Method for producing product by cells, method for purifying product produced by cells, method for suppressing decrease in membrane permeability of product produced by cells, system for producing product by cells, and system for purifying product produced by cells

A system for producing a product by cells, the system comprising:

• a culture vessel for culturing cells;
• a porous membrane for filtering a cell broth to obtain a product by the cells;
• a pump for feeding the cell broth from the culture vessel to the porous membrane;
• and
• a controller configured to control the pump such that a shear stress due to a flow of the cell broth on a liquid contact surface of the porous membrane is set to 4.0 N/m2 or less,
• wherein the liquid contact surface has at least any one selected from the group consisting of an opening ratio of 57.5% or less, a pore diameter having a coefficient of variation of 0.5 or less, and a ratio of pore diameter/fiber diameter of 1.3 or less, and
• the liquid contact surface has at least any one selected from the group consisting of a structural anisotropy of 0.97 or more and 1.03 or less and a ratio of long pore diameter/short pore diameter of 1.8 or less.