The need for protein is increasing due to population growth and climate change. Microorganisms represent one of the most promising new sources. But protein production involves obtaining a concentrated extract before atomization or precipitation. However, after a cell lysis stage leading to complex extracts, it is necessary to purify the proteins before concentrating them. Depending on the micro-organism, the co-extracted molecules may be polysaccharides or pigments such as chlorophyll. When microalgae are lysed, co-extracted pigments in complex form a layer on the membrane surface, totally altering selectivity and reducing flux. Membranes with a molecular weight cut-off ranging from 10 kDa to 500 kDa showed identical retention rates. A microfiltration step eliminates some of these complexes, but a precipitation step proves more effective, increasing flux by a factor of two. Tests carried out with a 10 kDa membrane showed that it was then possible to obtain two fractions, one enriched with phycocyanin and the other with white proteins. These tests were carried out in a stirred cell, and performance should be improved with tangential filtration membranes.
In the case of bacteria, lysis leads to co-extraction of polymers such as heteropolysaccharides and DNA. Permeate fluxes obtained are much higher than with microalgae, but analytical results show that these membranes lead to the concentration of proteins and DNA.
The results confirm that membrane processes are particularly well suited to the concentration of proteins, as in the case of plants, but that for their purification, control of hydrodynamic conditions is essential.