Evaluation of antioxidant properties of phycobiliproteins and phenolic compounds extracted from Bangia atropurpurea

Bangia atropurpurea is a freshwater red filamentous alga. In this study, we report on the recovery yield of purified phycobiliproteins, total phenolic content (TPC) and their antioxidant capacity. B. atropurpurea suspended in phosphate buffer (pH 7.2), saturated with ammonium sulphate and further isolated R-phycoerythrin and phycocyanin from phycobilisome structure by gel filtration with Sephadex G-200. Phenolic compounds extracted by variable polarity solvents to exhibit optimum yield. Folin–Ciocalteu method was used to determine the TPC, while 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and ferric-reducing antioxidant power ( FRAP) assays were used to quantitate the antioxidant activity of phycobiliproteins and phenolic compounds.  B. atropurpurea predominantly contains R-phycoerythrin 54.80 % of the total protein extracted at purity ratio A 562 to A 280 of 4.45 while, phycocyanin displayed 16 % recovery yield at purity ratio A 615 to A 280 of 2.18. The purified R-phycoerythrin exhibited better antioxidant activity than phycocyanin extract and BHT synthetic antioxidant by exhibiting (IC 50% =7.66 ±0.81µg/mL) and 54.74 ± 0.11 mg GAE/1g extract for, DPPH scavenging and FRAP assay, respectively. The sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of purified R-phycoerythrin and phycocyanin proteins have showed apparent single band at molecular weight of 19.6 kDa and 17.5 kDa, respectively. The methanol-soluble extract displayed the utmost TPC, 80.97±0.53 mg GAE/1g extract compared to phenolic content in other organic solvents used for extraction. In accordance with TPC, methanol-soluble extract exhibited as the most effective DPPH radical scavenging and ferric reduction, (IC 50% =14.63±0.79 µg/mL) and 37.79±0.27 mg GAE/1g extract, respectively. The presence of R-phycoerythrin, phycocyanin and phenolic compounds in an array, amplifies the antioxidant property of B. atropurpurea.