Concentration of phycocyanin with osmotic membrane distillation: influence of temperature, extraction solution concentration and system design

Phycocyanin is a pigment-protein complex produced by some species of microalgae that is gaining increasing attention because of its characteristics. Studies have in fact highlighted its various features such as: antioxidant, anti-inflammatory, anticancer, and neuroprotective properties. Moreover, they also found applications in food and in cosmetic industries. However, its use is limited by some factors such as its sensitivity to temperature, pH, and light exposure. The aim of this study is to investigate the feasibility of phycocyanin concentration by osmotic membrane distillation (OMD), an innovative process well suited for sensitive substances, such as phycocyanin, since it does not require the application of hydraulic pressure or high temperatures. Preliminary tests were carried out in a diffusion cell to analyze the membrane permeability and the water flux and better understand the influence of different driving forces (temperature and extraction solution concentration). Degradation tests were performed at 35°C, 45°C, 55°C to analyze the effect of heat on phycocyanin, proving the substance sensitivity to medium-high temperatures. The same temperatures were used to perform OMD tests with phycocyanin and 4 M CaCl2 extraction solution. The measured fluxes were compared to modeled one, and the presence of fouling phenomenon was highlighted. Concentration and purity of phycocyanin were examined, during and at the end of tests. The results showed the possibility of concentrating phycocyanin at 35°C and 45°C with difference in final product quality: the purity index at 35°C showed an increase in value, while at 45°C a decrement if purity was observed. Organic carbon content measurements confirmed the effectiveness of the process: no phycocyanin transfer occurred between feed and extraction solutions. Finally, experiments were carried out in a bench scale system at 35°C and 45°C and the results were compared to the ones obtained in the diffusion cell. Measured fluxes depicted the comparability of the two systems, while phycocyanin final concentrations showed a discrepancy; in fact, the bench scale system showed no concentration. This behavior was linked with the presence of pumps, that led to phycocyanin mechanical degradation.