Oxidative evolution of (+)-catechin in model white wine solutions containing sulfur dioxide, ascorbic acid or gallotannins

Development of a New Strategy for Studying the Oxygen Consumption Potential of Wine through the Grape Extract Evaluation

The development of a method to determine the aging potential of wine at the time of harvest, through the evaluation of its oxygen avidity, is a potential tool for the winemaking sector. To this end, it is necessary to formulate a potential wine with this grape prior to alcoholic fermentation. The main objective of this method was to optimize a formulation of the potential wine, based on the grape extracts (GEs), to subsequently evaluate its oxygen consumption kinetics, guaranteeing maximum differentiation between the different GEs. The optimization was carried out with a Taguchi orthogonal matrix design, which optimized the variables to be used in the GE reconstitution. The variables studied were pH, Fe2+, Cu2+, Mn2+, alcohol content and acetaldehyde. The evaluation of the characteristic parameters of the consumption kinetics of each of the GEs allowed us to know the different reconstitution conditions that most influence the differentiation of the oxygen consumption kinetics of very similar GEs. The reconstitution conditions chosen were pH 3.3; 1 mg/L Fe2+; 0.1 mg/L Cu2+; 1 mg/L Mn2+; 12% (v/v) alcoholic strength and 10 mg/L acetaldehyde, with pH, Fe2+ and Mn2+ being the significant conditions. The kinetics of reconstituted GE could be a tool for the classification and evaluation of grapes according to their aging potential or shelf life of the wine made.

Ozone Gas for Low Cost and Environmentally Friendly Desulfurization of Mute Grape Must

Ozone is widely used for storage and processing facilities and food sanitization. In this research, ozone was tested as an alternative to high temperature vacuum must desulfurization in order to make a more sustainable process. Bubbling ozone in highly sulfited red must (mute must) at two treatment temperatures, a significant reduction in total and free sulfites from around 1000 mg/L to 200 and 120 mg/L at 20 and 10 °C, respectively, was observed in 24 h, but already after 4 h the concentration was halved. Air flushing of the mute must did not reduce the SO₂ content. To evaluate the potential ozone effect on polyphenol oxidation, we carried out the ozone treatment on a water solution with tannins, ascorbic acid, or potassium metabisulfite (MBK) as single and as mixture. In 1 h, 2/3 of sulfite disappeared with the treatment, but the reduction was greater with ascorbate and tannins; the same was observed for ascorbate, whereas tannins decreased to a lesser extent when combined with ascorbate and MBK. Taken together, the results indicate that ozone could be an environmentally friendly, low cost, treatment for desulfurization, especially for white must, and is also easy to use by small wineries.

Characterisation of Extracts Obtained from Unripe Grapes and Evaluation of Their Potential Protective Effects against Oxidation of Wine Colour in Comparison with Different Oenological Products

Unripe grapes (UGs) are a waste product of vine cultivation rich in natural antioxidants. These antioxidants could be used in winemaking as alternatives to SO2. Three extracts were obtained by maceration from Viognier, Merlot and Sangiovese UGs. The composition and antioxidant activity of the UG extracts were studied in model solutions at different pH levels. The capacity of the UG extracts to protect wine colour was evaluated in accelerated oxidation tests and small-scale trials on both red and white wines during ageing in comparison with sulphur dioxide, ascorbic acid and commercial tannins. The Viognier and Merlot extracts were rich in phenolic acids while the Sangiovese extract was rich in flavonoids. The antioxidant activity of the extracts and commercial tannins was influenced by the pH. In the oxidation tests, the extracts and commercial products showed different wine colour protection capacities in function of the type of wine. During ageing, the white wine with the added Viognier UG extract showed the lowest level of colour oxidation. The colour of the red wine with the UG extract evolved similarly to wine with SO2 and commercial tannins. The obtained results indicated that natural and healthy UG extracts could be an interesting substitute for SO2 during wine ageing.

Air saturation methodology proposal for the analysis of wine oxygen consumption kinetics

The great heterogeneity currently present when characterizing wine consumption kinetics means that a saturation method, as well as different parameters that allow comparison between wines, need to be established. The aim of this work was to establish a robust method for a wine saturation protocol and compare different fitting models to approximate the oxygen consumption kinetics. To differentiate wines, parameters extracted from the oxygen consumption curves were studied and proposed. 72 young commercial wines (red, white and rosé) from different Spanish appellations of origin, varieties and vintages were used. The results revealed that 5 min was enough to saturate wines up to the maximum level for each one at 35 °C. The inverse curve fitting model showed the best results for all wines. Oxygen at half consumption time (O_mid) and time required to consume from 90% to 10% of the oxygen initially available (Δt_{O_90_10}) were the parameters that differentiated wines the most.

Effect of Different Reducing Agents on Aromatic Compounds, Antioxidant and Chromatic Properties of Sauvignon Blanc Wine

Sulfur dioxide (SO2) is widely the most used enological additive with reductive, antiseptic and dissolving properties. According to increasing health concerns and the gradual decrease in total SO2 concentrations allowed in wine, alternative and supplementary agents for preservation are being investigated. For this reason, the current study was focused on the impact of different commercial reductive agents on white wine antioxidant activity and chemical composition. The effect of additives that combine sulfites, ascorbic acid and enological tannins were compared against standard 5% sulfurous acid (H2SO3) during the pre-fermentative treatments of Sauvignon Blanc must (Vitis vinifera L.). The basic parameters of quality, free amino-nitrogen and total polyphenoliccompounds in must were analyzed. Gas chromatography and spectrophotometric methods were used to investigate the overall volatile composition, antioxidant and chromatic parameters in wines. The obtained results undoubtedly pointed out the positive effect of sulfuric acid on the fermentation dynamics. Furthermore, application of combined reducing additives with potassium metabisulfite, L-ascorbic acid, gallotannins and ellagitannins, resulted in a higher antioxidant capacity and increased concentration of aromatic compounds and their odor activity values in Sauvignon Blanc wine.

Efficacy of chitosan in inhibiting the oxidation of (+)-catechin in white wine model solutions

The efficacy of chitosan and sulfites in inhibiting the oxidation of (+)-catechin in aerated model white wines has been compared by monitoring the browning development and the generation of oxidized phenolic compounds. In addition, the protecting effects of these two additives toward the oxidative decay of varietal thiols were investigated. Chitosan effectively contrasted the browning onset in model solutions all along the entire duration of the experimentation. Color development was limited and comparable in both the sulfite and chitosan added samples. Thanks to its polyelectrolyte behavior, chitosan adsorbed up to 80% of the more hydrophilic oxidized phenolic species and chelated 70 and 30% of Fe and Cu added to the solutions, respectively. Thiol oxidation was significantly lowered by chitosan, suggesting that this additive could contribute to maintain the varietal character of wines coming from aromatic grapes and vinified with reduced sulfite amounts.