Browning Development and Antioxidant Compounds in White Wines after Selenium, Iron, and Peroxide Addition

The role of polyphenols in oxygen consumption and in the accumulation of acetaldehyde and Strecker aldehydes during wine oxidation

This study explores the role of polyphenols in preventing oxidative deterioration of wine aroma. Wine models containing polyphenols extracted from grapes were fortified with delphinidin-3G (DELF) or catechin (CAT), and oxidized. DELF increased oxygen consumption rates (OCRs) and reduced the Strecker aldehydes (SAs) formation, while CAT decreased OCRs and increased SAs. Further oxidation of models with individual polyphenols: coumaric acid (COU), caffeic acid (CAF), CAT, epigallocatechin (EPIG), malvidin-3G (MV), DELF, quercetin (QUER), and myricetin (MYR) revealed that most polyphenols, except anthocyanins, slowed initial OCRs. Anthocyanins and trihydroxylated polyphenols consumed all oxygen. DELF arises as the ideal sacrificial antioxidant, consuming O2 quickly and quantitatively, avoiding Fenton reaction and SAs accumulation. MV was similar but caused high SAs levels. EPIG and MYR prevented Fenton reaction but induced moderate SAs accumulation. COU hardly consumed O2, but prevented Fenton reaction and did not induce SAs. These findings could help enhance wine quality and stability.

Copper (II) Level in Musts Affects Acetaldehyde Concentration, Phenolic Composition, and Chromatic Characteristics of Red and White Wines

Copper (II), a vital fungicide in organic viticulture, also acts as a wine oxidation catalyst. However, limited data are currently available on the impact that maximum allowed copper (II) ion doses in wine grapes at harvest can have on aged wine quality. This was the focus of the present study. We investigated the copper (II) effects by producing both white and red wines from musts containing three initial metal concentrations according to the limits set for organic farming. In detail, the influence of copper (II) on fermentation evolution, chromatic characteristics, and phenolic compounds was evaluated. Interestingly, the white wine obtained with the highest permitted copper (II) dose initially exceeded the concentration of 1.0 mg/L at fermentation completion. However, after one year of storage, the copper (II) content fell below 0.2 ± 0.01 mg/L. Conversely, red wines showed copper (II) levels below 1.0 mg/L at the end of fermentation, but the initial copper (II) level in musts significantly affected total native anthocyanins, color intensity, hue, and acetaldehyde concentration. After 12-month aging, significant differences were observed in polymeric pigments, thus suggesting a potential long-term effect of copper (II) on red wine color stability.

Non-enzymatic browning of wine induced by monomeric flavan-3-ols: A review

Non-enzymatic browning occurs widely in both white and red wines, and it has a huge impact on the color evolution and aging potential. Previous studies have proved that phenolic compounds, especially those with catechol groups, are the most important substrates involved in browning reactions of wine. This review focus on the current knowledge of non-enzymatic browning in wine resulting from monomeric flavan-3-ols. First, some relevant aspects of monomeric flavan-3-ols are introduced, including their structures, origins, chemical reactivities, as well as potential impacts on the organoleptic properties of wine. Second, the mechanism for non-enzymatic browning induced by monomeric flavan-3-ols is discussed, with an emphasis on the formation of yellow xanthylium derivatives, followed by their spectral properties and effects on the color change of wine. Finally, attentions are also be given to the factors that influence non-enzymatic browning, such as metal ions, light exposure, additives in winemaking, etc.

Wine Faults: State of Knowledge in Reductive Aromas, Oxidation and Atypical Aging, Prevention, and Correction Methods

The review summarizes the latest scientific findings and recommendations for the prevention of three very common wine faults of non-microbial origin. The first group, presented by the reductive aromas, is caused mainly by excessive H₂S and other volatile sulfur compounds with a negative impact on wine quality. The most efficient prevention of undesirable reductive aromas in wine lies in creating optimal conditions for yeast and controlling the chemistry of sulfur compounds, and the pros and cons of correction methods are discussed. The second is browning which is associated especially with the enzymatic and non-enzymatic reaction of polyphenols and the prevention of this fault is connected with decreasing the polyphenol content in must, lowering oxygen access during handling, the use of antioxidants, and correction stands for the use of fining agents. The third fault, atypical aging, mostly occurs in the agrotechnics of the entire green land cover in the vineyard and the associated stress from lack of nutrients and moisture. Typical fox tones, naphthalene, or wet towel off-odors, especially in white wines are possible to prevent by proper moisture and grassland cover and alternating greenery combined with harmonious nutrition, while the correction is possible only partially with an application of fresh yeast. With the current knowledge, the mistakes in wines of non-microbial origin can be reliably prevented. Prevention is essential because corrective solutions for the faults are difficult and never perfect.