Copigmentation of Malvidin-3-O-Monoglucoside by Oenological Tannins: Incidence on Wine Model Color in Function of Botanical Origin, pH and Ethanol Content.

The effect of the botanical origin, pH level and ethanol content of different oenological tannins on the color of malvidin-3-O-monoglucoside solution, including their effectiveness as copigments, was studied. Briefly, a model wine solution (4 g/L of tartaric acid, pH 3.5 and 12% ethanol) containing 50 mg/L of malvidin-3-O-monoglucoside was prepared and supplemented with 0.1, 0.2 and 0.4 g/L of commercial tannins using (-)-epicatechin as reference control copigment. Six additional model wine solutions (12% ethanol at pH 3.1, 3.5 or 3.9, and 10%, 12% or 14% ethanol at pH 3.5) were prepared as previously described. Samples were stored under airtight conditions. After a week the full absorbance spectrum in the visible range (400-800 nm) was measured and CIELAB color space was determined. These measurements, including an increase in a* (redness), a decrease in b* (yellowness) and a decrease in L* (lightness), indicated that all oenological tannins had a clear positive effect on color copigmentation. Moreover, hydrolysable tannins appeared to be better copigments than condensed tannins as the copigmentation effectiveness (Cp) was found to be between two to four times higher. The effects of these tannins were dose-dependent because a higher addition resulted in a greater impact on copigmentation. In general, an increase in pH and ethanol content resulted in a decrease of the effect of tannins on color. Independent of intrinsic wine conditions, hydrolysable tannins, more specifically gallotannin, remain the most effective in increasing red wine color. These results prove that supplementation with oenological tannins, especially hydrolysable tannins, could be an interesting tool for the improvement of the red wine color.

Influence of grape seeds on wine composition and astringency of Tempranillo, Garnacha, Merlot and Cabernet Sauvignon wines.

BACKGROUND: The aim of this work was to study the influence of grape berry morphology, especially the seed weight percentage, on the tannin concentration and astringency of red wine. Clusters of Tempranillo, Garnacha, Merlot, and Cabernet Sauvignon were characterized and their seeds were extracted and macerated in a model wine solution. In parallel, we elaborated three types of wines of each cultivar. One wine was made with only grape juice, one wine was made adding the appropriate proportion of seeds to the grape juice, and the last wine was elaborated with the complete destemmed and crushed berries. RESULTS: Merlot and Cabernet Sauvignon grapes, which have higher percentage of seed weight with respect to the berry weight than Tempranillo and Garnacha grapes originated wines with higher tannin concentration and astringency than Tempranillo and Garnacha wines. CONCLUSION: The main conclusion of this study is that the seed weight percentage with respect to the berry weight is one of the main determinants of the final tannin concentration and astringency of red wines.

Occurrence and enological properties of two new non-conventional yeasts (Nakazawaea ishiwadae and Lodderomyces elongisporus) in wine fermentations.

The microbial diversity of wine alcoholic fermentation is not restricted to the presence and activity of Saccharomyces yeast strains. Some non-Saccharomyces species have been described as part of the fermentative microbiota, specially found in the initial steps of wine fermentations. These species may play roles from wine spoilage to flavor quality enhancement. From a large number of wine fermentations (429 wine samples), analyzed by ITS-amplicon sequencing to define their mycobiome, 2 non-conventional yeast species (Nakazawaea ishiwadae and Lodderomyces elongisporus) were detected, in a very limited number of samples but in significant levels of relative abundance. One strain of each species was isolated and their technological and enological potential have been characterized in this work. Compared with the Saccharomyces cerevisiae Viniferm Revelacion wine strain, the studied N. ishiwadae BMK17.1 and L. elongisporus BMK12.5 strains showed, as expected, a lower tolerance and growth fitness in high ethanol concentrations. However, N. ishiwadae BMK17.1 was able to grow also at 15% ethanol and L. elongisporus BMK12.5 at 10% reaching, in the latter case, slightly higher efficiency rates than S. cerevisiae at this level. Contrary to most non-Saccharomyces yeasts, these species were able to growth in presence of high doses of potassium-metabisulfite, reaching in both cases higher efficiency rates than S. cerevisiae. A notable affinity of L. elongisporus BMK12.5 for high pH values was clearly observed. Their fermentation kinetics and the final chemical-analytical characterization were studied in micro-fermentation assays, using synthetic grape must. L. elongisporus BMK12.5 was able to complete, in single inoculation, the sugar fermentation after 19 days, but, N. ishiwadae BMK17.1 left about 80 g/L sugars at this time. Co-inoculation assays (in a 1:100 proportion of S. cerevisiae:non-Saccharomyces strains) finished sugar consumption with similar kinetics than the S. cerevisiae single inoculation, in the case of L. elongisporus BMK12.5 co-inoculation, and with lower kinetics when using N. ishiwadae BMK17.1. A remarkable malic acid consumption and a low acetic acid production was associated with L. elongisporus BMK12.5 fermentations, together with a high production of 3-methyl-1-butanol and 2-phenylethanol, and the release of high amounts of proteins into the wines. N. ishiwadae BMK17.1, although unable to finish the fermentation itself, showed a high production of oligosaccharides and volatile compounds such as isobutanol or isobutyric acid. This work reports, for the first time, the occurrence and enological potential of two strains pertaining to the non-conventional yeast genera Lodderomyces and Nakazawaea.

Chemical characterization, antioxidant properties and oxygen consumption rate of 36 commercial oenological tannins in a model wine solution.

The chemical composition (CC), antioxidant capacity (AC) and oxygen consumption rate (OCR) of 36 different commercial tannins were measured. The CC was analyzed by total polyphenol index, Bate-Smith, methyl-cellulose, Folin-Ciocalteu, OIV official method and phloroglucinolisis. The AC was measured by different methods (ABTS, CUPRAC, DPPH, FRAP, ORAC) using Trolox as standard. The OCR was measured using a non-invasive method based on luminescence. The results indicate that it is possible to obtain differentiation between procyanidins/prodelphinidins, profisetinidins/prorobinetidins, gallotannins and ellagitannins by PCA based on their CC data. It is also possible to separate condensed from hydrolysable tannins by PCA based on their AC data. The results show that ellagitannins are the fastest oxygen consumers of the various oenological tannins, followed in descending order by condensed tannins and finally gallotannins. The combination of CC, AC and OCR analyses enable to classify tannins according to their effectiveness in protecting wines against oxidation.

Oxygen consumption rates by different oenological tannins in a model wine solution.

The kinetics of oxygen consumption by different oenological tannins were measured in a model wine solution using the non-invasive method based on luminiscence. The results indicate that the oxygen consumption rate follows second-order kinetics depending on tannin and oxygen concentrations. They also confirm that the oxygen consumption rate is influenced by temperature in accordance with Arrhenius law. The indications are that ellagitannins are the fastest oxygen consumers of the different oenological tannins, followed in decreasing order by quebracho tannins, skin tannins, seed tannins and finally gallotannins. This methodology can therefore be proposed as an index for determining the effectiveness of different commercial tannins in protecting wines against oxidation.

Influence of Grape Seeds and Stems on Wine Composition and Astringency.

The aim of this paper is to study the real influence of seeds and stems on wine composition, astringency, and bitterness. A decolored grape juice and a grape juice macerated for 4 days from the same Cabernet Sauvignon grapes were fermented with or without supplementation with 100% seeds, 300% seeds, or 100% stems. Once alcoholic fermentation had finished, the wines were analyzed and tasted. The presence of seeds and stems increased the concentration of flavan-3-ol monomers with respect to the controls. However, the seeds mainly released (+)-catechin and (-)-epicatechin, whereas the stems mainly released (+)-catechin and (+)-gallocatechin. The seeds and stems also released proanthocyanidins; those from seeds have a lower mDP and a high percentage of galloylation, whereas those from stems have a higher mDP and a relatively high percentage of prodelphinidins. The presence of seeds and stems brought about a slight but significant increase in pH and lowered titratable acidity and ethanol content. The presence of seeds boosted color intensity, whereas stems had the opposite effect. Finally, both seeds and stems increased wine astringency and bitterness.