Degradation of tannic acid by cell-free extracts of Lactobacillus plantarum

Resumen del póster presentado al 2nd Annual Meeting COST 928, celebrado en Istanbul (Turquía) del 15 al 17 de octubre de 2008.
In foods, tannins are considered nutritionally undesirable. However, the intake of a small quantity of the right kind oftannins may be beneficial to human health. It has been found that the higher the molar mass of tannin molecules, the stronger the antinutritional effects and the lower the biological activities. Microbial degradation is one of the efficient ways to degrade large molecular tannins into smaller molecular tannins with valuable bioactivities. In this work we evaluated the ability of Lactobacillus plantarum to degrade hydrolysable tannins. Significative reduction of tannic acid was not observed during incubation in the presence of L. plantarum cells after 7 days incubation. However, tannic acid was effectively degraded by cell-free extracts containing soluble proteins from L. plantarum. By HPLC analysis, almost a complete tannic acid degradation was observed in the three commercial tannic acid samples assayed. By using HPLC-DADIESI-MS, we partially determined the composition of tannic acid from Quercus infectoria galls. This tannic acid is a gallotannin mainly composed of monomers to tetramers of gallic acid. We studied the mechanism of its degradation by L. plantarum. The results indicated that L. plantarum degrades gallotannins by depolymerization of high molecular weight tannins and a reduction of low molecular weight tannins. Gallic acid and pyrogallol were detected as final metabolic intermediates.