Abstract
The effect of the partial pressure of O 2 and CO 2 on the acid protease production in solid state fermentation by Aspergillus niger on wheat bran was studied. A fermentation system was used, which allowed on-line reactor measurements and continuous data acquisition of pH, temperature, gas flow, pressure drop and CO 2 production. Six paired combinations of CO 2 and O 2 concentrations were studied. The results showed a direct relationship between pressure drop, production of CO 2 and temperature increase. The pH evolution patterns were similar in all cases but different if the measurements were made on-line or on a liquid homogenate of the fermented substrate. Acid protease production was increased when the gas had 4% CO 2, (vol/vol), and it reached its highest level, a 43% increase over air, with a mixture of 4% CO 2 and 21% O 2. The protease production was strongly related to the mold metabolic activity as represented by the total CO 2 evolved.
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