Insight into the Phenolic Composition of Cabernet Sauvignon Grapevine Berries During Fermentation-Towards the Application of Winery By-Products for Antibacterial Purposes.

Background: Wine production generates significant amounts of grape marc, which can serve as a potential source of bioactive compounds, including polyphenols.

Objectives: In this study, we aimed to investigate the polyphenol content of skin and seeds separated from grape marc, and test their extracts against two significant bacteria, Listeria monocytogenes (LM) and Staphylococcus aureus (SA).

Methods: A comprehensive analysis of the phenolic composition in the skin, seeds, and juice/wine derived from Cabernet Sauvignon grape berries was conducted over an 18-day fermentation period. High-performance liquid chromatography was performed to identify and quantify the main flavan-3-ols, flavonols, anthocyanins, and stilbenes. In addition, the total phenolic content (TPC) was determined by the Folin-Ciocalteu method.

Results: The TPC of both seeds and skins significantly decreased over time. In parallel, the TPC in the wine gradually increased, indicating a release of phenolic compounds into the wine. We found that the TPC in seeds was consistently higher than in the skin at all examined time points. The main flavonoids in seeds were flavan-3-ols (catechin and epicatechin), while anthocyanins (delphinidin-, cyanidin-, petunidin-, peonidin-, and malvidin-3-O-glucoside) were the predominant ones in skins. Crude seed and skin extracts enriched in phenolics were prepared, of which only the crude seed extract was proven effective against LM and SA. Following the time-kill assay, our findings revealed that the minimal bactericidal concentration of the crude seed extract against LM was 5.02 mg/mL after 12 h incubation, demonstrating the eradication of the living bacterial cell number by ~6 log. A 24 h exposure time was required for complete inactivation of SA, but a lower concentration was sufficient (2.54 mg/mL).

Conclusions: Grape waste remains a valuable source of polyphenols, with grape seeds, in particular, exhibiting significant antimicrobial activity against certain foodborne pathogens.