Structures of rice amylopectins with low and high affinities for iodine

The amylopectins from the apparent low- (japonica) and high-amylose (indica) varieties of rice showed, respectively, low (0.39–0.87 g/100 g) and high (1.62–2.57 g/100 g) affinities for iodine, average chain-lengths (c.l.) of 19–20 and 21–22, and similar beta-amylolysis limits (56–59%). Gel filtration of the isoamylase-debranched amylopectins indicated that the amylopectins showing a high affinity for iodine contained lower proportions of short chains and higher proportions (up to 14.2%) of the long chains (c.l., 85–180). The long chains appeared to be derived from long B-chains with side chains widely spaced and located far from the non-reducing terminus. The apparent high-amylose (30–32%) rice starches had ordinary contents (15.5–18.5%) of amylose.