## 3 Results
applied for the blackberry samples that have been subjected to the same types of extractions, observing that a good anthocyanin extraction yield was achieved for the 50-50% mixture. For the determination of the antioxidant activity of grape skin and blackberry extracts (Table 1), the ABTS method was used. The assay was based on the relative ability of antioxidants to scavenge the cation radical ABTS\(\bullet^{+}\)[37]. The highest TAC (umol Trolox g\({}^{-1}\)GSE and/or BE) value was observed in the blackberry extract (264.27). Compared to methanol extracts, ethanol extracts showed higher antioxidant activity (264.27 toward 189.30 for blackberry and 216.19 toward 168.26 for grape skin). Equivalents of standards were calculated on the basis of standard regression line for gallic acid (R\({}^{2}\) = 0.9973) and the standard regression line of Trolox was used to calculate TEAC (Trolox equivalent antioxidant capacity) (R\({}^{2}\) = 0.9921). Percentage of inhibition was high in the case of both grape skin extract (Figure 7) and blackberry extract (Figure 8). The TAC value can be considered as a stoichiometric number that can be correlated with a Trolox value of one. Indeed, many studies reported TAC values that depended not only on the phenolic content, but also on the phenolic compounds type and the reaction mechanisms [38]. This may suggest that TP can not be singularly used to explain the determined antioxidant activities of the extracts, which are in fact mixtures of various compounds with variable activities. Figure 9 presents the correlations between TP, TA, PC, and TAC as a function of the extraction method. It can be observed that the highest TP values were obtained when 50% ethanol and 80% methanol were used as solvents for blackberries. At the same time, when 80% methanol was used, the TA, PC, and TAC decreased. In the case of black grape skins, the highest values of TP were observed when 80% methanol was used, but with a trade-off regarding the TA, PC, and TAC values. When 50% ethanol was used, the TP was lower, but it was observed increased values for TA, PC, and TAC. Previous studies have reported that the higher phenolic content in the extracts resulted in higher antioxidant activity, which was in agreement with a positive correlation between TP and antioxidant activity [39; 40]. So, in order to obtain the detail correlations between antioxidant capacity and the TPC, the correlation analyses were conducted (Table 3). The significant correlations between the antioxidant properties and TP were found. The TP was highly associated with scavenging ability against ABTS (r = 0.977) for blackberries ethanolic extract. So, the data indicated that the phenolic compounds were considered responsible for effective antioxidant properties. When compared with other methods [41; 42], the developed HPLC method has one major advantage, allowing a proper separation of more anthocyanins from all berries extracts. This separation is also due to the selected extraction methods. Compared with other studies, it was observed that the ethanol and methanol extraction methods improved the antioxidant capacity of the grape skins, from 200 \(\upmu\)M Trolox/g extract [42] to 216 \(\upmu\)M TROLOX/g extract. Additionally, it was observed that the total phenolic content increased from 12.3 mg GAE/g extract to 14 mg GAE/g ethanolic extract and 21 mg GAE/g methanolic extract. Despite there being a lack of information regarding the studied grapes (_Othello_ type), it was demonstrated that they contain important amounts of polyphenols, and further studies should be performed in order to be able to use them as fresh functional foods or fruit-derived products. Figure 9: Correlation between TP, TA, PC, and TAC.