Proanthocyanidins: Target Compounds as Antibacterial Agents

TLDR

Grape seeds, a plentiful wine‑production byproduct, are a cheap source of pharmacologically active compounds, yet studies report inconsistent and generally weak antibacterial activity. This study aimed to assess the antibacterial efficacy of grape seed extracts and chromatographically identify the active fractions. Microwave‑assisted extraction was optimized for maximal preconcentration, and HPLC‑MS identified proanthocyanidins and glycosides, with isomer numbers estimated by a novel equation. Extracts inhibited 10 Gram‑positive and Gram‑negative strains; fractionation revealed proanthocyanidins P2, P3, P4, P2G, and P3G as potent antibacterial agents, while monomeric flavonoids showed only moderate activity.

Abstract

Grape seeds accumulate in huge quantities as byproduct during wine production and are therefore a cheap source for pharmacologically active agents. However, studies prove poor antibacterial activity, and results of analyses are sometimes contradictory. The aim of this study was, thus, to determine the antibacterial activity of grape seed extracts with special focus on the chromatographic characterization of active fractions. In the course of these investigations, extraction protocols were optimized so that microwave-assisted extraction (MAE) guaranteed highest preconcentration efficiency. Proanthocyanidins, monomeric flavonoid aglycones, as well as some of their glycosides could be identified within yielded extracts via high-performance liquid chromatography−mass spectrometry (HPLC−MS). By that means the coherence number of possible isomers of procyanidins was approximated by a newly developed equation. As far as antibacterial activity determined via screening tests is concerned, the extracts generally have been found to be positively responsive toward 10 different Gram-positive and Gram-negative bacteria strains. After fractionation of the raw extracts, proanthocyanidins P2, P3, P4 and gallate esters P2G and P3G (P = proanthocyanidin consisting of catechin and epicatechin units, n = oligomerization degree, G = gallate ester) were determined as active antibacterial agents toward 10 different pathogens. Only moderate activity was found for monomeric flavonoid fractions.