Effect of cross-linking with epichlorohydrin on the properties of cassava (Manihot esculenta Crantz) starch

Cassava starch was cross-linked with epichlorohydrin (EPI) at 45 degrees C for 2 h in three different media which include water, water in the presence of a phase transfer catalyst (PTC) and N,N-dimethylformamide (DMF). The products were characterized by determining their physicochemical, thermal and retrogradation properties. In aqueous medium, the use of a PTC, tetrabutylammonium bromide (TBAB) produced derivatives with higher degree of cross-linking than those prepared without the use of the catalyst. The degree of cross-linking was found to be higher using the same concentration of EPI when the reaction was carried out in DMF At low levels of cross-linking, the peak viscosity of the cross-linked starches increased in comparison to that of the native starch. With increasing degree of cross-linking, the peak viscosity showed a significant reduction. The swelling volume, solubility and light transmittance of the starch pastes were lower for the modified starches. The cross-linked starches showed slightly reduced values for the gelatinization temperatures, T-onset, T-peak and T-end. The enthalpy of gelatinization of the modified starches increased with increase in the degree of cross-linking. The modified starches exhibited higher water-binding capacities (WBC) than the native starch; but with increase in the degree of cross-linking, there was a gradual decrease in WBC. The in vitro alpha amylase digestibility of the modified starches decreased gradually with increase in the level of cross-linking.