This antitrypsin activity assay is important because it measures the ability of a sample (e.g., plant extract) to inhibit the proteolytic enzyme trypsin, which is crucial in many biological and industrial contexts (e.g., therapeutic enzyme modulation, functional food ingredient evaluation). The method uses BApNA, a chromogenic substrate that releases a yellow-colored product (p-nitroaniline) upon hydrolysis by trypsin. By comparing absorbances of control vs. sample, one can calculate the percentage inhibition of trypsin activity. Tris-HCl buffer is used instead of phosphate buffer to avoid unwanted buffer-catalyzed BApNA hydrolysis, ensuring reliable and accurate measurement.