Abstract

Effects of culture broth pH values on cells growth and lipid production were investigated in heterotrophic cultivation of Chlorella protothecoides. Based on the phenomenon that lower pH value favors cells growth but retards lipid synthesis and vice versa for higher pH value, a novel pH-shift strategy, optimized via simulating Gauss function, was developed. By controlling pH at 5.0 for first 93 h and switching to 6.5 afterwards, final lipid yield and productivity reached 3.75 g/L and 20.8 mg/L/h, increased by 24.2 and 38.7%, respectively as compared to constant pH 6.0 operations. Moreover, by feeding glucose and aqueous ammonia replacing sulphuric acid (H₂SO4) and NaOH solutions to control pH, maximal lipid yield of 3.96 g/l was achieved, suggesting application of the novel pH-shift strategy for lipid overproduction as being feasible.

Key words: Heterotrophic cultivation, lipid, ph-shift strategy, glucose and Chlorella protothecoides.