2.2. Culture media and microorganism culture
The composition of culture media is shown in Table 1. The activated S. cerevisiae (Nanyang) was inoculated into flesh slant culture medium in a test tube and cultivated in a thermotank at 30 °C for 1–3 d until the white lawn appeared on the slant culture and distributed evenly. Precultures were incubated for 20–24 h at 30±0.5 °C with orbital shaking at 150 rpm in a 25 ml-test tube containing a loopful of yeast cells in 10 ml liquid culture medium. When the yeast cells were up to 108 cells ml−1 observed by microscope, the yeast cells in liquid culture medium were mature; Fermentation culture was carried in a 500 ml flask with a working volume of 200–250 ml. The flask was inoculated with 20–25 ml mature yeast cells of liquid culture medium and incubated at 30 °C and 150 rpm for about 48 h. When the yeast cells were up to 108 cells ml−1, the yeast cells in fermentation culture medium were mature, and could be used for the yeast cells immobilization.