Effect of vescalagin and gallic acid from chestnut tannins on microbial community profile: preliminary results

The aim of the present study was to evaluate how the rumen community, the fatty (FA) and dimethylacetal (DMA) profile can be affected by vescalagin and gallic acid, the major components in chestnut tannins. Ewe rumen liquor (LR) was buffered with McDougall saliva and inoculated with four feeds (basal diet as negative control – diet C – formulated with tannin-free ingredients; basal diet supplemented with chestnut tannin extract as positive control – diet CHT – at the inclusion level of 1.6 g/100 g of dry matter (DM); basal diet supplemented with vescalagin – diet VES – at the inclusion level of 0.24 g/100 g of DM; basal diet supplemented with gallic acid – diet GAL – at the inclusion level of 0.032 g/100 g of DM) and fermented in batch for 24h. The formulation and the inclusion levels of the diets were the same as of a previous in vivo trial. At the end of the experiment, the rumen liquor was analysed to evaluate the potential effects of vescalagin and gallic acid on rumen microbiota, FA and DMA profile. Data for FAME and DMA determined by mass spectrometry and microbial relative abundance at genus level determined by high-throughput sequencing, were processed by GLM of SAS. The genera Anaerovibrio, Bibersteinia, Escherichia/Shigella, Streptococcus and the relative abundance of the genus Pseudobutyrivibrio increased with CHT compared to the other feeds while the genus Arcobacter decreased. Furthermore, a slight decrease in the relative abundance of the genus Treponema was observed in GAL fermenters compared to VES fermenters. Changes in microbial profile were not so substantial to induce variations in FA profile. In contrast, the presence of CHT extract, VES and GAL in the basal diet modified the concentration of several DMA. At 24 h DMA 12:0, DMA 13:0, DMA 14:0, DMA 15 iso, DMA 18:0 and DMA 18:1 trans11 were lower in C fermenters than in the others (p≤.05). Results showed that VES and GAL did not exert singularly strong effects on microbiota. Hence, the antimicrobial efficiency of CHT may be due to the overall composition of the tannin extract.