dc.contributor.advisor |
Quek, SY |
en |
dc.contributor.advisor |
McGillivray, D |
en |
dc.contributor.author |
Guo, Yuexia |
en |
dc.date.accessioned |
2011-02-27T20:38:10Z |
en |
dc.date.issued |
2011 |
en |
dc.identifier.uri |
http://hdl.handle.net/2292/6486 |
en |
dc.description |
Full text is available to authenticated members of The University of Auckland only. |
en |
dc.description.abstract |
Astaxanthin is an important carotenoid that exhibits a high antioxidant activity in humans. However, this compound has low stability in light and high temperature as well as limited solubility in an aqueous medium, contributing to low bioavailability in humans. Liposomes, which are composed of phospholipids, are widely used as a coating material in the pharmaceutical and food industry as an encapsulating technique. The objectives of this research were to encapsulate astaxanthin by liposomes and to determine the optimum formulation. The characteristics of liposomes and astaxanthin including concentration of entrapped astaxanthin, encapsulation efficiency, liposome size and size distribution as well as stability were studied. The interaction between astaxanthin and liposome bilayers was also investigated. The liposomes used in this study were prepared from egg yolk phosphatidylcholine with different ratios of astaxanthin and cholesterol using the lipid film hydration followed by the extrusion method. Transmission electron microscopy (TEM) and dynamic light scattering technique were used to confirm the formation of the liposomes, and to measure the size and size distribution of liposomes. Spectrophotometry was used to detect the concentration of entrapped astaxanthin in the liposomes. Fluorescence spectrophotometry was employed to study the permeability of the liposomes and Fourier transform infrared spectroscopy (FTIR) was used to study the interation between astaxanthin and lipid bilayers. The results show that the extrusion method can produce a homogeneous liposome suspension with a defined particle size. Both size and size distribution of liposomes were affected by the extrusion method and initial astaxanthin concentration. Increasing the number of passes through the membrane in the extruder decreased the diameter and polydispersity of the liposomes. The solubility of astaxanthin was appearantly enhanced by liposomal encapsulation. Both the concentration of the entrapped astaxanthin and encapsulation efficiency in the aqueous medium were affected by the initial concentration of astaxanthin used in the formulation, the presence of cholesterol and the pore size of the membrane used during extrusion process. The highest encapsulation efficiency (86.15%) and concentration of entrapped astaxanthin (68.92 ug/ml) in the liposome suspension were achieved at ii the formulation of asataxathin: cholesterol: phosphatidylcholine = 4:0:100 (in molar ratio) using a 200 nm pore size membrane. Result also shows that liposomal encapsulation can increase the stability of astaxanthin during heating at 60⁰ C but it cannot enchance the stability of astaxanthin under the storage in UV-light. FTIR confirmed that astaxanthin was entrapped in the liposomes and thus influenced the lipid membrane structure. The FTIR spectra showed that the astaxanthin had a strong interaction with the phosphate headgroups of the phosphatidylcholines but had no apparent effects on the alkyl chains of the phosphatidylcholine. |
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dc.publisher |
ResearchSpace@Auckland |
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dc.relation.ispartof |
Masters Thesis - University of Auckland |
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dc.relation.isreferencedby |
UoA99212894514002091 |
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dc.rights |
Restricted Item. Available to authenticated members of The University of Auckland. |
en |
dc.rights.uri |
https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm |
en |
dc.title |
Liposomal encapsulation of astaxanthin |
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dc.type |
Thesis |
en |
thesis.degree.discipline |
Food Science |
en |
thesis.degree.grantor |
The University of Auckland |
en |
thesis.degree.level |
Masters |
en |
dc.rights.holder |
Copyright: the author |
en |
pubs.elements-id |
206607 |
en |
pubs.record-created-at-source-date |
2011-02-28 |
en |
dc.identifier.wikidata |
Q112886400 |
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