Effect of Multiple Inhibitions in Corncob Hydrolysate on the Lipid Production by Rhodotorula glutinis

Lignocellulosic biomass degradation byproducts generated in the pretreatment process have various negative impacts on microbes. This work investigated the effects of multiple inhibitors, such as acetic acid, furfural, and 5-hydroxymethylfurfural (HMF), on cell growth and lipid production by Rhodotorula glutinis. Single-factor experiments were performed to study the individual inhibitory actions. Among the three inhibitors, furfural is the most toxic for the cell growth, followed by HMF and then acetic acid. At 0.8 g/L furfural, the biomass and lipid concentrations decreased by 18.1 and 27.0% compared to the control. R. glutinis has a strong tolerance to acetic acid. Biomass and lipid production could even be stimulated when the acetic acid concentration was lower than 10 g/L. The effect of multiple inhibitions on the cell growth and lipid production was further studied using response surface methodology (RSM). The interaction of furfural and acetic acid was significant (p < 0.0001), but for the case of acetic acid and HMF or furfural and HMF, it was non-significant. With a furfural concentration above 0.4 g/L, the existence of acetic acid resulted in a dramatic decline of the biomass and lipid yields. Two models were proposed on the basis of RSM for predicting the biomass and lipid syntheses when multiple inhibitors existed. The verification results demonstrated that the models fit the experimental data well and the relative deviation was less than 6%. Although the interaction of acetic acid and furfural was significant, R. glutinis showed high tolerance to those inhibitors. The models set up in this work provided a tool for further control and optimization when using undetoxified lignocellulosic hydrolysate for lipid production. This work was helpful for a deeper understanding on the lipid metabolism of R. glutinis.