Edible Canna (Canna edulis) Starch Modified by Acetylation

Abstract

Starch isolated from rhizomes of edible canna (Japanese-green cultivar) was modified byacetylation in order to reduce retrogradation and increase gel stability. Acetylation was carried out bytreating the starches with 5, 7 and 9 % (w/w) of acetic anhydride at 25 ÌC and pH between 8.0 - 8.5.The extent of acetylation increased proportionally with concentration of acetic anhydride used. Thepercentages of acetyl group determined by titration method were 1.53, 2.09 and 2.53. Examiningunder scanning electron microscope revealed that all of modified starches were still in intact granularform and there was no difference between native and modified starches. The viscoamylographs of6% starch determined by Rapid Visco Analyzer at 160 rpm showed that acetylation decreased thepasting temperatures and slightly decreased the hot paste viscosity. The setback values of acetylatedstarches were approximately 35-43 % lower than those of native starches. This indicated that theretrogradation of canna starch was substantially reduced by acetylation. Pasting profiles of acetylatedstarches analyzed at agitation rates and pHs in ranges of 160-480 rpm and 2.6-6.8 were similar tothose of native starch. The firmness (hardness) of canna starch gel was analyzed by texture analyzerusing a 20 mm diameter-cylindrical plunger. With 6% starch solids in water at pH 6.8, all acetylatedcanna starches gave gels that were much less firm than that of native starch (197, 192, 205 and 2,392g for 1.53, 2.09, 2.53% acetyl groups and native Japanese-green starches, respectively). The result of%syneresis values obtained from freeze-thaw stability confirmed that the retrogradation of cannastarch could be reduced by acetylation.

Keywords : Edible Canna Starch / Starch Modification / Acetylation / Viscosity / Gel