## 5 Conclusions and Future Perspectives  
To solve the upcoming protein shortage, new alternatives to animal protein must appear, reducing the environmental consequences of current protein production processes. Microalgae biorefinery is a bright answer to this problem because it is an excellent protein source (around half of the microalgae dry weight is protein, containing all nine essential amino acids). At the same time, these microorganisms can reduce atmospheric CO\({}_{2}\). However, the recovery of proteins from the microalgae matrix is complicated, and it is usually considered the bottleneck of the process. For protein recovery, multiple available techniques allow protein obtaining, and depending on their fundamentals, different purity levels will be attained. All the techniques discussed in this review have different advantages, but they also present some drawbacks. For example, despite precipitation being a straightforward approach, still low yields are obtained, while chromatography provides high efficiencies, but it is challenging to scale up the process. The solvent extraction method is one of the most employed, yet organic solvents go against the sustainability desirable for the process. In this context, ILs, and especially DESs, have been revealed as a greener alternative for protein extraction due to their excellent physicochemical properties that enable an efficient and environmentally friendly recovery.  
There is no doubt that biodegradable solvents will be the key to new green processes for obtaining many bioactive compounds. Nevertheless, more efforts are needed to investigate ILs and DESs limitations, and consequently, the ATPS approach. In particular, from our view, forthcoming studies and developments should focus on: (I) preparing more efficient DESs or NADESs to extract protein from microalgae, as they stand as a more environmentally friendly protein source; (II) recovering the proteins sustainably from the solvent, paying attention to how to reuse the solvents employed in further extraction procedures; (III) fully understanding the nature and behavior of DESs and ATPS systems, in order to obtain more selective solvents for the analyte to be separated. Shedding light on these items would provide incredible advances not only for microalgae protein extraction but also in separation science.  
Conceptualization, S.B., P.A.G.-E. and B.C.-G.; analysis of the information, investigation, and writing of the paper D.M., E.M.R., S.B., P.A.G.-E. and B.C.-G.; writing of the paper, D.M. and E.M.R.; review and editing S.B., P.A.G.-E. and B.C.-G. All authors have read and agreed to the published version of the manuscript.  
This research was funded by MICINN-FEDER (projects PID2020-113544 RB-I00 and CTQ2017-84006-C3-1-R). The authors also thank the Regional Government of Castilla y Leon and the EU-FEDER (CLU 2017-09). [PERSON] would like to thank the \"Ministerio de Ciencia, Innovacion y Universidades\" for her doctorate scholarship (PRE2018-083845). [PERSON] would like to thank the \"Ministerio de Universidades\" for his FPU grant (FPU20/02086).  
Not applicable.  
The authors would also thank [PERSON] for Figure 1 illustration.  
The authors declare no conflict of interest.