Experimental study of microorganism disruption using shear stress

There has been a broad spectrum of theoretical and experimental works on microorganism disruption methods undertaken in the past. However, there is a lack of understanding regarding the actual reasons for microorganism disruption using ultrasound and whether it is caused by shock or shear. In the case of shear stress, which is the focus of this paper, analysis of the intense turbulent flow region of an in-house built shear apparatus combined with the experimental results demonstrated that when the energy dissipation rate in the turbulence region is high, and the size of the eddy is smaller than the size of the cell, the likelihood of yeast disruption is high. The mechanical properties of yeast cells combined with the calculated energy dissipation rate were used to evaluate the yeast disruption efficiency (log reduction). The results show that the shear apparatus can efficiently and effectively disrupt S. cerevisiae at different treatment times, suspension temperatures and rotor speeds. The experimental work suggests that maximum yeast log reduction was achieved when the maximum power dissipation of 2.095 kW was recorded at 10,000 RPM, while suspension temperature was controlled below 35 °C. The corresponding shear stress at 10,000 RPM was 2586.2 Pa.