The activity of XTH in strawberry was determined by enzyme-linked immunosorbent assay kit (Hengyuan Biotechnology Co., Ltd, Shanghai, China). Strawberry samples (1 g) was extracted with 4 mL 0.01 mol L 1 pH 7.4 PBS buffer, and then centrifuged at 5000g for 15 min. The supernatant was collected and stored at low temperature. According to the manufacturer’s instructions, the reagent provided by the kit was added to the purified plant XTH antibody microplate in turn, and the absorbance value was determined at 450 nm. The activity of XTH in the sample was calculated by the standard curve, and the result was expressed as U kg 1.
