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Lecture Dragica Jakovljevic

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WanneerWaar
27 april 2007 FWN-Building 5118.-156, Nijenborgh 4, 9747 AG, Groningen
Speaker: Dr. Dragica Jakovljevic
Affiliation: ICTM Center for chemistry, Belgrade, Serbia
Title: Structural characterization of pullulan produced by Aureobasidium pullulans
Date: Fri Apr 27, 2007
Start: 11.00
Location: FWN-Building 5118.-156
Host: Katja Loos
Telephone: +31 50 363 6867

Abstract

Pullulan is a linear homopolysaccharide of glucose, which is produced as water soluble, extracellular polysaccharide by certain strain of the polymorphic fungus Aureobasidium pullulans. Due to adhesive properties, it can be used to form fibers, compression moldings and strong, oxygen-impermeable films. Pullulan and its derivatives have numerous potential in food, pharmaceutical, and industrial applications.

Structural characterization of isolated and purified pullulan, produced by Aureobasidium pullulans, strain CH-1 (IChTM, Collection of Microorganisms, Belgrade) was performed by using standard analitycal methods: gel-permeation chromatography, methylation analysis combined with GLC and GC-MS, enzymatic hydrolysis and spectral techniques (FTIR, 13C- and 1H-NMR).

It was established that pullulan is an alpha-D-glucan with a linear structure wherein maltotriose units, i. e., units of three alpha-D-1,4-linked glucose molecules, are repeatedly polymerised via alpha-D-1,6 linkages on the terminal glucose residues. It is possible that pullulan contains additional structural features, perhaps depending on culture conditions and strain differences. In the enzymatic hydrolysis of pullulan, a certain amount of a higher oligosaccharide, most frequently with maltotetraosyl residues, was observed in addition to the predominant maltotriose subunits.

Using the susceptibility of pullulan CH-1 to hydrolysis catalysed by porcine alpha-amylase, the polysaccharide was cleaved and the fragments obtained fractionated by gel-permeation chromatography. The heterogenous size of the fragments indicates that there is no apparent regular distribution of tetrasaccharide units in the pullulan chain. Enzymatic digestion of pullulan CH-1 using pullulanase, followed by gel-permeation chromatography of the resulting digest confirmed these results as did preparative paper chromatography and CI mass spectrometry of the separated components, i. that maltotetraosyl units are distributed throughout the molecule of pullulan CH-1. This indicated that maltotetraose (about 7%) was an integral part of the pullulan chain and was replacing maltotriose residues in some positions to form alpha-(l-6)-glucosidic linkages on the terminal glucose residues without affecting the linearity of the pullulan molecule. This unique linkage pattern endows pullulan with distinctive physical traits. Recently, it was reported that pullulan CH-1 sensitized with chromium ions posses promising holographic properties.

Laatst gewijzigd:22 oktober 2012 14:30