Glutathione
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GSH is produced by S. cerevisiae during fermentation and can react with a series of reactive oxygen free radicals and maintain the redox balance of S. cerevisiae. With increasing GSH content, the AOX of beer is significantly improved.
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Glutathione is naturally present in grape juice (∼1.3 to 102 mg/L) and can also be synthesized by yeast through the Sulfate Assimilation Pathway. The addition of glutathione to grape juice has been observed to increase H2S production.[1] The mechanism is not yet fully understood but it is generally assumed that glutathione is first hydrolyzed to cysteine, which is then degraded by cysteine desulfhydrase to release H2S under nitrogen-limited conditions.[1]
Final wine concentration of glutathione was correlated with both total N and organic nitrogen.[2] (see http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.913.1799&rep=rep1&type=pdf)
In plant cells, glutathione is the predominant nonprotein thiol and functions primarily as a reducing agent to maintain SH groups in a reduced state (24). Glutathione may occur endogenously in malt flour in the free reduced glutathione (GSH) and free oxidized glutathione disulfide (GSSG) forms as well as in the form of protein-glutathione mixed disulfides (PSSG). The redox status of the various forms of glutathione in grain can undergo considerable changes in response to exogenous factors, for example, temperature (25). GSH is the major water-soluble intracellular antioxidant that resists heat treatment, although its content decreases 50% in barley (26).[3]
Many major antioxidants in living organisms such as bacteria, yeast and humans are rich in thiol activity. One of these is glutathione, a tripeptide, its thiol group is the key for its antioxidant activity [10].[4]
GSH itself is a scavenger of OH• and singlet oxygen and can reactivate certain enzymes that have been inhibited by exposure to high oxygen concentrations (36). However, GSH can interact with H2O2 and iron to produce hydroxyl ions.[5]
Although sulfur dioxide is efficient in its protective role against the oxidation of white wine, there are certain consumers that are sensitive to this antioxidant (11). With this in mind, the tripeptide glutathione has shown some potential to assist sulfur dioxide in its role as an antioxidant. Indeed, glutathione is already known to be capable of performing the main antioxidant reactions of sulfur dioxide although this has not always been in a wine-related matrix (12-17). Glutathione is known to scavenge o-quinone compounds efficiently in wine/juice conditions (Scheme 2) (12, 13). It can react with hydrogen peroxide and undergo addition reactions with aldehyde compounds (14-16), although these reactions have not been studied in wine-like conditions. Cilliers and Singelton (17) examined the oxidation of caffeic acid in the presence of a variety of thiols, including glutathione, and showed a protective effect of the thiols against both caffeic acid loss and oxidative color production. However, this study was in alkaline aqueous solutions, without added ethanol, metal ions or (+)-catechin. All three of these latter components have since been highlighted as critical factors in the oxidative coloration of model wine systems and/or the oxidation reactions of thiol compounds (1, 5, 18-20).[6]
- Wang, B., He, & Zhang. (2014b). Secretion expression of sod1 and its overlapping function with gsh in brewing yeast strain for better flavor and anti-aging ability. Journal of Industrial Microbiology & Biotechnology, 41, 1415–1424.
References[edit]
- ↑ a b Huang, CW., et al. "Hydrogen sulfide and its roles in Saccharomyces cerevisiae in a winemaking context." FEMS Yeast Research. Volume 17, Issue 6, September 2017
- ↑ Park, SK, et al. "Formation of Hydrogen Sulfide and Glutathione During Fermentation of White Grape Musts." Am J Enol Vitic. January 2000 51: 91-97.
- ↑ Perrocheau L, Bakan B, Boivin P, Marion D. Stability of barley and malt lipid transfer protein 1 (LTP1) toward heating and reducing agents: relationships with the brewing process. J Agric Food Chem. 2006;54(8):3108−3113.
- ↑ Wu MJ, Clarke FM, Rogers PJ, et al. Identification of a protein with antioxidant activity that is important for the protection against beer ageing. Int J Mol Sci. 2011;12(9):6089–6103.
- ↑ Bamforth CW, Muller RE, Walker MD. Oxygen and oxygen radicals in malting and brewing: a review. J Am Soc Brew Chem. 1993;51(3):79–88.
- ↑ Sonni F, Clark AC, Prenzler PD, Riponi C, Scollary GR. Antioxidant action of glutathione and the ascorbic acid/glutathione pair in a model white wine. J Agric Food Chem. 2011;59(8):3940–3949.