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 to evaluate their antioxidant capacity. R-phycoerythrin and R-phycocyanin were isolated by gel filtration with Sephadex G-200 and further purified by RP-HPLC. Phenolic compounds were extracted by solvents of different polarity. The Folin-Ciocalteu method was used to determine the total phenolic content (TPC), while 1, 1-diphenyl- 2-picrylhydrazyl (DPPH) radical scavenging and ferric reducing antioxidant power (FRAP) assays were used to measure 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 5.42, while R-phycocyanin had displayed 16% yield at a purity ratio A(615) to A(280) of 3.95. The purified R-phycoerythrin exhibited better antioxidant activity (IC50 = 7.66 +/- 0.81 mu g/mL) and 54.81 +/- 0.31 mg GAE/g extract, compared to R-phycocyanin extract and BHT for DPPH scavenging and FRAP assays, respectively. SDS-PAGE of purified R-phycoerythrin and R-phycocyanin proteins displayed a clear narrow single band with molecular weight at 20.5 and 17.6 kDa, respectively. The 100% methanol-soluble extract had the highest phenolic compounds content, 80.97 +/- 0.53 mg GAE/g extract compared to phenolic content in other organic solvents used for extraction. The 100% methanol extract with highest phenolic content was evaluated with antioxidant activity assays. These assays showed that the 100% methanol extract with high phenolic content had the effective DPPH radical scavenging and ferric reduction potential (IC50 = 30.82 +/- 0.92 mu g/mL extract) and 37.81 +/- 0.04 mg GAE/g extract, respectively. B. atropurpurea has higher antioxidant property in positive correlation with total phenolic content however, studies have justified that the phenolic compounds were not the only contributor to the antioxidant capacities of this red alga. B. atropurpurea has abundant clusters of R-PE and R-PC, attached to the thylakoid membranes were effectively contributed to the antioxidant activities. Studies shown, the purified R-PE and R-PC exhibited better antioxidant property than phenolic compounds and synthetic antioxidant.