2.5. Analytical methods
Glucose concentration was analyzed by an enzymatic bio-analyzer (SBA-40C, Shandong Academy of Sciences, China). Rapeseed oil concentration in the broth was quickly determined by the low-field nuclear magnetic method. [19] For biomass determination, three parallel broth samples were washed twice with alcohol and dried at 80℃ for 24 h to measure dry cell weight (DCW). The concentrations and structures of SLs were determined by HPLC and HPLC-MS, respectively. [7]