Abstract

Starch is a staple food in human and animal diets, but also a raw material widely used for industrial purposes. By genetical modification of starch-synthesising enzymes in crop plants, starch yields could be increased and novel starches with particular qualities could be produced for industrial use. However, the process of starch biosynthesis and its regulation is still not completely understood. One of the major groups of enzymes in starch biosynthesis is the starch branching enzymes (SBEs), which introduce the branch points into amylopectin. This thesis describes some properties of two different families of SBEs from potato and barley. In addition, starch structure from both developing and mature barley has been characterised. Initially, a linear substrate for in vitro studies of SBEI and SBEII from potato was prepared. The linear dextrins were produced by enzymatic hyrdolysis of retrograded starch and then further fractionated through ethanol precipitation. The in vitro branching properties of SBEI and SBEII from potato were examined using iodine-staining, NMR spectroscopy, chromatographic and enzymatic methods. The two enzyme isoforms showed different substrate specificities and the branched products exhibited different chain length distribution profiles, but a similar degree of branching. In develping barley, starch structure and the expression of the gene encoding for barley SBEI were examined. The amylose content increased during development and followed a time course similar to that of the expression of the SBEI gene. The amylopectin chain length distribution was examined in the later stages of development, but no changes in the amylopectin structure were observed. In mature waxy barley, the amylose content and amylopectin structure in different parts of the grain were analysed. It was shown that the amylose content was signigicantly higher in the peripheral parts of the endosperm than in the centre, whereas the amylopectin chain length distribution was similar in all parts of the endosperm.

Keywords

barley; potato; amylose; amylopectin; Hordeum vulgare L.; Solanum tuberosum L.; starch branching enzyme; starch biosynthesis

Published in

Acta Universitatis Agriculturae Sueciae. Agraria
2001, number: 287
ISBN: 91-576-5834-X
Publisher: Swedish University of Agricultural Sciences

SLU Authors

• Andersson, Lena

  • Department of Molecular Sciences, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Food Science


Permanent link to this page (URI)

https://res.slu.se/id/publ/107652