Freeze-thaw-assisted aqueous two-phase system as a green and low-cost option for analytical grade B-phycoerythrin production from unicellular microalgae Porphyridium purpureum

Abstract

Microalgae are promising alternative sources for natural phycobiliprotein production since they grow rapidly and can be cultured on a large scale. However, the overall economic viability of analytical grade phycoerythrin production from microalgae is limited by the high cost of the pretreatment required to break down the cell wall, as well as the expensive reagents and equipment used during purification. This study developed a novel extraction and purification process to recovery B-phycoerythrin (B-PE) in a freeze-thaw-assisted aqueous two-phase system (FT-ATPS) from Porphyridium purpureum. The effects of culture strategy, extraction method and purification factors on B-PE production were studied systematically. The results revealed that low light induced B-PE synthesis, whereas hindered the growth. The stepwise light supplement strategy alleviated the growth limitation under low-light conditions and increased the final B-PE production, up to 182.1 ± 4.1 mg/L (increasing by 73.1 %). Compared with the traditional electricity highly-consumed ultrasonication method, the green freeze-thaw method could extract B-PE without damaging the cell structure and save much more power (>98 %), and the extraction rate reached the highest when frozen at −80 °C. The purity and concentration of B-PE in crude extract were proved to have a significant effect on ATPS purification, and the higher the former, the better the latter. A total production cost of 0.045 $/mg (decreasing by 96.2 %) and purity of 5.6 ± 0.2 (A545/A280) for analytical grade B-PE production were achieved by FT-ATPS based on 4 % polyethylene glycol (PEG2,000) and 20 % ammonium sulfate. Relative to the conventional method of phycoerythrin production, the method developed herein has greater safety, lower cost, and more environmental benefits, which can be function appropriately in the expensive purification of analytical grade phycobiliproteins.