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Issue 5, 2005
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Fate of flavins in sensitized photodegradation of isohumulones and reduced derivatives: studies on formation of radicals viaEPR combined with detailed product analyses

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Abstract

Photodegradation of isohumulones accounts for formation of the lightstruck flavor in beer. The reactions involved are mediated by riboflavin, a natural photosensitizer present in beer in ppb quantities. The results of an investigation of this sensitized degradation process are presented herein. Product analyses and electron paramagnetic resonance spectroscopy, in steady-state as well as in time-resolved mode, offer extensive insight into the photophysical and photochemical details of the degradation mechanism. In contrast to energy transfer and Norrish type I α-cleavage reactions that take place on direct irradiation of isohumulones, the sensitization pathway proceeds via one-electron redox chemistry involving the excited triplet state of riboflavin and derivatives. The flavin semiquinone radical thus formed could be readily detected, either by steady state or by time-resolved electron paramagnetic resonance spectroscopy. Superimposed signals in the spectra revealed the presence of radical fragments derived from isohumulones or tetrahydroisohumulones, which, on recombination with riboflavin semiquinone radicals, produced stable reaction products that were identified by HPLC-MS. However, no superimposed signals were observed on sensitized irradiation of dihydroisohumulones.

Graphical abstract: Fate of flavins in sensitized photodegradation of isohumulones and reduced derivatives: studies on formation of radicals via EPR combined with detailed product analyses

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Article information


Submitted
07 Jan 2005
Accepted
10 Mar 2005
First published
22 Mar 2005

Photochem. Photobiol. Sci., 2005,4, 412-419
Article type
Paper

Fate of flavins in sensitized photodegradation of isohumulones and reduced derivatives: studies on formation of radicals via EPR combined with detailed product analyses

A. Heyerick, K. Huvaere, D. De Keukeleire and M. D. E. Forbes, Photochem. Photobiol. Sci., 2005, 4, 412
DOI: 10.1039/B500285K

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