Influence of Molecular Size of Gelatin on Reaction with Tannic Acid

Abstract

Tannin-protein complexes are known to be important in the fining of wines. This study was carried out to investigate the influence of the molecular size of gelatin on the reaction with tannic acid.

Calfskin gelatin was chromatographed on a Sephadex G-75 column in order to yield a homogenous high molecular weight fraction. The main fraction contained 95% of the original protein material. Tannic acid was purified on a Silica-gel column to separate the low molecular weight components. Gallic acid, and an unidentified compound, which gave no precipitation with gelatin, were separated. The yield on the high molecular weight fraction was 70% of the starting material.

Acid hydrolysis was used to produce fractions of gelatin of different molecular sizes. The hydrolyzed protein material was chromatographed on a Sephadex G-75 column and the separate fractions of varying molecular weights were compared with respect to their reaction with the purified tannic acid. The result showed that the amount of the precipitate decreased with decreasing molecular weight of the gelatin. This decrease in the amounts of tannic acid and protein in the precipitate as the protein fractions decreased in molecular weight is most readily accounted for by a greater solubility of the tannic acid-protein complexes formed with such protein fractions of lower molecular weight.