On the Reaction of Lupulones, Hops beta-Acids, with 1-Hydroxyethyl Radical

Autor(es)

de Almeida, Natalia E. C. ^[1] ; do Nascimento, Eduardo S. P. ^[1] ; Cardoso, Daniel R. ^[1]

Afiliação do(s) autor(es)

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

• Tipo de documento: Artigo Científico
• Fonte: Journal of Agricultural and Food Chemistry; v. 60, n. 42, p. 10649-10656, OCT 24 2012.
• Citações Web of Science: 9

Resumo

Lupulones, hops beta-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 bioethanol production. However, lupulones are easy oxidizable and have been shown to be very reactive toward 1-hydroxyethyl radical with apparent bimolecular rate constants close to diffusion control k = 2.9 x 10(8) and 2.6 x 10(8) L mol(-1) s(-1) at 25.0 +/- 0.2 degrees C 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 Delta G degrees = 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 beta-acids as the reaction centers rather than the beta,beta'-triketone moiety. (AU)

• Processo FAPESP: 11/09273-4 - Reatividade de terpenos e flavonoides prenilados frente a radicais formados durante o envelhecimento da cerveja
• Beneficiário: Natália Ellen Castilho de Almeida
• Modalidade de apoio: Bolsas no Brasil - Doutorado
• Processo FAPESP: 11/51555-7 - Pão e carne para o futuro
• Beneficiário: Daniel Rodrigues Cardoso
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 09/54040-8 - EMU: aquisição de um espectrômetro de massas de alta resolução Orbitrap para descoberta e elucidação estrutural compostos biologicamente ativos: aplicações em proteômica e biomarcadores, síntese, isolamento e caracterização de produtos naturais, estudos de sistemas redox em alimentos e síntese enzimática
• Beneficiário: Emanuel Carrilho
• Modalidade de apoio: Auxílio à Pesquisa - Programa Equipamentos Multiusuários