Advantages of fungal enzyme production in solid state over liquid fermentation systems

Abstract

The present paper attempts to explain why enzyme production in solid-state fermentation (SSF) is higher than in submerged fermentation (SmF). Recent work done in our laboratory [Biotechnol. Lett. 22 (2000) 1255; J. Ind. Microbiol. Biotechnol. 26 (5) (2001) 271; J. Ind. Microbiol. Biotechnol. 26 (5) (2001) 296] related to the production of invertase, pectinases and tannases, by Aspergillus niger grown by SSF and SmF is reviewed. To do such a comparative study, logistic and Luedeking–Piret equations are used in order to estimate the values of the following coefficients: maximal specific growth rate ( μ M), maximal biomass level ( X M), enzyme/biomass yield ( Y P / X ) and secondary rate of production, or breakdown ( k). It is shown that enzyme productivity is proportional to group, μ M Y P/ X X M, corrected by a function of ν= k/ Y P/ X μ M. In all three cases of enzyme production studied, productivity using a SSF system was higher than in SmF. Studies with invertase resulted in higher values of μ M X M. Studies with pectinases resulted in higher values of Y P/ X X M. Studies with tannases resulted in higher Y P / X and less negative values of k. Finally, a reaction–diffusion model is presented to try to explain such differences based on micrographic measurements of mycelial aggregates for each kind of fermentation system.