Bead milling and ultrasonication as scalable techniques for cell disruption of Chlorella vulgaris

This study investigates the effectiveness of bead milling and ultrasonication for cell disruption and release of soluble compounds on C. vulgaris suspensions. Bead milling and ultrasonication were performed in semicontinuous mode, both on suspensions made from fresh algal paste and from lyophilized microalgae, to study the effect of starting material. Whereas bead milling resulted in complete cell disruption, ultrasonication only disrupted 74–84% of the C. vulgaris cells, as quantified by cell counting. For both treatments, cell disruption followed first order kinetics described by a fractional conversion model. No differences in disruption rate were observed between both techniques, only in the final degree of disruption. The release of soluble carbohydrates, proteins and pigments followed the same kinetics as for cell disruption. Even though preventive cooling measures were implemented, the occurrence of local high temperatures during ultrasonication led to protein aggregation and pigment degradation for treatment times longer than 45 min, while this was not observed for bead milling. Finally, the difference in starting material (fresh algal paste vs. resuspended lyophilized powder) only had a minor impact on the initial degree of disruption, but there was no significant effect on the final degree of disruption. While both bead milling and ultrasonication are scalable disruption techniques, bead milling is the most favorable technique for disruption of microalgal cells with a tougher cell wall like C. vulgaris , due to the higher effectiveness to achieve full cell disruption.