ANTIOXIDANT ACTIVITY AND POLYPHENOL CHARACTERIZATION OF BLACK CURRANT EXTRACT LOADED ALGINATE-INULIN BEADS

Background
Black currants (Ribes nigrum) fruit and leaves are known for their abundance in vitamin C and anthocyanins. Pomaces are promising source of polyphenolics, especially, anthocyanins. Inulin is a soluble prebiotic dietary fibre that can form hydrogel. It is not absorbed or degraded in the upper part of gastrointestinal tract but is broken down by colonic bacteria. Thus, inulin provides extended release of drugs to the colon. Combining alginate and inulin could enhance stability of beads, as alginate can be cross-linked with calcium chloride. Encapsulation of extract in alginate-inulin bead could ensure target drug delivery system.

Objectives
Aim of the study was to select optimal extract to incorporate in alginate-inulin beads and study rheological and pH dependant release properties of drug delivery system.

Materials and methods
Whole berry, berry juice and pomace were extracted with various concentrations of ethanol (96%, 70%, 50%), then solvent evaporated and extract freeze-dried. Polyphenol content characterized using High precision liquid chromatography (HPLC), total phenolic content (TPC) and 1,1-diphenyl-2-picrylhydrazil (DPPH) antiradical activity was determined using UV-VIS spectrometry. Alginate 0.1 g were dissolved in 20 mL water at 80 °C using magnetic stirrer then 20 g or 40 g inulin was added. The 20 mg of extract added to 20 ml of mixture at distinct stages. After gelation beads were formed by crosslinking with 1.5% Calcium chloride. Rheological characterization was done using amplitude and frequency sweep tests, yield point and cross-linking determined. The bead stability and drug release determined at pH 1, 6.8 and 7.4.

Results
The yield of berry products was 64% of juice and 23% pomace, from obtained freeze-dried extract 100 mg was used in analysis. The pomace extract contained the highest yield (0.6 mg gallic acid equivalents/g of extract). The whole berry extract had highest antioxidant activity with IC50 of 0.68 µg/mL followed by juice extract 1.4 µg/mL and pomace extract 2.4 µg/mL. The preliminary data from HPLC analysis showed that although similar compounds were detected in all extracts, the pomaces were the richest in phenolic acids, flavonoids, and anthocyanidins. In addition, ethanol concentration affected the polyphenolic profile of berry extracts. Un-crosslinked gel showed viscoelastic fluid like behaviour as G’’ exceed G’. The beads showed better stability at high strains. Beads containing 20% inulin demonstrated reduced storage and loss moduli and reached the yield point at lower strain values, indicating decreased mechanical strength and structural stability compared to beads with 40% inulin. The beads were pH reactive and showed differing release profiles.

Conclusions
Black currant pomaces are valuable sources of polyphenols. The alginate-inulin beads are pH reactive and need to be analysed further for pharmaceutical applications.