Date of Award
Doctor of Philosophy
Food Science and Human Nutrition
Structures and properties of starches isolated from waxy, amylose-reduced (Kanto 107), and normal hard-red-winter wheat (Centura and a commercial product) grains were characterized. The absence of amylose (AM) in waxy wheat starch did not affect crystalline pattern (A-type), granule size and morphology, and gelatinization temperature, but increased the degree of crystallinity and changed pasting properties. Differences in pasting temperatures and peak viscosities between waxy and normal wheat starches were substantially greater than the differences between maize starch counterparts.;The weight-average molecular weight (MW) of the wheat amylopectin (AP) displayed a negative correlation with AM content, whereas the proportion of extralong branch-chains of wheat AP were positively correlated with AM content. The MW of APs varied from 7.0 x 107 to 5.7 x 109, depending on botanical source. The APs of waxy starches had larger MW and, in general, larger dispersed molecular densities than did those of normal AP counterparts. Waxy wheat AP did not contain extra-long chains (ELC) that were synthesized progressively by granule-bound starch synthase I (GBSSI) in normal wheat AP. These results suggested that the APs of waxy starches carried more branch-chains but no ELCs, which resulted in more densely packed molecules than did those of normal AP counterparts. Different branch structures between APs of A- and B-type starches resulted in different dispersed molecular densities in dilute solutions. The APs of B-type starches had much longer but fewer branch-chains, which resulted in smaller dispersed molecular densities compared with the A-type APs.;Individual glycogen synthases (GSI and II) and glycogen branching enzyme (GBE) of cyanobacterium Synechocystis sp. PCC6803 were insertionally mutagenized by homologous recombination. Branch chain-length distributions of glycogens produced by GSI- and GSII - mutants were different from each other. Prominent increases in intermediate-size chains (DP8-18) were observed in glycogen of the GSI - mutant compared with those of the wild-type and the GSII - mutant. The results indicated that the two GS isoforms had different specificities on glycogen structure. Because of the GBE deficiency, GBE- mutant strain produced less glucan that had negligible branch-linkages and was water-insoluble. The GBE increased overall rate of glycogen biosynthesis in cyanobacterium.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
Yoo, Sang-Ho, "Structures, properties, and biogenesis of starch and cyanobacterial glycogen " (2001). Retrospective Theses and Dissertations. 1093.