The supernatant was used as the crude enzyme extract and stored at 4 °C for the determination. 0.5 mL of enzyme extract was incubated with assay medium containing 3.5 mL of 100 mmol/L sodium borate buffers (pH 8.7) and 1 mL of 10 mmol/L L-phenylalanine as substrate at 37 °C for 1 h.