Pretreatment of algal and cyanobacterial biomass for high purity phycocyanin production

Abstract

Phycocyanin is a water-soluble, blue-colored phycobiliprotein, mainly found in cyanobacteria and red algae. Major commercial interest on phycocyanin exists as an important ingredient for food, pharmaceutical and cosmetics sectors. However, dedicated and efficient methods of extraction optimized for different organisms are lacking. In this study, wet and freeze-dried biomass samples from several cyanobacteria (including a local isolate) and a red microalga species were pretreated with sonication, mortar and pestle, freeze-thaw cycling and bead-beating. High concentration yielding phycocyanin extracted from Phormidium sp., Synechocystis sp., Desertifilum tharense, Nostoc sp. and Galdieria sulphuraria were purified by ammonium sulfate fractionation combined with acetate buffer elution. Bead-beating has been found to be the most successful pretreatment for the extraction of phycocyanin. Phycocyanin from Synechocystis sp. and Phormidium sp. were further purified with anion exchange chromatography. Overall, food grade phycocyanin extraction has been achieved for all biomass samples except Scytonema sp. The highest phycocyanin purity with a higher observed value compared to literature was obtained from Synechocystis sp. Furthermore, the effect of various stress conditions (light, salinity, and hydrogen peroxide) on biomass growth and phycocyanin production for Synechocystis sp. was investigated after PC extraction with bead-beating. As an alternate method to salting-out, chitosan/activated charcoal was applied as purification step. Antioxidant activities of purified phycocyanin were tested via 1,1-diphenyl-2-picrylhydrazyl (DPPH) activity assay and compared to L-ascorbic acid (vitamin C). In average, ammonium sulfate precipitation gave higher antioxidant activity than activated charcoal and chitosan purification and obtained PC showed lower antioxidant activity than L-ascorbic acid for both purification methods.