Impact of addition of fumaric acid and glutathion at the end of alcoholic fermentation on Cabernet-Sauvignon wine

Abstract

Viticulture and oenology face two major challenges today, climate change and the reduction in the use of inputs. Climate change induces low acidity and microbiologically less stable wines (1), implying more important sulfur dioxide doses to protect wines. This is incompatible with the reduction of inputs. Fumaric acid (FA) is known for its high acidifying power and its bacteriostatic properties (2) and glutathione (GSH) for its antioxidant power (3). FA combined with GSH could solve acidity problems and reduction of sulfur dioxide in wine. The study aims to evaluate the impact of FA and/or GSH addition at the end of alcoholic fermentation (AF) and just before bottling on wine quality compared to sulfite free, sulfited wine control and tartaric acid (TA) acidified wine. This work only presents the impact of addition of FA and GSH at the end of AF on Cabernet Sauvignon wine. Micro-winemakings were conducted with high mature Cabernet Sauvignon grapes. 9kg of grapes were vatted in each tank with 60mg/L sulfur dioxide. Duplicated vats were treated with TA (2.5g/L), FA (2.5g/L tartaric acid eq.), with 50mg/L GSH, with FA (2.5g/L tartaric acid eq.) + GSH (50mg/L) and three tanks were untreated (controls). At bottling, control wines were mixed and half part was added with sulfur dioxide (80mg/L). Oenological parameters, color, phenolic compounds, antioxidant capacities were evaluated at the end of AF, the end of malolactic fermentation (MLF) and 3 months after bottling. A ranking test and sensory profiles were realized on three-months wines. TA and FA addition at end of AF induced a similar decrease of pH. Total acidity was slightly higher in tanks where FA was added. In these same tanks, the MLFs were stopped when they had already started or did not start: MLFs were delayed for 2-3 months. Wines treated with FA produced 100% more lactic acid than control and TA-acidified wines. Color differences were observed in three-months wines after AF addition. The sulfited control was the lightest with more yellow hue and the wines with added FA were the darkest ones. Total phenolic compounds (total phenolic index and Folin-Ciocalteu analysis) were slightly lower in wines treated with FA and/or GSH. Total tannins were not affected by treatments unlike total anthocyanins. Their content in wine treated with FA without GSH was the lowest. In contrast, addition of GSH had a protective effect on total free anthocyanins. Antioxidant capacities were similar in all wines. Concerning organoleptic quality of wines, the ranking test on overall quality did not show differences but FA acidified wine was the best ranked. Sensory profils highlighted that sulfited control was less intense with more yellow hue. Acidified wines, especially with TA, and GSH added wine were slightly more aromatic than control wines. Addition of FA at the end of AF (2.5g/L tartaric acid eq.) allowed to delay MLF and produced 100% more lactic acid than control wines.