The samples (including apple juice, fermentation liquor during fermentation and apple wine after aging) were centrifuged at 5000 g (4 ?C) for 15 min, and then the supernatants were diluted with sample diluent according to the kit directions. The activities of PME, PL and PG were determined with a PME-ELISA Assay Kit (Shanghai Hengyuan Biotechnology Co., Ltd, Shanghai, China), PL-ELISA Assay Kit (Shanghai Hengyuan Biotechnology Co., Ltd, Shanghai, China) and PG-ELISA Assay Kit (Shanghai Hengyuan Biotechnology Co., Ltd, Shanghai, China) according to the manual, respectively. The absorbance was recorded at 450 nm using a microplate reader (SpectraMax M5, Molecular Devices, LLC., San Jose, America), which was positively correlated with PME, PG and PL activities.
