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On the Reaction of Lupulones, Hops β-acids, with 1-Hydroxyethyl Radical.
MedLine Citation:
PMID:  23031058     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Lupulones, hops β-acids, are one of the main constituents of the hops resin and have an important contribution to the overall bacteriostatic activity of hops during beer brewing. The use of lupulones as natural alternatives to antibiotics is increasing in the food industry and also in the bio-ethanol production. However, lupulones are easy oxidizable and have been shown to be very reactive towards 1-hydroxyethyl radical with apparent bimolecular rate constants close to diffusion control k = 2.9x108 and 2.6x108 L mol-1s-1 at 25.0 ± 0.2 oC in ethanol-water solution (10% of ethanol (v/v)) as probed by EPR and ESI-IT-MS/MS spin-trapping competitive kinetics, respectively. The free energy change for an electron-transfer mechanism is ΔGo = 106 kJ/mol as calculated from the oxidation peak potential experimentally determined for lupulones (1.1 V vs. NHE) by cyclic voltammetry and the reported reduction potential for 1-hydroxyethyl radical. The major reaction products identified by LC-ESI-IT-MS/MS and ultrahigh resolution accurate mass spectrometry (orbitrap FT-MS) are hydroxylated lupulone derivatives and 1-hydroxyethyl radical adducts. The lack of pH-dependence for the reaction rate constant, the calculated free energy change for electron-transfer, and the main reaction products strongly suggest the prenyl side chains at the hops β-acids as the reaction centers rather than the β,β'-triketone moiety.
Authors:
Natália E C de Almeida; Eduardo S P Nascimento; Daniel Rodrigues Cardoso
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-10-3
Journal Detail:
Title:  Journal of agricultural and food chemistry     Volume:  -     ISSN:  1520-5118     ISO Abbreviation:  J. Agric. Food Chem.     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-10-3     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0374755     Medline TA:  J Agric Food Chem     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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