Production of amylases from rice by solid-state fermentation in a gas-solid spouted-Bed bioreactor

A gas-solid spouted-bed bioreactor was developed to produce amylases from rice in solid-state fermentation by Aspergillus oryzae. The spouted-bed bioreactor was developed to overcome many of the problems inherent to large-scale solid-state fermentation, including mass- and heat-transfer limitations in the conventional tray reactors and solids-handling difficulties seen in packed-bed bioreactors. The solid-state fermentation results from the tray-type reactor with surface aeration were poor because of mass- and heat-transfer problems. A packed-bed bioreactor with continuous aeration through the rice bed produced high protein and enzymes, but the fermented rice was difficult to remove and process due to the formation of large chunks of rice aggregates knitted together with fungal mycelia. Also, the fermentation was not uniform in the packed bed. The spouted-bed bioreactor with intermittent spouting with air achieved high production levels in both total protein and enzymes (alpha-amylase, beta-amylase, and glucoamylase) that were comparable to those found in the packed-bed bioreactor, but without the nonuniformity and solids-handling problems. However, continual spouting was found to be detrimental to this solid-state fermentation, possibly because of shear or impact damage to fungal mycelia during spouting. Increasing spouting frequency from 4-h intervals to 1-h intervals decreased protein and enzyme production. Other operating conditions critical to the fermentation include proper humidification to prevent drying of the substrate and control of reactor wall temperature to prevent excessive condensation, which would interfere with proper spouting.