Reactivity of Beer Bitter Acids Toward the 1-Hydroxyethyl Radical as Probed by Spin-Trapping Electron Paramagnetic Resonance (EPR) and Electrospray Ionization-Tandem Mass Spectrometry (ESI-MS/MS)

Author(s)

de Almeida, Natalia E. C. ^[1] ; Homem-de-Mello, Paula ^[2] ; De Keukeleire, Denis ^[3] ; Cardoso, Daniel R. ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Quim Sao Carlos IQSC, BR-13560970 Sao Carlos, SP - Brazil

^[2] Univ Fed ABC, BR-09210170 Sao Paulo - Brazil

^[3] Univ Ghent, Fac Pharmaceut Sci, B-9000 Ghent - Belgium

• Document type: Journal article
• Source: Journal of Agricultural and Food Chemistry; v. 59, n. 8, p. 4183-4191, APR 27 2011.
• Web of Science Citations: 11

Abstract

The iso-alpha-acids or isohumulones are the major contributors to the bitter taste of beer, and it is well-recognized that they are degraded during beer aging. In particular, the trans-isohumulones seem to be less stable than the cis-isohumulones. The major radical identified in beer is the 1-hydroxyethyl radical; however, the reactivity between this radical and the isohumulones has not been reported until now. Therefore, we studied the reactivity of isohumulones toward the 1-hydroxyethyl radical through a competitive kinetic approach. It was observed that both cis- and trans-isohumulones and dihydroisohumulones are decomposed in the presence of 1-hydroxyethyl radicals, while the reactivities are comparable. On the other hand, the tetrahydroisohumulones did not react with 1-hydroxyethyl radicals. The apparent second-order rate constants for the reactions between the 1-hydroxyethyl radical and these compounds were determined by electron paramagnetic resonance (EPR) spectroscopy and electrospray ionization-tandem mass spectrometry {[}ESI(+)-MS/MS]. It follows that degradation of beer bitter acids is highly influenced by the presence of 1-hydroxyethyl radicals. The reaction products were detected by liquid chromatography electrospray ionization-ion trap-tandem mass spectrometry (LC-ESI-IT-MS/MS), and the formation of oxidized derivatives of the isohumulones was confirmed. These data help to understand the mechanism of beer degradation upon aging. (AU)

• FAPESP's process: 08/08773-0 - Reativity of iso-alpha-acids and its hydrogenated derivatives towards the 1-hydroxyethyl radical: implications in the sensorial quality loss of beer
• Grantee: Natália Ellen Castilho de Almeida
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 09/00858-0 - Mechanism and consequences of redox process in food: Chemical and Photochemical aspects of the oxidative deterioration and antioxidant activity of beer and dairy products
• Grantee: Daniel Rodrigues Cardoso
• Support Opportunities: Regular Research Grants