Effects Of Cross-Linking And Acetylation On Some Physicochemical Properties Of Cowpea (Vigna Unguiculata) Starch

Author(s): Mwanjala Alfred Mwasaru, Ken-Ichi Ishibashi

The effects of cross-linking with POCl3 and acetylation, singly and in combination on the physicochemical properties of cowpea starch were investigated. Cross-linking enhanced the solubility and swelling power but generally decreased paste clarity of cowpea starch whereas acetylation improved the paste clarity. Both acetylation and cross-linking caused a decrease in the initial pasting temperature. The paste consistency at 95°C was significantly increased by cross-linking but was decreased upon acetylation and double modification. Acetylation improved the freeze-thaw stability of cowpea starch gels but the improvement upon cross-linking appeared to depend on the degree of substitution and the number of freezethaw cycles. Cross-linking and acetylation resulted in significant reductions in the onset (To) and completion (Tc) temperatures, and gelatinization enthalpy (ΔH) of the starch. Acetylation resulted in significant reductions in maximum storage modulus (Gmax’) and loss modulus (Gmax”) whereas crosslinking resulted in significant reductions in Gmax”. Overall, acetylation was more effective than cross-linking in modifying the pasting, freeze-thaw stability, and dynamic mechanical properties of cowpea starch.

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