.2 Yeasts
The Tibetan yeasts for screening were provided by the Key Laboratory of Dairy Biotechnology and Engineering, Ministry of Education (Inner Mongolia Autonomous Region, China). They were isolated from yak yoghourt, identified by large-subunit (26S) ribo- somal DNA (rDNA) D1/D2 domain sequence analysis,ored in ampoule tubes in lyophilized form at −80 °C, and activated on nutrient yeast dextrose agar (NYDA: 8 g nutrient broth, 5 g yeast extract, 10 g glucose, and 20 g agar in 1 L of distilled water) for two generations at 28 °C in the dark. Before the experiments, yeasts were inoculated by immersing a loop in 50 ml NYD broth (NYDA without agar) and incubated at 28 °C on a rotary shaker at 200 r/min for 24 h. To remove the medium, the cells were centrifuged at 3500g for 10 min and rinsed twice in sterile distilled water. Then, the pellets were re-suspended in sterile distilled water and adjusted to the required concentrations by counting cells with a hemocytometer.