ascorbic-acid and dimethyl-sulfide

During malt kilning, dimethyl sulfide (DMS) is partly oxidized to dimethyl sulfoxide (DMSO), which can be reduced by yeast to generate DMS during fermentation. The aim of this study was to test the effect of malt-derived potential antioxidants on DMS oxidation and to assess their applicability for DMSO minimization. In the presence of 18 μM copper, all tested antioxidants (250 μM) catalyzed DMS oxidation to deviating extents (sulfite > ascorbic acid (Asco) > gallic acid (GA) > L-cysteine (Cys) > L-glutathione (GSH)). Hydrogen peroxide was found as primary DMS oxidant for each substance except for sulfite. Electron spin resonance spectroscopy provided evidence for the formation of bisulfite radicals and peroxymonosulfate radicals, which are proposed as being capable of exhaustive DMS oxidation (∼100%) over a wide concentration. The data demonstrate that use of antioxidants per se cannot be suggested for the minimization of DMSO formation in malt and other foodstuffs. Potential shifts from pro- to antioxidative behavior of antioxidants and their implications on malt quality are discussed.

Topics: Antioxidants; Ascorbic Acid; Copper; Cysteine; Edible Grain; Electron Spin Resonance Spectroscopy; Food Handling; Gallic Acid; Glutathione; Hydrogen Peroxide; Oxidation-Reduction; Sulfides

A method for the simultaneous measurement of volatile sulfur compounds (COS, H2S, CS2, CH3SH, DMS) is established with preconcentration and GC-flame photometric detection (FPD). Prior to preconcentration of ambient air, it was necessary to remove SO2, water vapor and atmospheric oxidant. SO2 and water vapor were removed using a glass fiber filter and a cooled PTFE water trap loop, respectively. In order to remove atmospheric oxidant, the efficiency of an ascorbic acid scrubber was examined. It was found that an ascorbic acid scrubber enabled measurement of volatile sulfur compounds without adsorption and reaction loss. The detection limits for COS, H2S, CS2, CH3SH and DMS were 20, 34, 35, 263 and 44 pg of S, respectively.

Topics: Air; Antioxidants; Ascorbic Acid; Carbon Disulfide; Chromatography, Gas; Hydrogen Sulfide; Ozone; Sulfhydryl Compounds; Sulfides; Sulfur Compounds; Sulfur Dioxide; Sulfur Oxides; Volatilization