Effects Of Two Common Antioxidants On Acetaldehyde Accumulation In Wine

During the ageing process,the winemaker usually enriches the flavour profile of the wine through suitable exposure to oxygen,allowing the wine to develop towards the colour,taste and aroma expected by the consumer,in order to promote a mature and stable wine,all these changes are inseparable from oxidation reactions.Acetaldehyde,the main product of wine oxidation,is one of the most abundant colourless volatile aldehydes in wine and can influence the colour and flavour characteristics of wine,playing an important role in wine quality and is a key compound that cannot be ignored,so monitoring the accumulation of acetaldehyde can effectively track the oxidation process of wine.During this process,a certain amount of antioxidant is usually added to prevent the adverse effects of oxidation.The traditional antioxidant used in winemaking is sulphur dioxide（SO₂）,which is still widely used,and in recent years reduced glutathione（GSH）is also starting to be experimented with.In this work,the effect of SO₂ and GSH on the accumulation of acetaldehyde during wine oxidation was investigated using mock wines and Cabernet Sauvignon dry red wines,and the possible reaction mechanisms of wine oxidation under changes in acetaldehyde content were elucidated through the measurement of a series of oxidation indicators.The main results obtained were as follows:（1）The model wines were treated with aeration to achieve a dissolved oxygen level of around 10 mg/L,followed by the addition of 0（Control）,30（MLS）,60（MMS）and120（MHS）mg/L of SO₂.Dissolved oxygen,Fe²⁺concentration,hydroxyl radical fluorescence intensity and acetaldehyde were monitored at different stages of subsequent ageing.The results showed that there was no significant accumulation of acetaldehyde in both the MLS and Control groups when free state SO₂ was present,but the accumulation of acetaldehyde in the MLS group was significantly lower than that in the Control group when free state SO₂ was depleted in both the MLS and MMS groups,but the accumulation of acetaldehyde in both the MMS and MHS groups was significantly higher than that in the Control group,1.02 mg/L and 2.96 mg/L more than that in the Control group,respectively.The changes in fluorescence intensity of hydroxyl radicals were consistent with the accumulation of acetaldehyde.Therefore,low concentration of SO₂ could significantly inhibit the formation of acetaldehyde,but the accumulation of acetaldehyde became more pronounced as the concentration of SO₂increased,indicating that high concentration of SO₂ has a catalytic oxidation effect.The addition of SO₂ formed sulphite radicals in the wine solution,and the continued addition of oxygen resulted in the formation of a highly oxidised peroxymonosulfate radical(SO₅^·-),which was able to oxidise sulphite to regenerate the sulphite radical and continue the chain reaction with the radical,with the addition of sulphur group consuming more Fe³⁺,thus promoting the oxidation of Fe²⁺and thus advancing the oxidation process and the formation of acetaldehyde accumulation.（2）The model wine was treated with aeration to achieve a dissolved oxygen level of around 12 mg/L.0（Control）,20（MLG）,40（MMG）and 80（MHG）mg/L GSH were added,and the same analytical studies as the SO₂ addition experiment were carried out at different stages of subsequent ageing,showing that the addition of GSH to the mock wine after the aeration treatment caused a The results showed that the addition of GSH caused a significant accumulation of acetaldehyde in the mock wine after the aeration treatment,with the acetaldehyde content in the GSH-added group being significantly higher than in the Control group.When only the MHG group had a small amount of GSH present,the accumulation of acetaldehyde increased significantly with the increase in GSH concentration,with the MLG,MMG and MHG groups being 0.8 mg/L,1.9mg/L and 2.7 mg/L higher than the Control group,respectively,and the change in fluorescence intensity of hydroxyl radicals was opposite to the change in the accumulation of acetaldehyde,thus it could be found that the pathway of GSH leading to the accumulation of acetaldehyde was different from that of GSH is not the same as SO₂,as it accelerates the consumption through the rapid reaction with quinones and may act as a"nucleophile to promote oxidation",which leads to the conversion of Fe²⁺to Fe³⁺and accelerates the formation of hydroxyl radicals,resulting in the accumulation of acetaldehyde.（3）The model wine was treated with aeration to achieve a dissolved oxygen level of around 8 mg/L,30 mg/L SO₂ and 20 mg/L GSH（MLSLG）,30 mg/L SO₂ and 80mg/L GSH（MLSHG）,120 mg/L SO₂ and 20 mg/L GSH（MHSLG）,120 mg/L SO₂ and80 mg/L GSH（MHSHG）and no added antioxidants（Control）,and the changes in acetaldehyde accumulation at different combinations of the two antioxidants were tracked at different stages of subsequent ageing.The results showed that only acetaldehyde in the WLSLG was not significantly different from the Control group at these four combinations of antioxidant concentrations,while acetaldehyde accumulation was not suppressed in any of the other simulated wines.In the presence of free state SO₂,acetaldehyde accumulation was significantly higher in both MHSLG and MHSHG than in MLSLG,MLSHG and Control,and not significantly different between MLSLG and MLSHG but significantly higher than in the Control group,where they were 1.9 mg/L,1.5 mg/L and 0.3 mg/L higher,respectively,than in the Control group.L.After depletion of free state SO₂ in the two low sulphur groups,their acetaldehyde accumulation was not significantly different from that of the Control,and the MHSLG and MHSHG groups were significantly higher than the low sulphur and Control groups,by 3.3 mg/L and 2.2 mg/L,respectively,indicating that SO₂ was predominant in the accumulation of acetaldehyde under the combination of these four concentrations of antioxidants.After the free state SO₂ was depleted,GSH promoted the accumulation of acetaldehyde by other means.（4）Select Cabernet Sauvignon red wines,just finished alcoholic fermentation,were treated with 30 mg/L SO₂（WLS）,120 mg/L SO₂（WHS）,30 mg/L SO₂ and 20mg/L GSH（WLSLG）,30 mg/L SO₂ and 80 mg/L GSH（WLSHG）,120 mg/L SO₂ and20 mg/L GSH（WHSLG）,120 mg/L SO₂ and 80 mg/L GSH（WHSHG）,four aeration treatments with a total of approximately 21.2 mg/L of oxygen,and then after the free SO₂ was depleted,an antioxidant was added at the corresponding concentration to investigate the causes of the changes in acetaldehyde content in the wines according to the trends in oxidation parameters.The effect of WLSLG on the colour change was also investigated by CIELab model analysis.The experimental results showed that the two antioxidants in the WLSLG group acted synergistically to inhibit oxidation and therefore did not cause the accumulation of acetaldehyde,which was only 6.8 mg/L at this time.In both the WLS group,the continued addition of 20 mg/L GSH（WHS-LG）and WLSHG after depletion of free state SO₂ eventually promoted the accumulation of acetaldehyde,with acetaldehyde accumulating at 24.4 mg/L,24.9 mg/L and 26.4 mg/L,respectively.In the WHS group,it was also the hysteresis effect of SO₂ that played a key role,resulting in the accumulation of acetaldehyde at 24.1 mg/L.WHS-LG and WHS-HG,which played a somewhat synergistic role,inhibited the onset of oxidation.