SIZE DISTRIBUTIONS OF AMYLOSE AND AMYLOPECTIN SOLUBILIZED FROM CORN STARCH GRANULES

Size distributions of extracts derived from starch were investigated t o aid in elucidating structure-function relationships of these polymer s in water. Starch granules derived from waxy maize and amylomaize VII were dissolved in water by microwave heating in a high pressure vesse l. Transmission electron microscopy of starch deposited from dilute so lution and rotary shadowed with platinum, revealed that amylopectin im aged 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 amy lopectin components ranged from about 37 to 980 nm whereas the diamete r of circular amylopectin components ranged from about 44 to 200 nm. A lthough 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 ra nged from about 46 to 254 nm. After smoothing and curve fitting, we fo und that all size distributions investigated could be treated as if th ey 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.