<p style="text-align: justify;">Les auteurs proposent une nouvelle technique d'estimation du degré de polymérisation des tanins du raisin et du vin, utilisant un aldéhyde spécifique des structures phénoliques renfermant des noyaux phloroglucinols ; la ρ-dimethylaminocinnamaldéhyde (DMACH). Cet aldéhyde est utilisé pour la première fois pour la détermination du degré de condensation des procyanidines. L'indice obtenu avec cet aldéhyde est d'autant plus faible que le degré de polymérisation des tanins est élevé. Le protocole retenu permet de réaliser des mesures avec un coefficient de répétabilité moyen de 5 p. cent (au seuil de confiance α = 95 p. cent). La méthode permet, d'une part d'estimer le degré de polymérisation moyen des procyanidines et d'autre part de mesurer l'influence de certaines pratiques (consommation de l'oxygène dissous, ajout d'acetaldéhyde, supplémentation en extrait phénolique) sur la variation du degré de condensation moyen des tanins.</p>
<p style="text-align: justify;">Enological gelatins are currently used in the red wines collage. We found those gelatins added with particular composants in white wines treatment.</p><p style="text-align: justify;">The Kjeldahl method recommanded by the Enology Codex gives the global concentration in nitrogen containing compounds. In order to characterize the protein content of oenological gelatins, simple and rapid determinations, based on colorimetric reactions have been selected. The proteic concentrations have been determined from commercial kits SIGMA : Biuret and Ninhydrin reactions are both concerned. They have a good repetability (variation coefficient < 6 p. cent). With Biuret, hot soluble gelatins have high concentrations, instead cold soluble and liquid gelatins have light concentrations. With Ninhydrin, results are reversed. A coefficient corresponding to the ratio of those two methods allows to characterize the hydrolyse degree of proteic chains : C = [B] / [N], Gelatins can be classified in two groups : C < 35 for cold soluble and liquid gelatins , C > 35 for hot soluble gelatins.</p><p style="text-align: justify;">Otherwise, results obtained in Kjeldahl and Biuret methods are proportional. In fact, the authors suggest a limit proteic concentration expressed in mg BSA/g solid gelatin : 750 mg BSA /g corresponding to the standard decided by the Codex, 14 % nitrogen minimum.</p>
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