Effect of Mixing on the Solid-State Fermentation of Coffee Pulp with Aspergillus tamarii

Solid-state fermentation of coffee pulp with Aspergillus tamarii V12307 was carried out in laboratory scale reactors (bottle and column) to evaluate the effect of four different mixing frequencies (2.0, 2.7, 4.0 and 8.0 day^–1) on fungal growth, indirectly determined by carbon dioxide formation and the production of spores and pectin methylesterase. Coffee pulp was used as the sole source of nutrients. An increase in the fraction of bonded particles was observed in the bottle reactors after 12 h of cultivation when no mixing was applied. The use of any mixing frequency reduced the fraction of bonded particles. However, there was no significant difference in pectin methylesterase production between the mixing frequencies at the end of the fermentation. Similarly, there were no significant differences in CO2 production, oxygen uptake or sporulation, demonstrating that the mycelium was not damaged by intermittent mixing. This strategy of mixing could be used in large scale reactors in order to reduce heat and mass limitations