Evaluation of mixing effect and shear stress of different impeller combinations on nemadectin fermentation

•Flow field characteristics were evaluated by laser particle image velocimetry system in nemadectin fermentation.•Physiological parameters showed that shear stress seriously affect the mycelium growth and mycelial differentiation.•The higher batch yield of nemadectin reached 1543.27 μg/mL under the radial-axial flow group.•The radial-axial flow impeller combinations were conducive to nemadectin fermentation of Streptomyces cyaneogriseus.