Functional, physicochemical and retrogradation properties of sword bean (Canavalia gladiata) acetylated and oxidized starches

The functional and physicochemical properties of native and chemically modified starches of Sword bean (Canavalia gladiata) were investigated. The starch yield was 31% (on whole seed basis). The chemical composition of the native starch is as follows: 0.17% crude protein, 0.08% crude fibre, 0.14% fat, 0.87% ash, carbohydrate determined by difference was 85.60%, while the energy value was 1437.64 KJ Kg−1. The native starch was chemically modified by oxidation (with sodium hypochlorite) and acetylation (with acetic anhydride). The scanning electron micrograph SEM of the starches shows a smooth ellipsoids with slight indentation in the center of the granules, however, oxidation and acetylation causes rupture (<10%) of the granules. The water binding capacity of the modified starch increased after chemical modification in the following order: Acetylated starch > Oxidized starch > Native starch The solubility of all the starches increased as the temperature was increased with the Oxidized starch having the highest value. Swelling power measured from 50 to 90°C at 10°C intervals, also increased as the temperature increased among the starches. The order is similar to that recorded for the water binding capacity. The oil and water absorption capacity ranges from 2.9–3.6 g/g and 2.2–2.7 g/g, respectively, for all the starches. The pasting properties show the starches to be a Type C starch with restricted swelling which is typical of legume starches. Viscosity of the starch was increased by acetylation while oxidation reduces it. The gelatinization temperature (onset, peak and conclusion) was higher in the native starch than the chemically modified starches, while its enthalpy was lower.