MF and UF membranes are used for filtration (generally, permeate is the product) as well as concentration techniques (generally, retentate is the product). As the products vary, it is difficult to characterize the membranes by the manufacturers. As an approximation, they test the membranes with water, with predetermined quality, and and the permeate flux rate is published.
Once you take a trial on your actual product on pilot scale, you can extrapolate and approximate the data for various concentrations and feed flowrates and accordingly choose the membrane surface area to suit your process time limitations.