Effects of sea buckthorn and black currant extracts on the growth, acid production, and antagonism of bifidobacteria

Plant polyphenols have recently been recognized as promising new-generation prebiotics. However, the concentrations and profiles of polyphenols vary significantly among different plants, so the effects of their extracts on probiotic strains are also highly variable. This study assessed the effects of ethanol and supercritical fluid extracts of black currant and sea buckthorn on the growth of bifidobacteria and their antagonism against intestinal pathogens. Extracts of black currant and sea buckthorn were obtained using reflux ethanol extraction or supercritical fluid extraction. Total phenols in the extracts were determined by the Folin-Ciocalteu colorimetric method. Individual phenolic compounds were identified by UV-Vis spectroscopy. Effects of the extracts on bifidobacteria and the intestinal pathogens Bacillus cereus and Staphylococcus aureus were evaluated in monoculture. Antagonism of bifidobacteria against the pathogens was evaluated in coculture in the media with various ethanol extracts. Concentrations of organic acids were determined using HPLC. Phenolic components of the berries had stimulated, neutral, or negative effects on probiotic growth and organic acid production, depending on the type of raw material and the extraction method. Bifidobacterium adolescentis and Bifidobacterium longum were the most sensitive to, and strongly inhibited by, the extracts, while no pronounced growth-stimulating effect was observed for any of the studied bifidobacteria strains. Additionally, the effect of total phenolic concentrations in the extracts on the strain growth was evaluated by diluting the native extracts. Minimum inhibitory concentrations in the ethanol extracts for bifidobacteria ranged from 30 to 140 μg GAE/mL, while those in the supercritical fluid extracts were lower (13–32 μg GAE/mL). The sea buckthorn supercritical fluid extract stimulated Bifidobacterium bifidum growth, while the ethanol extract of sea buckthorn and the supercritical fluid extract of black currant stimulated the growth of Bifidobacterium breve and B. longum subsp. infantis. B. cereus was not sensitive to changes in total phenolic concentrations. The minimum inhibitory concentration of total phenols for S. aureus was the lowest (7 μg GAE/mL) in the supercritical fluid extract of sea buckthorn. The extracts had mostly neutral or positive effects on lactic and acetic acids production by bifidobacteria. The greatest increase in acid concentrations was observed for B. breve in the medium with black currant ethanol extract. The greatest suppression of pathogen growth was achieved by a combination of B. breve with either of the ethanol extracts. The results demonstrate that black currant and sea buckthorn extracts are highly selective prebiotics that exert different effects on the antagonism of bifidobacteria against pathogens. The study revealed the most effective combination of the bifidobacteria and berry extracts against the pathogens, as well as the most effective symbiotic composition.