Substrate concentration: In the context of a detergent, the substrate would be the concentration of stains present on the surface being cleaned. Generally, up to a certain point, increasing substrate concentration can enhance the rate of enzymatic reaction and thus improve cleaning ability. This is because more substrate molecules are available for the enzymes to act upon. However, there comes a point of saturation where increasing substrate concentration further does not lead to a proportional increase in enzyme activity. At this point, all enzyme active sites are occupied, and further increase in substrate concentration won't result in a faster reaction rate. Therefore, the cleaning ability of the enzyme-added detergent may plateau beyond this saturation point.