Studies of iso-alpha-acids: analysis, purification, and stability.

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Studies of iso-alpha-acids: analysis, purification, and stability.

Type: Doctoral Thesis
Title: Studies of iso-alpha-acids: analysis, purification, and stability.
Author: Khatib, Alfi
Publisher: Div. of Pharmacognosy, Institute of Biology Faculty of Mathematics and Natural Sciences, Leiden University
Issue Date: 2006-10-10
Keywords: Hop
High Performance Liquid Chromatography
Nuclear Magnetic Resonance
Multivariate data analysis
Abstract: The female cones of hop (Humulus lupulus L.) are added to beer, providing taste and flavour and contributing to the stability of foam. The main constituents of hop related to these properties are generically known as alpha-acids. During the brewing process, these acids are isomerized, resulting in the formation of three pairs of trans-/cis-iso-alpha–acids. The aim of this thesis project was to develop a method for the analysis (Chapter 2 and 7) as well as the purification of iso-alpha-acids (Chapter 3-5). Moreover, the stability of iso-α-acids need to be improved (Chapter 6) since these compounds degrade easily in the light and in the presence of oxygen. We have shown that β-CD is effective to separate cis-isomers from trans-isomers and at the same time increases the stability of the complexed compounds. The pure individual iso-alpha-acids can now be produced from pure alpha-acids, obtained from a CPC separation, followed by isomerization and beta-CD separation of the two isomers. These compounds can be used as reference standard for analytical purposes to replace the DCHA-salts of trans-iso-alpha-acids. It also opens the possibility to use pure iso-alpha-acids in brewery research. An HPLC system using these pure individual iso-alpha-acids as calibration standard was developed as well. The application of 2D J resolved NMR has been developed and seems promising to detect a wide range of compounds in beer.
Description: Promotor: R. Verpoorte, Referent: P.S. Hughes
With Summary in Dutch
Faculty: Faculteit der Wiskunde en Natuurwetenschappen
Citation: Khatib, A., 2006, Doctoral thesis, Leiden University
ISBN: 9090209794
Sponsor: - Committee of Phytochemical Society of Europe Joint Meeting 1999 Fund, the Netherlands. - Dutch Education: Learning at Top Level Abroad (DELTA) scholarship from Leiden University, the Netherlands.

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application/pdf Propositions 19.73Kb View/Open
application/pdf Acknowledgements 20.29Kb View/Open
application/pdf List of Publications 32.20Kb View/Open
application/pdf Curriculum Vitae 18.04Kb View/Open
application/pdf Summary in Dutch 66.82Kb View/Open
application/pdf Summary in English 63.53Kb View/Open
application/pdf Chapter 7 373.1Kb View/Open
application/pdf Chapter 6 159.9Kb View/Open
application/pdf Chapter 5 138.3Kb View/Open
application/pdf Chapter 4 113.0Kb View/Open
application/pdf Chapter 3 165.4Kb View/Open
application/pdf Chapter 2 127.4Kb View/Open
application/pdf Chapter 1 158.8Kb View/Open
application/pdf Title page_ Contents 52.33Kb View/Open
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