized starch granules acetylated by the rapidly reacting acetic anhydride but not for the size fractions obtained from the starches acetylated by the slowly reacting vinyl acetate. Smaller size granule fractions exhibited larger swelling volume and higher peak viscosity as compared with the corresponding larger size fractions. The reagent type and granule size are important factors for pasting and swelling behaviours of acetylated granular starches.