Detection of Free Radicals in Beer Oxidation

Abstract

ReagentsShort-lived radicals produced during the incubation of beer at 60°C were detected by electron spin resonance (ESR) spectroscopic analysis using N-teti-butyl-cY-phenylnitrone (PBN) as a spin trapping reagent. The hyperfine splitting (hfs) constants were 15.7 f 0.2 G and 3.2 t 0.2 G for 01~ and a!, respectively. The hfs constants of PBN adducts produced by Coho y irradiation were 15.6 rf: 0.3 G and 3.1 -C 0.2 G for on and CY~ in beer and 15.7 f 0.3 G and 3.3 of: 0.3 G for on and c$r in double distilled water. It is proposed, therefore, that short-lived radicals produced during the incubation of beer at 60°C may be hydroxyl radicals.

The role of lager beer yeast in oxidative stability of model beer

“…The oxidation of flavour compounds in wort and/or beer is initiated by the reaction of oxygen with transition metals, such as iron and copper, thus generating the superoxide anion (), which may be further reduced and protonated to hydrogen peroxide (H 2 O 2 ). The superoxide anion and hydrogen peroxide can then undergo the Haber–Weiss and Fenton reactions, respectively, with iron and/or copper ions to produce the very reactive hydroxyl radical (OH ˙ ) (Kaneda et al. 1988).…”

Behavior and role of iron ions in beer deterioration

“…As cited in the Introduction, it has been shown that active oxygens such as superoxide (02-), hydrogen peroxide (HzOz), and the hydroxyl radical ('OH) are produced during the process of beer oxidation (Kaneda et al, 1988(Kaneda et al, , 1989(Kaneda et al, ,1990(Kaneda et al, ,1991. The active oxygens attack several beer components and initiate a series of free-radical reactions, leading to beer staling.…”

The Peroxide Challenge Test: A Novel Method for Holistic Near-Real Time Measurement of Beer Flavour Stability

“…Thus, it can be expected that a beer with a longer ESR lag time will be more flavour stable than a beer with a shorter ESR lag time. Furthermore, the specificity and intensity of the ESR signal after 150 minutes of forced aging at 60°C was reported to give an indication of the intensity of the aged character, the extent of the oxidative processes and the rate of radical formation after exhaustion of the antioxidant potential and the onset of beer staling 10,11,29 . An example of a typical ESR graph for a "standard" rated beer and for a "reject" rated beer is shown in Fig.…”

“…ESR is now widely used to detect ROS in the context of beer aging. Although a number of beer radicals are presumed to be involved in flavour staling, only one reactive oxygen species -the 1-hydroxyethyl radical is probably directly measured by ESR 1,10,11,29 . Developments like those above will extend the usefulness of this approach 25 .…”

“…As a consequence, a holistic approach has to be taken to reliably measure and predict beer staling. Currently, one of the most holistic analysis techniques for predicting flavour stability is electron spin resonance (ESR) 1,10,11,29 .…”