POLYPHENOLIC SCREENING AND ANTIOXIDANT ACTIVITY OF GRAPE POMACE EXTRACTS OF ROMANIAN WHITE AND RED GRAPE VARIETIES

Due to its valuable organic compounds, grape pomace represents a useful resource for value-added food products. Aiming at the extraction of the phenolic compounds from the pomace of Romanian white and red grape varieties, the ethyl alcohol: water =1:1 solvent and the ultrasonication were tested, based on the results of our preliminary screening tests. Significant differences among the pomaces obtained from different grape varieties were determined in terms of their phenolic content. The total polyphenols content (TPC) and the total flavonoid content (TFC) of grape pomace extracts decreased as follows: Negru de Drăgășani > Fetească Neagră > Fetească Albă > Tămâioasă Românească. The red varieties (Fetească Neagră and Negru de Drăgășani) were the richest in total phenolics and total anthocyanins, respectively. The presence of the different phenolics varied according to the grape variety. Thus, catechin was the most abundant phenolic compound determined in the pomace extract of Negru de Drăgășani variety. The antioxidant activity of extracts obtained from grape pomace showed that Negru de Drăgășani had the highest antioxidant activity due to its high level of polyphenols, followed by Fetească Neagră, Fetească Albă, and Tămâioasă Românească varieties, respectively. A high amount of bioactive polyphenolic substances, such as myricetin, resveratrol, and vanillic acid, was also determined in the pomace of Negru de Drăgășani extract. These results emphasized the potential of Negru de Drăgășani variety to be further exploited for nutritional and functional applications. The pomace from the Fetească Albă variety will be further investigated due to its higher amount of kaempferol, a compound with proven beneficial biological activities. Overall, these results show that the pomace obtained from the four Romanian white and red grape varieties could be successfully valorized to both contribute to the sustainability of wine making and innovation in the economic sectors needing the added value of the phenolic compounds with antioxidant activity.