Simultaneous determination of amylose content & unit chain distribution of amylopectins of cassava starches by fluorescent labeling/HPSEC

The fluorescent labeling of debranched starch/high-performance size-exclusion chromatography equipped with one column of Shodex OHpak SB-803HQ and two columns of SB-802.5HQ was proposed for simultaneous determination of amylose content and unit chain distribution of amylopectin of starch samples from four cassava varieties. Chromatograms obtained by refractive index (RI) response detection revealed that peaks of amylose and amylopectin fractions were completely separated, whereas only a peak of amylopectin was observed by fluorescent response detection. The amylose contents of cassava starch samples calculated from the RI response chromatograms were comparable to those determined by amperometric titration method and by overlaying the amylopectin profile on the profile of the starch isoamylolyzate. The values obtained for each starch sample were highly reproducible for duplicate analyses with standard deviations less than 0.6%. Distribution profiles of amylopectins from the starch isoamylolyzate were very similar to those obtained from fractionated amylopectins. Molar- and weight-based unit-chain fraction and ratio of A+B1/B2+B3 were close to those derived from profiles of fractionated amylopectins. Differences of mole fraction of A, B1 and B2+B3 chains and ratio of A+B1/B2+B3 determined from starch and fractionated amylopectin chromatograms of all four cassava starches were less than 2.7, 2.7, 0.15 and 0.12%, respectively.