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Title: Novel processes for extraction and fractionation of fatty acids from microbial cell mass
Author: Miranda, Andreia Manuela Martins
ISNI:       0000 0004 5917 5147
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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In this thesis a novel integrated process for extraction and fractionation of long chain polyunsaturated fatty acids (LC-PUFA), particularly the high-value docosahexaenoic acid (DHA), from wet microbial cell mass was investigated. The research was focused in two main aspects: (i) selection of enzymes for stepwise hydrolysis of triacylglycerols present the cell mass, and (ii) evaluation of a biphasic membrane contactor system, comprising an asymmetric membrane, for extraction of released fatty acids. The kinetics of hydrolysis of triacylglycerols to diacylglycerols, monoacylglycerols and free fatty acids for specific and non-specific lipases was characterised. It was demonstrated that the enzymatic hydrolysis of triacylglycerols can be effectively performed directly in the cell mass suspension, i.e. without previous isolation of the lipid fraction. New analytical methods were developed for the analyses of acylglycerols and fatty acids by LC-ESI-MS. The access to the concentration profiles of tri-, di-, and monoacylglycerols throughout the reaction enabled a better evaluation of the performance of enzymes tested in terms of kinetics and selectivity. An effective selective hydrolysis can be attained by employing specific and non-specific lipases in the enzymatic hydrolysis of triacylglycerols. Based on the results obtained, optimum combinations of enzymes for process applications can be proposed. Asymmetric polyimide membranes were prepared and tested for the separation of fatty acids in the biphasic membrane contactor system. It was found that the type of polymer, the membrane molecular weight cut-off, and the composition of the aqueous phase all had considerable effect on mass transfer across the membrane. Significantly higher mass transfer coefficients of long-chain fatty acids than previously reported were achieved. The solute transport mechanism through asymmetric polyimide porous membranes in the biphasic system was also explored. However, the membrane mass transfer coefficients calculated based on the solute transport model proposed, did not explain experimental observations well. The feasibility of the proposed integrated process for sequential enzymatic hydrolysis of triacylglycerols and simultaneous separation of released fatty acids was demonstrated. As expected, the presence of an emulsion in the aqueous phase limited the mass transfer through the membrane. However, promising results were observed, and mass transfer rates may be improved by further optimisation of the operating conditions. It is then concluded that the objective of the present work was accomplished as a partial fractionation of the main fatty acids was obtained.
Supervisor: Livingston, Andrew ; Aasen, Inga Sponsor: European Commission ; Norges forskningsra╠Őd
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available