Sustainable processing of microalgae protein: Design of biphasic partitioning systems based on natural deep eutectic solvents for C-phycocyanin recovery from model aqueous solutions

The development of sustainable protein sources is imperative for addressing the global challenge of food/feed security. Microalgae, which may be sustainably cultivated, are a promising source of proteins, gaining a progressive acceptance among consumers. The purpose of this work is to study the recovery of the protein C-phycocyanin from the microalga Arthrospira platensis (Spirulina), using a biphasic extraction system composed of sustainable solvents. The extraction system studied involves a feed phase, consisting of an aqueous salt solution and the target protein, and an extracting phase composed of a Natural Deep Eutectic Solvent (NADES) with affinity to the target protein. The performance of a specific NADES depends on the characteristics of the components of the NADES, in terms of its hydrophobicity/hydrophilicity balance, aiming the highest possible partitioning coefficient towards C-phycocyanin. It is also important to assure that the NADES phase selected presents a moderate viscosity and leads to a stable interface when in contact with the aqueous feed phase (i.e., presenting a measurable interfacial tension). In this work, after an extensive screening work of more than 71 combinations, the most overall performing combination is presented. This system shows a high partitioning coefficient of 29.4 ± 0.3 and an extraction yield of 99 % for C-phycocyanin (C-PC), demonstrating that the salting-out effect of the phosphate buffer and the hydrophobic character of NADES play a key role in this protein partitioning and recovery.