EXAMINATION OF NUMBER-AVERAGE DEGREE OF POLYMERIZATION AND MOLAR-BASED DISTRIBUTION OF AMYLOSE BY FLUORESCENT LABELING WITH 2-AMINOPYRIDINE

Suitable conditions for the fluorescent labeling of the reducing resid ue of amylose with 2-aminopyridine were examined. Amylose of up to 38. 5 nmol was labeled with a constant labeling efficiency. The same effic iencies were obtained for amyloses having a number-average degree of p olymerization (dp(n)) of 521-4400. The analysis of labeled amylose on size-exclusion HPLC with refractive index and fluorescence detection e nabled the determination of dp(n) and dp distribution on a molar basis . The analysis of eight amylose specimens from seven botanical sources (potato, sweet potato, barley, wheat, indica rice, japonica rice, and maize) gave dp(n) values in good agreement with those determined by a conventional colorimetric method. The molar-based distributions of th ese amyloses were characteristic of botanical source and revealed the presence of several molecular species with different dp not detectable in the distribution on a weight basis. Small amyloses with a dp less than 10(3) were predominant in the cereals while amyloses with a dp ov er 10(3) were predominant in the tubers, suggesting a difference in th e biosynthetic process determining the dp distribution of amylose betw een cereals and tubers. (C) 1998 Elsevier Science Ltd. All rights rese rved.