Fermentation optimization for the production of lipid by Cryptococcus curvatus: Use of response surface methodology

Cryptococcus curvatus is able to grow on crude glycerol derived from the biodiesel production process. Through Box–Behnken design and response surface methodology, the optimal temperature, pH, and glycerol concentration for yeast growth and lipid production on pretreated crude glycerol was identified as 30.2 °C, 6.0, and 19.8 g/l, respectively. Adopting these optimal parameters, the biomass density obtained was 7.11 ± 0.36 g/l with a lipid content of 38.53 ± 1.88%, which matched well with predicted values of 6.98 g/l and 41.31%, respectively. The resulting parameters of the response surface method optimization were used in a fed-batch fermentation where crude glycerol was automatically pumped in responding to exhausted oxygen levels in the fermentor. At the end of 12 days, the biomass concentration was 44.53 g/l and the lipid content was 49.0%. Compared with our previous fed-batch experiment which was conducted under un-optimized condition and manual feeding, the yield of biomass and lipid increased 35.26% and 25.29%, respectively. The optimal parameters and the automatic pumping scheme developed from this study will assist greatly in future industrial scale application of producing microbial oils from crude glycerol.

► The optimal condition for growing Cryptococcus curvatus on crude glycerol was identified.
► Response surface methodology is suitable for optimizing yeast fermentation.
► A fed-batch process adopting the optimum parameters improved lipid yield.
► Crude glycerol can be pumped automatically by controlling oxygen level.