Effect of SO2, glutathione, and glutathione-rich inactive dry yeast on the color, phenolic compounds, ascorbic acid, and antioxidant activity of Roxburgh rose wine

Abstract

Conventional methods for inhibiting browning in wine are not suitable for cili (Roxburgh rose) wine, which is naturally rich in ascorbic acid and subject to restrictions on SO₂ addition. In this study, the capacity of various additives to suppress the browning of cili wine caused by ascorbic acid degradation was investigated. SO₂, pure reduced glutathione (GSH), regular inactive dry yeast (IDY), and IDY with various levels of glutathione enrichment (g-IDY) were separately introduced into cili wine following the completion of alcoholic fermentation. Over a period of 12 months, the color parameters, levels of ascorbic acid, phenolic compounds, antioxidant activity, and GSH content of the aged cili wine were analyzed. Among the investigated additives, g-IDY exhibited the strongest inhibitory effect on browning. Moreover, adding 800 mg L^-1 g-IDY increased the total reducing power and residual GSH content by factors of 1.52 and 2.44, respectively, with respect to those of the SO₂-treated cili wine, thus enhancing its antioxidant capacity. Using ultra-performance liquid chromatography-tandem mass spectrometry analysis, a total of 22 monomeric phenolic compounds were identified. After g-IDY treatment, the contents of 15 easily oxidizable o-diphenols decreased, preventing the depletion of ascorbic acid as an antioxidant. As a result, the levels of ascorbic acid and total phenolics were 1.5-fold and 1.17-fold higher than those in the SO₂-treated wine, respectively. This study demonstrates that g-IDY provides a new approach to preventing the browning of wine caused by ascorbic acid degradation. PRACTICAL APPLICATION: Cili wine, characterized by its high ascorbic acid content, can decelerate cellular senescence and bolster immune function, which has contributed to its popularity. Ascorbic acid, a potent antioxidant, can be spiked into white wines to significantly enhance their antioxidative properties. Nevertheless, the high ascorbic acid content in cili wine renders it susceptible to oxidation under both aerobic and anaerobic conditions, which alters the wine's hue from golden to dark brown, thus diminishing its commercial value. Overcoming this browning associated with ascorbic acid degradation is therefore of considerable importance and could facilitate the advancement of the cili industry.

Keywords: browning; dry yeast; glutathione‐enriched inactive.