Experiences with a 20 litre industrial bead mill for the disruption of microorganisms

Suspensions of several yeast strains and bacterial species were disrupted in a continuously operating industrial agitator mill of 22.7 litre internal working volume. The influence of agitator speed, flow rate, concentration of microorganisms in the slurry, packing density of glass beads and bead diameter on the disruption process was studied using baker's yeast ( Saccharomyces cerevisiae). Cell disintegration was followed by assaying the appearance of protein and the activities of d-glucose-6-phosphate dehydrogenase [ d-glucose-6-phosphate:NADP + oxidoreductase, EC 1.1.1.49] and α- d-glucosidase [α- d-glucoside glucohydrolase, EC 3.2.1.20] in the soluble fraction. The best operating conditions for the disintegration of baker's yeast with respect to activity yield appeared to be at a rotational speed of 1100 rev/min, a flow rate of 100 litre h −1 and a cell concentration of 40% (w/v). The location of the desired enzyme in the cell is of importance for the choice of bead diameter and packing density of the glass beads. Temperature increase and power consumption during disintegration are also strongly influenced by the bead loading in the mill. With optimized parameters, 200 kg baker's yeast can be processed per hour with a degree of disintegration >85%. The disruption process in the mill was found to be very effective for several yeast species tested, e.g. Saccharomyces cerevisiae, Saccharomyces carlsbergensis, and Candida boidinii. The usefulness of the Netzsch LME 20-mill for the disruption of bacteria species was demonstrated with Escherichia coli, Brevibacterium ammoniagenes, Bacillus sphaericus and Lactobacillus confusus. As expected, the mill capacity for bacterial disruption was significantly smaller than for the yeast. Between 10 and 20 kg per h bacteria may be processed, depending on the organism.