2.2.1 Extraction of crude enzyme solution
A total of 10 mL of deionized water was preheated at different temperatures for 10 min, and 1 g of the fresh leaves was accurately weighed and added to the preheated water. After 10 min of heat treatment, the leaves were immediately removed and placed in a 4 ℃ ice bath. After the ice bath, 30 mL 0.5 M acetic acid buffer was added to the leaves, which were fully ground and centrifuged at 7370 × g at 4 ℃ for 20 min. After centrifugation, the supernatant was taken and placed on ice for storage.