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Inoculum production for Solid-state Fermentation in pilot scale
Suzuki, R. S.; Barga, M.C.; Mitchell, D.A.; Sassaki, G.L.
Departamento de Bioquímica e Biologia Molecular, UFPR
Solid-state
fermentation is a promising technique for the production of
biotechnological products, using solid agro-industrial residues as
substrates. However, there are only a few processes that uses this
technique in industrial scale, due to difficulties in process scale-up.
The present study aimed to minimize one of these problems, the
production of adequate volumes of inoculum, using the microorganism Rhizopus oryzae as a model organism. At laboratory scale, a concentration of 106 spores
per gram of substrate is normally used. At large scale it is very
difficult to obtain an adequate inoculum volume with this spore
concentration by traditional cultivation in BDA medium (note that 100 g of BDA medium provides 100 ml of spore solution with a concentration of 6.102x106 spores.ml-1).
The effect of the water content of the solid medium on the production
of spores was studied. The assays were done in a substrate containing 50 g
of dry rice and water. After autoclaving and cooling, the substrate was
inoculated with 5 ml of the spore solution. In different treatments the
water contents (dry basis) after inoculation were 60%, 70% and 80%.
Cultures were cultivated for 7 days at 34°C. The spores were harvested with sterile distilled water, resulting in 300 ml of spore solution for every 50 g of dry substrate. The spore concentrations were 1.11x107 spores.ml-1, 9.42x106 spores.ml-1 and 5.10x106 spores.ml-1,
for the cultures with 60%, 70% and 80% initial water content,
respectively. An analysis of the results obtained with the best initial
water content (60%, dry basis), in comparison with the BDA-based spore
production method, shows that this treatment gives a 3.75-fold greater
volume of inoculum solution for the same mass of substrate. Further the
spore concentration in this inoculum solution is two-fold greater. The
overall spore yield was therefore improved 7.5-fold. This technique of
spore production can be utilized in pilot-scale solid-state
fermentation processes for the production of biotechnological products. Support: CNPq and CT-Agro
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