Influence of in vitro simulated gastroduodenal digestion on the antibacterial activity, metabolic profiling and polyphenols content of green tea (Camellia sinensis)

The antistaphylococcal activity as well as the metabolic profiling and polyphenols content of green tea (Camellia sinensis) before and after in vitro simulated gastric, duodenal and gastroduodenal digestion were investigated. Gastric and duodenal digested samples showed antistaphylococcal activity, whereas gastroduodenal digested samples did not show any antibacterial activity. Metabolite analysis, carried out using an explorative untargeted NMR-based approach and a RP-HPLC-PAD-ESI-MSn method, showed that green tea polyphenols are stable under gastric conditions. Duodenal digested sample maintained the antibacterial activity, even if some polyphenols are widely degraded. Epicatechin 3-gallate, under duodenal digestive conditions, is hydrolyzed to produce epicatechin, whereas epigallocatechin 3-gallate reacts with digestive enzymes and a galloyl-high molecular weight derivative is produced. Gastroduodenal digestion results in degradation of polyphenols, especially gallocatechins, considered the main responsible for the antibacterial activity. These results explain the loss of activity of gastroduodenal digested samples and why in vivo green tea has neither protective nor therapeutic effects against intestinal and systemic bacterial infections.