Abstract
Starch isolated from rhizomes of edible canna (Japanese-green cultivar) was modified by acetylation in order to reduce retrogradation and increase gel stability. Acetylation was carried out by treating the starches with 5, 7 and 9 % (w/w) of acetic anhydride at 25 °C and pH between 8.0–8.5. The extent of acetylation increased proportionally with concentration of acetic anhydride used. The percentages of acetyl group determined by titration method were 1.53, 2.09 and 2.53. Examining under scanning electron microscope revealed that all of modified starches were still in intact granular form and there was no difference between native and modified starches. The viscoamylographs of 6% starch determined by Rapid Visco Analyzer at 160 rpm showed that acetylation decreased the pasting temperatures and slightly decreased the hot paste viscosity. The setback values of acetylated starches were approximately 35–43 % lower than those of native starches. This indicated that the retrogradation of canna starch was substantially reduced by acetylation. Pasting profiles of acetylated starches analyzed at agitation rates and pHs in ranges of 160–480 rpm and 2.6–6.8 were similar to those of native starch. The firmness (hardness) of canna starch gel was analyzed by texture analyzer using a 20 mm diameter-cylindrical plunger. With 6% starch solids in water at pH 6.8, all acetylated canna starches gave gels that were much less firm than that of native starch (197, 192, 205 and 2,392 g 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 canna starch could be reduced by acetylation.
Keywords
Edible canna starch; Starch modification; Acetylation; Viscosity; Gel
