STRUCTURE OF THE AMYLOPECTIN FRACTION OF AMYLOMAIZE

The amylopectin fraction (Ap-fraction) from three amylomaize starches (amylose content, 36, 41, and 59%) was fractionated into three amylope ctin components (having different molecular size) and a short-chain co mponent by gel-permeation chromatography. The content of the largest a mylopectin component was relatively low in a high-amylose maize starch and it had an iodine affinity (i.a., g/100 g) of 1.94-2.50 and averag e chain length (clBAR) of 29-30. Both values increased with decrease o f molecular size (i.a. < 7.23, clBAR < 41). The proportion of long sid e chains [weight-average dp (dp(w)BAR) 99-110] increased with decrease of molecular size, whereas that of short side chains (dp(w)BAR 17-22) decreased. This is the reason why a smaller component had a larger i. a. and clBAR. Very long (dp(w)BAR 400-690) and medium-size (dp(w)BAR 4 5-48) side chains were present in similar proportions, regardless of m olecular size. The short-chain component was slightly branched (number of chains, 1.9-2.1 on average) and had an i.a. of 8.20-9.57, dp(w)BAR of 120, and number-average dp of 92-95. A large amount of the short-c hain component (27% of the Ap-fraction, by weight) was found in the hi gh-amylose (59%) maize starch.