2.5 Metabolite analysis
After centrifuging the sample, the supernatant was obtained through a 0.22 μM filter and then analyzed. All metabolites were analyzed by HPLC equipment (Agilent, Waldbronn, Germany) with the HPX-87H column (Bio-Rad, CA, USA). The different detectors (refractive index and ultraviolet) were used at the same time and the ultraviolet wavelength was controlled at 210 nm. The 30 mM H2SO4 at 0.3 mL/min at 42 °C was used in the detect process(Babu et al., 2015; Zhao, Li, & Deng, 2018).