Sunday, May 4, 2008
2-59

Cellulase production by solid-state fermentation in different bioreactors scales

Iara R. Pinheiro, João G.D. Klemz, and Beatriz V. Kilikian. Chemical Engineering Department, Universidade de São Paulo, Av. Prof. Luciano Gualberto, trav.3, n.380, São Paulo, SP 05508-900 Brasil, São Paulo, Brazil

Solid-state fermentation (SSF) is an alternative to submerged cultures because it is possible to achieve high specific productivity and to apply low-cost substrates such as corncobs, wheat bran and sugarcane bagasse. Scaling up SSF processes raises several engineering problems due to the build-up of gradients of temperature, pH, oxygen and moisture. The objetive of this study was to compare cellulase production under two types of bioreactors and two scales: 0.3 L packed bed columns and a 30 L internally agitated horizontal drum bioreactor. Fermentations were performed by Trichoderma reesei RUT C30, using solely wheat bran and a mix of wheat bran (20%) and sugarcane bagasse (80%) as substrate. Culture conditions were 60% moisture (wet basis), inoculation with 107 spores.gdm-1, 30°C temperature. Aeration rate was 100 mL.min-1 in packed-bed columns and 20L.min-1 in the bioreactor, employing an agitation pattern of 4 turns every 6 hours. Enzyme extraction was performed with 20 mL of a 1:1 mixture of water and citrate buffer (pH 4.8) per g of fermented medium (wet basis), and FPase and CMCase activities were estimated.

The best activity values were observed for wheat bran fermentations at the third day, at 3.8 U/gdm FPA and 9.54 U/gms CMC. The activities obtained in the reactor were smaller, mainly due to the temperature gradients observed with both substrates, impairing the microbial growth and cellulase production. Considering this condition, further studies including different agitation patterns are to be conducted, to obtain sucessful scale-up criteria.


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