Quantitation of polyphenolic content and determination of antilisterial activities of grapes and vinification byproducts

Four grape varieties (two red and two white) –cultivated in the Greek islands– were studied in respect to their total polyphenolic content (TPC) and quantization of their main polyphenols. More specifically, berries, seeds, stems and pomace samples were examined, indicating that seeds contain high concentration of flavan-3-ols and respective derivatives, while pomace and stems contain considerable amounts of flavonoids. stilbenes and phenolic acids. In particular, stems were found to possess high trans-resveratrol and ε-viniferin content. Subsequently, the in vitro antilisterial activities of these extracts were evaluated.

In addition, the MICs (minimum inhibitory concentrations) of the most potent extracts were comparatively assessed on a Malthus apparatus, using either a plate count technique or an innovative-automated technique that combines conductance measurements with the common dilution method. The antilisterial assays indicated that seeds and stems of red grape varieties possess the most significant activity, exhibiting MIC values 0.26 and 0.34mg/ml respectively. Thus they represent an inexpensive source of natural antibacterial substances which may be used in food systems to prevent the growth of foodborne bacteria and/or extend the shelf life of the processed food.