Ultrasound-Assisted Extraction and Assessment of Biological Activity of Phycobiliprotein-Rich Aqueous Extracts from Wild Cyanobacteria (Aphanizomenon flos-aquae)

Cyanobacteria are photosynthetic microorganisms that are considered as an important source of bioactive metabolites, among which phycobiliproteins (PBPs) are a class of water-soluble macromolecules of cyanobacteria with a wide range of applications. Massive proliferation of cyanobacteria can lead to excessive surface water blooms, of which removal, as a management measure, should be prioritized. In this study, the utilization of wild cyanobacteria biomass (Aphanizomenon flos-aquae) for extraction of phycobiliproteins is reported. Extraction of phycobiliproteins by conventional methods, such as homogenization, freeze-thaw cycles, and solid-liquid extraction, were optimized prior to ultrasound-assisted extraction. Standardization of ultrasonication for different parameters, such as ultrasonication amplitude (38, 114, and 190 μm) and ultrasonication time (1, 5.5, and 10 min), was carried out using a central composite design and response surface methodology for each of the primary techniques. A substantial increase on the individual and total phycobiliprotein yields was observed after ultrasonic treatment. The highest total PBP yield (115.37 mg/g of dry weight) was observed with samples treated with a homogenizer (30 min, 30 °C, and 1 cycle) combined with ultrasound treatment (8.7 min at 179 μm). Moreover, in vitro antioxidant capacity was observed for the obtained extracts in the Folin-Ciocalteu and ABTS^* + assays. In addition, a cytotoxic effect against C6 glioma cells was observed for A. flos-aquae PBPs. Conclusively, wild cyanobacteria could be considered as an alternative feedstock for recovery of PBPs.