Method for preparing a protein isolate of the biomass of microalgae of the genus Chlorella, includes: supplying a microalgal biomass produced by fermentation； optionally washing the biomass so as to eliminate soluble interstitial compounds, thermal permeabilization of the biomass at a temperature between 50 and 150° C., for between 10 seconds and 5 minutes； eliminating the thus permeabilized biomass by a solid-liquid separation technique selected from the group consisting of frontal or tangential filtration, flocculation and centrifuging, more specifically multi-stage centrifuging, in order to obtain a soluble fraction； optionally recovering and clarifying the soluble fraction thus obtained by microfiltration in such a way as to remove residual insoluble elements therefrom； ultrafiltration of the soluble fraction on a membrane with a cut-off threshold lower than 5 kDa, preferably between 1 and 5 kDa, in order to produce a soluble protein isolate； then evaporation, pasteurization and atomization of the protein isolate.
