How acetaldehyde reacts with low molecular weight phenolics in white and red wines

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.

Enhanced Expression of Alcohol Dehydrogenase I in Pichia pastoris Reduces the Content of Acetaldehyde in Wines

Acetaldehyde is an important carbonyl compound commonly detected in wines. A high concentration of acetaldehyde can affect the flavor of wines and result in adverse effects on human health. Alcohol dehydrogenase I (ADH1) in Saccharomyces cerevisiae catalyzes the reduction reaction of acetaldehyde into ethanol in the presence of cofactors, showing the potential to reduce the content of acetaldehyde in wines. In this study, ADH1 was successfully expressed in Pichia pastoris GS115 based on codon optimization. Then, the expression level of ADH1 was enhanced by replacing its promoter with optimized promoters and increasing the copy number of the expression cassette, with ADH1 being purified using nickel column affinity chromatography. The enzymatic activity of purified ADH1 reached 605.44 ± 44.30 U/mg. The results of the effect of ADH1 on the content of acetaldehyde in wine revealed that the acetaldehyde content of wine samples was reduced from 168.05 ± 0.55 to 113.17 ± 6.08 mg/L with the addition of 5 mM NADH and the catalysis of ADH1, and from 135.53 ± 4.08 to 52.89 ± 2.20 mg/L through cofactor regeneration. Our study provides a novel approach to reducing the content of acetaldehyde in wines through enzymatic catalysis.

Effectiveness of E-Beam Radiation against Saccharomyces cerevisiae, Brettanomyces bruxellensis, and Wild Yeast and Their Influence on Wine Quality

The simplest way to eliminate microorganisms in the must/wine is through sulfuration, as it allows the introduction of pure yeast varieties into the must, which guarantees a high-quality wine. However, sulfur is an allergen, and an increasing number of people are developing allergies to it. Therefore, alternative methods for microbiological stabilization of must and wine are being sought. Consequently, the aim of the experiment was to evaluate the effectiveness of ionizing radiation in eliminating microorganisms in must. The sensitivity of wine yeasts, Saccharomyces cerevisiae, S. cerevisiae var. bayanus, Brettanomyces bruxellensis, and wild yeasts to ionizing radiation was com-pared. The effects of these yeasts on wine chemistry and quality were also determined. Ionizing radiation eliminates yeast in wine. A dose of 2.5 kGy reduced the amount of yeast by more than 90% without reducing the quality of the wine. However, higher doses of radiation worsened the organoleptic properties of the wine. The breed of yeast used has a very strong influence on the quality of the wine. It is justifiable to use commercial yeast breeds to obtain standard-quality wine. The use of special strains, e.g., B. bruxellensis, is also justified when aiming to obtain a unique product during vinification. This wine was reminiscent of wine produced with wild yeast.. The wine fermented with wild yeast had a very poor chemical composition, which negatively affected its taste and aroma. The high content of 2-methylbutanol and 3-methylbutanol caused the wine to have a nail polish remover smell.

Experimental and theoretical studies on the acetaldehyde reaction with (+)-catechin

Acetaldehyde plays a key role in determining some wine properties. Interesting is the reaction of acetaldehyde with flavonoids, as the ensuing products can alter wine color, astringency, colloidal stability. Many studies reported on the formation of ethylidene-bridged flavan-3-ols as products of the reaction between acetaldehyde and either (+)-catechin or (-)-epicatechin. In white wines after one year of incubation with acetaldehyde only vinyl-(+)-catechin and vinyl-(-)-epicatechin were observed, while no ethylidene linked oligomers were detected. This observation prompted us to study the reaction of (+)-catechin with acetaldehyde in wine model solution through an experimental and theoretical approach, with the purpose of exploring the nature of the species involved along with the mechanisms leading to them. The products of the reaction were observed over 38 days. The results showed that ethylidene-bridged catechins are the first products to be formed but over time the dissociation of these dimers causes vinyl-catechins to accumulate.

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

The effect of oxidation on the organoleptic properties of white wines mostly involves increased browning color, loss of the fruity aromas, and appearance of unpleasant odors. Browning, however, is known to be related with polyphenol oxidation and therefore it may be delayed by the presence of antioxidants such as selenium (Se) and SO2. On the other hand, the presence of oxidants such as metal ions and H2O2 can accelerate browning and oxidation phenomena. The browning capacity, the phenolic composition (both total and individual contents of flavanols and hydroxycinnamic acids), the antioxidant activity, and the SO2 content of Assyrtiko white wines were studied after the addition of Fe2+ and H2O2 and Se at two temperatures, employing an accelerated test. Browning was approached from a kinetic point of view, and the study was focused on the implication of oxidants and antioxidants on browning rate, paying particular attention to the content of major redox-active polyphenols, including substances with an o-diphenol feature, such as flavanols and hydroxycinnamic acids. The results showed that after the addition of oxidants it was possible to significantly accelerate the rate of browning development (up to 4.7 and six times) depending on the temperature and the concentration of the added compounds. The presence of Se protected wine color and preserved total SO2 at 35 °C, while at 50 °C, these effects were not observed. Total flavanol content decreased upon heating, while total hydroxycinnamic content showed a slight increase. Similarly, the content of the individual phenolic compounds (with the exception of caffeic acid and (+)-catechin at 35 °C) was decreased with oxidant addition, while Se addition was not adequate to prevent or even promote their oxidation.