SIZE DISTRIBUTIONS OF AMYLOSE AND AMYLOPECTIN SOLUBILIZED FROM CORN STARCH GRANULES

Size distributions of extracts derived from starch were investigated to aid in elucidating structure-function relationships of these polymers in water. Starch granules derived from waxy maize and amylomaize VII were dissolved in water by microwave heating in a high pressure vessel. Transmission electron microscopy of starch deposited from dilute solution and rotary shadowed with platinum, revealed that amylopectin imaged from waxy maize could be broadly classified as about 28% circular space filling patches containing branched clusters and 72% asymmetric linear containing branched clusters. Lengths of asymmetric linear amylopectin components ranged from about 37 to 980 nm whereas the diameter of circular amylopectin components ranged from about 44 to 200 nm. Although the starch in amylomaize VII is about 70% amylose, its narrow asymmetric structure when visualized by microscopy enabled us to image amylose even though amylopectin was present. Lengths of components ranged from about 46 to 254 nm. After smoothing and curve fitting, we found that all size distributions investigated could be treated as if they were multimodal in nature. The most abundant amylose component had a linear density of 8.2 x 10(3) molar mass units/nm. This value could be explained if amylose had an aggregation number of about 5.9.