A 300 cm3 conical flask containing 100 cm3 of 5% YPD medium (1% yeast extract, 2% peptone and 5% dextrose) was sterilized at 121 C for 15 min. A loopful of yeast cells was inoculated into the sterilized medium and was cultivated at 30 C for 16 h with shaking at 2.7 Hz in a rotary shaker (TB-9R-2F; Takasaki Kagaku, Saitama, Japan).