Abstract
Polyphenols belong to the family of secondary metabolites found in plants and mainly in grape berries. They play an important role in the protection of the plant against biotic and abiotic stresses. They have an impact on the organoleptic quality of certain foods such as those from grapes and are mainly known for their beneficial roles for human health. A global study on the phenolic composition and the biological activities (antioxidant, anti-inflammatory and anti-diabetes) of the phenolic extracts of the seeds and skins of three red grape varieties Merlot, Tannat and Syrah at different stages of maturation was carried out during this thesis. Seed extracts contain a higher content of phenolic compounds than skin extracts for all stages of ripening. The phenolic composition differs depending on the stage of maturity and the tissue of the grape berry (seed or skin). The antioxidant activity of the extracts was determined by spectrophotometric tests (DPPH, ABTS and FRAP) and electrochemical parameters. Anti-inflammatory activity was followed by the inhibition of ROS and NO production by stimulated RAW 264.7 cells. Anti-diabetic effect was determined by measuring the inhibition of the enzyme α-glucosidase activity. The biological activities are positively correlated with the content of flavanols and negatively correlated with the content of anthocyanins and stilbenes. The most important biological activities were measured before maturity for all the tests and in the three grape varieties studied.