Interactions of Phenolics with Reductive Sulfur Compounds and the Oxygen Consumption of Oak Chips

Abstract

Volatile sulfur-containing compounds can react with oxidised phenolics leading to loss of aroma in wine. The primary research question in this thesis was to explore the interactions between individual reductive sulfur compounds and various phenolics in a model wine solution with added catalytic metals through 60 days at 35⁰. The current study focused on three phenolics (caffeic acid, (+)-catechin and quercetin) and five reductive sulfur compounds (hydrogen sulfide, methanethiol, 3-methylthio-1-propanol, dimethyl sulfide and diethyl disulfide). Evolution of phenolics and reductive sulfur compounds were monitored using reverse-phase high performance liquid chromatography (HPLC) coupled with diode array detector and headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry, respectively. The newly formed HPLC peaks were analysed by the combination of solid phase extraction and mass spectrometry. The results of the current study showed an accelerated degradation in solutions containing a mixture of a phenolic (caffeic acid and (+)-catechin) and a simple thiol (hydrogen sulfide and methanethiol) over the first 14 days of incubation. Caffeic acid and (+)-catechin showed to have a protective effect against the degradation of 3-methylthio-1-propanol, dimethyl sulfide and diethyl disulfide. Quercetin showed to have a protective effect against the degradation of reductive sulfur compounds. Based on the mass spectral data, no evidence for phenolic-reductive sulfur adduct was seen. Addition of reductive sulfur compounds, except methanethiol significantly enhanced the 420 nm absorbances in the solutions containing phenolics. The results suggested that addition of phenolics may not be a means of eliminating reductive sulfur compounds from wine. Oak has been shown to consume oxygen during wine aging. The second research question of this thesis was to investigate the oxygen consumption ability by various dosages of French medium toasted oak. For this purpose an oxygen saturated model wine solution was used and the effect of oak dosage on the dissolved oxygen was monitored using an Orbisphere over 250 hours at 16⁰. The current results confirmed the oxygen consumption ability of oak, and also suggested that more than one mechanism may be involved in oxygen consumption by oak. The results may allow the winemakers to better manipulate the use of oak and control the level of aeration during red wine aging.