2.3.1 Dry cell weight and cell density determination
DCW was calculated as described previously (Wen, Zhang, & Tan, 2005).
2.3.2 Glucose and β-carotene analysis
The glucose concentration of fermentation broth was measured by an SBA-40C bio-analyzer (Shandong Academy of Sciences; Jinan, China).
The β-carotene was extracted as described previously (Gao et al., 2017) and measured by HPLC (Agilent Technologies 1260 Infinity Series system, USA) using a C18 column at UV 450nm. Methanol, acetonitrile, and isopropanol (30:50:20) were used in the mobile phase at a flow rate of 1.0 mL/min at 30 ℃.