Characterization of proteic content of gelatins

Enological gelatins are currently used in the red wines collage. We found those gelatins added with particular composants in white wines treatment. 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. 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.

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