Fuji apples (Malus pumila Mill.) were purchased from a local fruit market (Tai’an, China). Commercial wine yeast Lalvin CY 3079 was purchased from Shanghai Jatou Industry and Commerce Co., Ltd. (Shanghai, China). Malic acid (Shanghai Wankang Biotechnology Co., Ltd, China) was ordered at a local food additive store, and bentonite was kindly provided by Weifang Kaize Oenology Material Co., Ltd. (Weifang, China). Methanol standard (chromatographic grade) was purchased from Shandong Yuwang Pharmaceutical Co., Ltd. (Dezhou, China), and tert-amyl alcohol from China National Research Institute of Food and Fermentation Industries (Beijing, China) was used as an internal standard. PME ELISA kit was ordered at Shanghai Hengyuan Biological Technology Co., Ltd (Shanghai, China). All other reagents were of at least analytical grade.
