The yeast fermentation media consisted of filter sterilised hydrolysate (0.22 lm, nylon filter, Millipore, MA, USA) containing 2 g/L KH2PO4, 5 g/L yeast extract, 10 g/L peptone and 1 g/L MgSO4 and were inoculation directly with dried yeast at 5 g/L to initiate fermentation.