A Kinetic Study on the Isomerization of Hop α-Acids

• Published in: Journal of agricultural and food chemistry 2008-08, Vol.56 (15), p.6408-6415
• Main Authors: Jaskula, Barbara, Kafarski, Pawel, Aerts, Guido, De Cooman, Luc
• Format: Article
• Language: English
• Subjects: activation energy; alpha-acids; Beers; Biological and medical sciences; boiling; brewing; Chemical Changes Induced by Processing/Storage; Cyclohexenes - analysis; Cyclohexenes - chemistry; Fermented food industries; food composition; Food industries; food matrix; Fundamental and applied biological sciences. Psychology; Hop α-acids; hops; Hot Temperature; Humulus - chemistry; Isomerism; isomerization; isomerization yield; isomers; Kinetics; rate constant; reaction kinetics; Solutions; temperature; Terpenes - analysis; Terpenes - chemistry; Thermodynamics; trans-/cis-iso-α-acids; wort (brewing)
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf8004965

In this article, a detailed study on hop α-acid isomerization kinetics is presented. Because of the complex wort matrix and interfering interactions occurring during real wort boiling (i.e., trub formation and α-acids/iso-α-acids complexation), this investigation on α-acid isomerization kinetics was performed in aqueous buffer solution as a function of time (0−90 min) and heating temperature (80−100 °C). Rate constants and activation energies for the formation of individual iso-α-acids were determined. It was found that iso-α-acid formation follows first-order kinetics and Arrhenius behavior. Differences in activation energies for the formation of trans- and cis-isomers were noticed, the activation energy for the formation of trans-iso-α-acids being approximately 9 kJmol−1 lower.