Optimum pH and pH stability of purified polygalacturonase from grapes. The effect of pH on enzyme activity was determined at 40°C using 0.05M of various buffers. For pH stability, the enzyme was diluted with buffers of pH range (2.5-7.0) and incubated at room temperature for 1 h and determined the residual activity at 40°C. The data is representative of mean of three experiments.