Enzymatic acylation of starch

The possibility of enzyme catalysed synthesis of starch esters, is an extremely interesting prospect, as a new route for synthesis of biodegradable polymers from renewable material, through mild processes. Starch esters have traditionally been analysed by saponification and back-titration, however this method was found to be unreliable. Quantification through integration of 1H-NMR peaks, was also found problematic for low degrees of substitution (DS, mol acyl group per mol anhydroglucose). Therefore an analytical scheme employing alkaline methanolysis of starch esters and analysis of the resulting methyl esters by GC/FID is presented. This technique is employed for starch esters with fatty acids of medium chain length and can be suitably modified to accommodate other chain lengths. Lipase catalysed synthesis of starch esters with decanoic acid was performed in concentrated aqueous systems, where the starch is gelatinised prior to enzymatic reaction. The reaction showed a pronounced optimal water content (1.25 mL of water for gelatinisation per g of starch), in which the equilibrium was sufficiently shifted, in order to produce starch acylated to a useful extent (0.018 DS). Use of fatty acids with other groups on their alkyl chains, as substrates, led to successful synthesis of starch 10-undecynoate. The triple bond in the -position of the fatty acid may act as a grafting site for further modification, with azide containing molecules, through "click" reactions (dipolar cycloaddition). Investigation of other reaction systems for enzymatic starch acylation, revealed nonenzymatic transesterification of vinyl decanoate with starch in DMSO. On the other hand, the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]), was a suitable medium for lipase catalysed synthesis of starch esters with decanoic acid (0.016 DS). Treatment with -amylase resulted in decreased hydrolysis for the modified starches, as the acyl groups present inhibited the action of the enzyme. The presence of approximately one acyl group for every one hundred glucose units is sufficient to decrease extent of hydrolysis by 11%.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral-pg

Grantor dc:publisher.institution

University of Strathclyde

Year dc:date.issued

2009

Author dc:creator

• Alissandratos, Apostolos

DOI

10.48730/m4db-sk04

Identifier

T12605

OAI identifier oai:identifier

oai:strathclyde:db78tc035