Phenolic content and biological activity of extracts of blackcurrant fruit and leaves

•Blackcurrant leaves and fruits are a rich source of polyphenols.•Blackcurrant polyphenols practically do not undergo degradation during storage.•Blackcurrant extracts exhibit high antioxidant activity in relation to biomembrane.•Blackcurrant polyphenols bind to the membrane surface, without altering its structure.

The studies were designed to determine the polyphenolic composition and biological activity of extracts from fruit and leaves of blackcurrant in relation to biological and lipid membranes. A detailed quantitative and qualitative analysis of extracts was conducted, using the UPLC-DAD and UPLC-PDA–Q/TOF-MS methods. Furthermore, stability of the phenolic content in the extracts was determined using the Folin–Ciocalteu method. The antioxidant activity of the extracts in relation to the membrane of erythrocytes and lipids extracted from red blood cell membranes (RBCL) exposed to chemical oxidizing agents (AAPH) was determined, and the effects of blackcurrant extracts on the properties of the membrane of erythrocytes and liposomes (DPPC and RBCL) were examined. Antioxidant activity of the extracts was studied fluorometrically, while effects of the extracts on the properties of membranes were examined using calorimetric, IR spectroscopy and fluorimetric methods. In particular, the effects of the extracts on packing order, membrane fluidity and the main phase transition temperature were determined. Additionally, the affinity of extracts to organic or aqueous media was determined on the basis of their partition coefficient between octanol and phosphate buffer. The results showed that the tested extracts are rich sources of polyphenols, primarily from the group of flavonoids; in leaves flavonols dominate, while in fruit anthocyanins dominate. Their polyphenolic content was quite stable and only slightly changed within 12 months. The substances used markedly protect the membranes against oxidation and to varying degrees modify properties of the hydrophilic regions of membranes. They localize mainly in the area of lipid polar heads of membrane, changing their arrangement, which is consistent with their disclosed hydrophilic character. Due to the rich polyphenolic composition and high antioxidant activity, extracts from the leaves and fruits of blackcurrant protect the organism or food products from the harmful effects of free radicals. In addition, they slightly change the properties of biomembrane lipids and lipid vesicles once they incorporate these extracts. This kind of knowledge is not only of pro-health importance, but can also be used in the food, pharmaceuticals or cosmetics industry, for designing liposomal structures as carriers of drugs, dietary supplements and extracts as biologically active substances.