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

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 tarmases, 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 (mum), 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, mu(M) Y-P/X X-M, corrected by a function of v = k/Y-P/X mu(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 mu(M)X(M). Studies with pectinases resulted in higher values of YP/XXM. 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. (C) 2002 Elsevier Science B.V. All rights reserved.