The study of the chemical composition and comparative analysis of the total antioxidant capacity of blackberry (Rubus plicatus Weihe & Nees) leaves and fruits

Aim. To study the chemical composition and comparative analysis of the total antioxidant capacity of blackberry (Rubus plicatus Weihe & Nees) leaves and fruits. Materials and methods. The content of phenolic compounds, anthocyanins, flavonoids, and hydroxycinnamic acids was determined by the spectrophotometric method, whereas organic acids were determined by the alkalimetric method; the antioxidant capacity of the extracts obtained was evaluated by the potentiometric method. Results. The total antioxidant capacity of blackberry leaves and fruits was 240.44 and 71.20 mmol-equiv./mdry weight, respectively. Comparing the total antioxidant capacity of blackberry leaves and fruits at same molar concentration (0.03 mol/L), it was equal 26.00 and 35.60 mmol-equiv./mdry weight, respectively. The total content of phenolic compounds was 46.02 and 10.00 mg/mL calculated with reference to gallic acid, catechins – 24.22 mg/mL calculated with reference to epigallocatechin-3-O-gallate (absent in fruits), anthocyanins – 9.60 mg/mL calculated with reference to cyanidin-3-glucoside, flavonoids – 16.54 mg/mL calculated with reference to rutin (absent in fruits), hydroxycinnamic acid derivatives – 18.00 mg/mL calculated with reference to chlorogenic acid (absent in fruits) and organic acids – 22.40 and 22.20 mg/mL calculated with reference to citric acid in blackberry leaf and fruit extracts obtained during the sequential exhaustive extraction, respectively. The correlation analysis showed that there was a very high positive dependence of the antioxidant capacity and the total content of phenolic compounds, catechins and anthocyanins, flavonoids, and hydroxycinnamic acid derivatives in blackberry leaf and fruit extracts. Conclusions. The total antioxidant capacity of R. plicatus leaves was higher than that of its fruits; however, when compared at the same molar concentration, the fruits exhibited a greater antioxidant capacity. The analysis of biologically active substances and the antioxidant capacity of R. plicatus extracts demonstrated that the aqueous extract contained a significant amount of biologically active compounds, as well as exhibited a pronounced antioxidant capacity. The quantification showed that catechins were the main group among the phenolic compounds in R. plicatus leaves, while anthocyanins predominated in fruits. The correlation analysis revealed a strong positive linear relationship between the antioxidant capacity and the content of phenolic compounds, flavonoids, catechins and anthocyanins in the case of fruits, while the weakest correlation was observed for organic acids. These results can be used to develop optimal technologies for producing drugs based on R. plicatus leaf and fruit extracts