Evaluation of a oxygenate based plant protection treatment in viticulture against fungal diseases

Over the last decades the use of pesticides in vine protection, e.g. copper is under severe discussion and is becoming a major concern in viticulture. Since the effectiveness of oxygenates against various microorganisms had been proven in the medical field a strategy for oxygenate-based plant protection was developed and evaluated over three vintages. The production of the oxygenate is following the Criegee-mechanism using O3 and unsaturated natural plant derived fatty acids forming so called ozonides. Therefore the effect of the treatment has been evaluated in a holistic approach, covering the efficiency against fungal diseases, protection of desired beneficial insects, the micro flora, various secondary metabolites of the grapevine and the resulting sensory profile of the wines. The biological effectiveness has been measured by using different in-vivo and in-vitro studies. The influence on desired berry compounds, e.g. anthocyanins, have been determined by classical GC-MS and HPLC methods. Positive effects against downy and powdery mildew could be demonstrated. No negative effects against insects, naturally occurring microorganisms, and desired berry compounds were observed. Even spontaneous fermentation was not inhibited. Quantitative descriptive sensory analysis as well as CATA/RATA showed no negative effect of the treatment

Verification of the practical suitability of cation exchangers for lowering the pH value in must and wine

Due to climate change, grapes are reaching continuously higher levels of technological maturity. However, this also leads to lower acidity levels and higher pH values in musts and wines. Higher pH values would result in higher risk potential regarding undesirable microorganisms, associated with wine faults. Since 2013, cation exchangers have been allowed for acidification. In addition, yeasts of the genus Lachancea releasing lactic acid during fermentation to lower the pH of the wine. In addition to lowering the pH value, cation exchangers have the advantage of increasing tartaric stability, so that other methods can be avoided. Musts were treated in repeated trials. For comparison, the process was also used in wine. In addition, the lactic acid-producing yeast Lachancea thermotolerans was used. The use of a cation exchanger in must or wine always led to a complete removal of potassium and calcium, and at the same time the pH value dropped in some cases to 2.11. Therefore, only part (20%) of a must or wine may be treated to make the final adjustment. The use of the yeast Lachancea thermotolerans could lead to an increase of up to 6 g/L lactic acid, which resulted in an increase of the total acidity

Influence of Lysozyme Addition on Hydroxycinnamic Acids and Volatile Phenols during Wine Fermentation

Most yeast and bacteria in wine are able to metabolize hydroxycinnamic acids into volatile phenols via enzyme-mediated decarboxylation. Our trials performed in wine and model systems suggest that lysozyme addition prior to fermentation affects both bacterial activity and the release of hydroxycinnamic acids from their tartrate esters. This increases the potential for volatile phenol formation, as microorganisms can only metabolize free hydroxycinnamates. Wines with delayed malolactic fermentation due to lysozyme addition contained significantly higher concentrations of free hydroxycinnamic acids and elevated levels of volatile phenols in some cases. The reason for this is likely related to the side activity of lysozyme in combination with a detoxification mechanism that only occurs under stressful conditions for the yeast. Experiments in model systems indicate that lysozyme can affect the yeast at a pH higher than usually found in wine by attacking chitin in the bud scars of the cell walls and therefore weakening the cell structure. Free hydroxycinnamates can also affect yeast viability, making an increased release during fermentation problematic for a successful fermentation

Use of glutathione during white wine production – impact on S-off-flavors and sensory production

Recently two OIV resolutions (OENO 445-2015 and OENO 446-2015) were adopted, defining the use of glutathione (GSH) up to a maximum level of 20 mg/L in must and wine. Various studies have shown the benefits of GSH addition, especially in Sauvignon blanc wines. On the other hand, the formation of hydrogen sulfide (H2S) and other S-off-flavors favored by GSH addition are reported. To investigate the effect of glutathione on the color development, the sensory expression and the formation of sulfide off-flavors, Riesling, Sauvignon Blanc and Chardonnay grapes were processed under different conditions and musts were obtained with different phenolic contents. By the addition of GSH as a pure substance or the use of GSH-rich inactivated yeast preparations, the GSH concentration in the musts was varied. Bottled wines showed generally lower GSH levels than the corresponding musts. However, higher GSH concentrations after yeast aging could be determined, which may explain increased protection against oxidation during further storage. The sensory analysis after bottling showed that the fruity character of Riesling and Sauvignon blancs was enhanced at moderate GSH addition. Overuse of GSH in musts with low phenolic content, however, can lead to sensory perceptible S-off-flavors in the later wines

Use of glutathione during white wine production – impact on S-off-flavors and sensory production

Recently two OIV resolutions (OENO 445-2015 and OENO 446-2015) were adopted, defining the use of glutathione (GSH) up to a maximum level of 20 mg/L in must and wine. Various studies have shown the benefits of GSH addition, especially in Sauvignon blanc wines. On the other hand, the formation of hydrogen sulfide (H2S) and other S-off-flavors favored by GSH addition are reported. To investigate the effect of glutathione on the color development, the sensory expression and the formation of sulfide off-flavors, Riesling, Sauvignon Blanc and Chardonnay grapes were processed under different conditions and musts were obtained with different phenolic contents. By the addition of GSH as a pure substance or the use of GSH-rich inactivated yeast preparations, the GSH concentration in the musts was varied. Bottled wines showed generally lower GSH levels than the corresponding musts. However, higher GSH concentrations after yeast aging could be determined, which may explain increased protection against oxidation during further storage. The sensory analysis after bottling showed that the fruity character of Riesling and Sauvignon blancs was enhanced at moderate GSH addition. Overuse of GSH in musts with low phenolic content, however, can lead to sensory perceptible S-off-flavors in the later wines

Influence of ascorbic acid, sulfur dioxide and glutathione on oxidation product formation in wine-like systems

The impact of the addition of ascorbic acid, sulfur dioxide and glutathione on oxidation product formation under accelerated oxidative conditions was evaluated in model wines. The effects of these antioxidants have been compared in aqueous ethanol solutions containing (+)-catechin and metal ions at pH 3.2 by monitoring O2 consumption, color evolution by CIELab, as well as (+)-catechin and glutathione decrease by LC-DAD/FD. The analysis of oxidation products formation was focused on the determination of yellowish colored xanthylium compounds by LC-ESI-ToFMS and acetaldehyde by HS-GC-FID. The results could show, that under some conditions glutathione could not inhibit carboxymethine-briged (+)-catechine dimer formation and subsequent xanthylium cation pigment generation, compared to ascorbic acid or sulfur dioxide addition providing a good protec- tion against oxidative color changes. In systems containing 0.08–0.32 mmol/L glutathion without any further addition of SO2 or ascorbic acid, increasing acetaldehyde concentrations could be observed. These results demonstrate clearly the need for further research to highlight the reactions of glutathione

Impact of climate change on grape cluster structure, grape constituents, and processability

Over the last 20 years in the Pfalz region of Germany, GDD were highest in the vintages 2018-2020. To visualize the effect of climate change for the Pfalz region of Germany, the development of TSS and TAwere documented during Pinot noir grape ripening for the vintages 1998-2021. It was observed that climate change causes sooner and accelerated ripening, however, sooner or accelerated ripening were not connected with each other. The presented study investigated the impact of vintages on berry physiology development, ripening heterogeneity in grape clusters, changes in grape constituent concentrations and their extractability with progressing grape maturity. Pinot noir and Cabernet Sauvignon, both cultivated in the Pfalz region, were compared during three consecutive vintages. Different maturities were considered in the range of 17-25 Brix and berry size distribution was documented. The changes in grape constituent concentrations and their extractability with progressing grape maturity were analyzed using HPLC-DAD/FD, LC-QToF-MS and protein precipitation assay. It was revealed that tannin extractability differs for grape varieties and vintages and progressing maturity seemed to have only a small influence on the extractability of anthocyanins

Influence of ascorbic acid, sulfur dioxide and glutathione on oxidation product formation in wine-like systems

The impact of the addition of ascorbic acid, sulfur dioxide and glutathione on oxidation product formation under accelerated oxidative conditions was evaluated in model wines. The effects of these antioxidants have been compared in aqueous ethanol solutions containing (+)-catechin and metal ions at pH 3.2 by monitoring O2 consumption, color evolution by CIELab, as well as (+)-catechin and glutathione decrease by LC-DAD/FD. The analysis of oxidation products formation was focused on the determination of yellowish colored xanthylium compounds by LC-ESI-ToFMS and acetaldehyde by HS-GC-FID. The results could show, that under some conditions glutathione could not inhibit carboxymethine-briged (+)-catechine dimer formation and subsequent xanthylium cation pigment generation, compared to ascorbic acid or sulfur dioxide addition providing a good protec- tion against oxidative color changes. In systems containing 0.08–0.32 mmol/L glutathion without any further addition of SO2 or ascorbic acid, increasing acetaldehyde concentrations could be observed. These results demonstrate clearly the need for further research to highlight the reactions of glutathione