Kinetic analysis of the uptake of glucose and corn oil used as carbon sources in batch cultures of Gibberella fujikuroi

This study determined the specific uptake rate of glucose and corn oil substrates used as carbon sources in batch cultures of Gibberella fujikuroi. We tested three biological models of growth rate: Monod, logistic and lag-exponential. With respect to the substrate consumption rate, we tested two models: constant cell yield ( CCY) and law of mass action ( LMA). The experimental data obtained from the culture with glucose as substrate correlated satisfactorily with the logistic/LMA model, indicating that the cell yield was variable. In the case of corn oil as carbon source, considering total residual lipids as substrate in the culture broth, the model with the best correlation was the lag-exp/CCY model. The quantification by GC of the three main fatty acids ( linoleic, oleic and palmitic) in the culture medium showed a cumulative behavior, with a maximum concentration of each acid at 36 h. We established a more explicit mechanism of the consumption of corn oil, consisting of two stages: generation of fatty acids by hydrolysis and consumption by cellular uptake. The kinetic of hydrolysable lipids was of first order. We found that the hydrolysis rate of corn oil is not a limiting factor for the uptake of fatty acids by the microorganism. We also established, based on the analysis of the identical mathematical structure of consumption kinetics, that the uptake of fatty acids is faster than the uptake of glucose.