Identification of caffeic acid as a major component of Moscatel wine protein sediment

All techniques usually used to assay proteins was not reliable in vegetable extract due to interferences with the components included in extracts like polyphenols, tanins, pectines, aromatics compounds. Absorbance at 280nm, Kjeldhal assay, Biuret and Lowry methods, Acid Bicinchonique technique and Bradford assay give the results depending on the composition of extract, on the presence or not of detergent and on the raw material (Marchal, 1995). Another difficulty in these extracts for the quantification of proteins comes from the large amount of water included in vegetable and the low concentration of proteins. Thus in red wines, proteins are usually not taken into account due to their low concentration (typically below 10 mgL-1) and to the presence of anthocyanis and polyphenols.

Vitis vinifera L. is the most widely cultivated Vitis species which includes numerous cultivars. Owing to their superior quality of grapes, these cultivars were long considered the only suitable for the production of fine wines. However, the lack of resistance genes in V. vinifera against major grapevine pathogens, requires for its cultivation frequent spraying with large amount of fungicides. Thus, the search for alternative and more sustainable methods to control the grapevine pathogens have brought the breeders to focus their attention on other Vitis species. In fact, wild Vitis genotypes present multiple resistance traits against pathogens, such as powdery mildew, downy mildew and phylloxera.

From the standpoint of wine aroma oxidation there are two effects observed: aroma degradation of oxygen sensitive compounds (polyfunctional mercaptans) and the appearance of new substances with high aromatic power (acetaldehyde, methional, phenylacetaldehyde, sotolon, alkenals, isobutanal and 2, 3-metylbutanals) (1-5). According to our experience, Strecker aldehydes are compounds with highest sensory relevance in the oxidative degradation of many wines (5-7).

C-Glucosidic ellagitannins, which are the main polyphenolic compounds in oak heartwood, are extracted by wine during aging in oak barrels. Although such maturing of alcoholic beverages in oak barrels is a multi-centennial practice, very little is known on the impact of these ellagitannins on the organoleptic properties of red wine. The objectives of the present investigation were (i) to isolate oak ellagitannins and to hemisynthesize some made-in-wine flavano-ellagitannins, such as acutissimin A; (ii) to analyse their concentration ranges depending on the cultivar area and (iii) to evaluate their sensory impact on the basis of their human threshold concentrations and dose/response relationships in different types of solutions.

Different separation techniques are frequently used during vinification process. Nowadays, clarification and microbiological stabilization of wine or beer can be done using precoat filters or crossflow filters to remove yeast and bacteria. Kieselguhr powders are the most used filter aids for precoat filtration. Their crystalline structure and their pulverulent nature induce ecotoxicological risks when used. Moreover, regeneration and reuse of these filter aids is not efficient and the filtration waste requires cost effective retreatment.