Section 10
Chapter 9,260

Properties of damaged starch granules: IV. Composition of ball-milled wheat starches and of fractions obtained on hydration

Morrison, W.R.; Tester, R.F.

Journal of Cereal Science 20(1): 69-77


ISSN/ISBN: 0733-5210
DOI: 10.1006/jcrs.1994.1046
Accession: 009259687

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Wheat starches were ball milled to obtain various levels of damaged starch. Amylose was affected only after severe milling, when there were changes indicating slight depolymerization. Some amylopectin (AP) was converted to low molecular weight fragments (LMWAP) at all levels of damage, and molecular size tended to decrease with increasing milling time, indicating further breakdown of LMWAP. On hydration, damaged starch formed gel and soluble material, leaving native (undamaged) granules and birefringent remnants of partially damaged granules. The content of soluble material increased with damaged starch content, but gel content only increased to c. 60%, then declined slightly as it was converted to soluble material. The gel contained mostly AP with a little LMWAP, nearly all of the lipid-complexed amylose of the damaged starch, and much of the free amylose. Soluble material contained about 10% lipid-free amylose and 90% LMWAP, with traces of AP and lipid-complexed amylose only at high levels of damaged starch. The cold water extract from four millstreams (3.6-10.6% damaged starch) was very similar to soluble material from ball-milled starches. It is suggested that LMWAP is formed by shearing glycosidic bonds in B-2, B-3 and B-4 internal chain segments of amylopectin (between clusters of double helices formed by external chains) on the reducing side of alpha-1,6-branch points.

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