Efficacy of tannins of different botanical origin as partial or total substitute of SO₂ to preserve a Cortese white wine during storage in cellar

Abstract

While SO₂ is one of the oldest and widest additive used in enology for its well-known antioxidant, anti-laccase and antimicrobial properties, it can cause health problems in some individuals. Nowadays, the antioxidant and antiradical qualities of alternative oenological practices or additives are currently being investigated, and several papers have been published that thoroughly examine the mechanisms governing the oxidation reactions to establish the theoretical basis for lowering the use of SO₂ in wines. Currently, the risk of a shorter shelf life is increased by the complete lack of sulfur dioxide, particularly for white wines. Although oenological tannins are one of the most suitable substitute products for antioxidant activity, the majority of researches have been done using model wine solutions or wines with sulfites. In this study a Cortese white wine vinified in the absence of SO₂, was divided in two parts: one with 30 mg/L of free sulfur dioxide (+SO₂) and one without (-SO₂). Each group was further divided into four samples and treated with different tannins (25 mg/L): ellagic tannin (American oak, A), condensed tannin (green tea, T and mimosa, M), gallotannin (chinese gall, G). The aim of the work was to study the efficacy of different tannins as partial or total substitute of SO₂ to preserve white wines during storage in cellar. Parameters related to oxidation were measured during storage: changes in color (CIELab) and polyphenols (total polyphenols and flavans), acetaldehyde, free and total SO₂, oxygen consumption rate (OCR), redox properties (linear sweep voltammetry – LSV), sensory profile. At the beginning of storage, the + SO₂ had a significantly lower OCR compared to the – SO₂. This is because the Fenton reaction, a rapid oxidation reaction, is favored in the absence of sulfites. The addition of tannins reduced the OCR, with the extent of reduction varying depending on the type of tannin. These findings, which contradict previous research on tannins in model solutions, may be attributed to the tannins’ chelating and anti-radical properties. LSV revealed that SO₂ had a protective effect at the beginning of storage (increase in oxidizable compounds). However, this effect diminished after six months as the SO₂ levels decreased. conversely, tannins appeared to exhibit a protective effect only after six months, particularly T. Throughout storage, a significant increase in acetaldehyde was observed in all the +SO2 wines, especially when free SO₂ levels dropped below 10 mg/L. Wines treated with hydrolysable tannins had higher acetaldehyde content. Sensory analysis indicated significantly higher oxidized notes in the samples treated with ellagic tannin (E), both in the + SO₂ and – SO₂ groups. These samples also exhibited the highest levels of acetaldehyde. LSV results confirmed these sensory findings, suggesting that LSV could be a quick, user-friendly, and suitable technique for evaluating the oxidative evolution of wines over time.