where St(g L−1) is the total substrate required to produce Xt(g L−1),which is the total biomass produced at culture time t; YX/S(g g−1)is the yield of biomass from the total substrates, which was setat 0.6 for all substrate ratios and estimated based on the biomass yields from fatty acid and glucose described in previous studies(Sun et al., 2006, 2007a). X0(g L−1) is the initial biomass concentration before feeding starts which was estimated at 0.65 g L−1; and is the desired specific growth rate (0.15 h−1).