Temperature variations and amyloglucosidase levels at different bed depths in a solid state fermentation system

Studies on moist wheat bran medium, inoculated with Aspergillus niger CFTRI 1105, indicate steep gradients in the temperature and enzyme levels at different depths in deep bed rectangular fermenters with different loads. An increase of about 2.5 °C over a bed depth of 40 mm in a fermenter with a load of 49.7 kg m⁻² was due to metabolic heat generation in the initial fermentation period. This was found to result in a doubled fermentation time to attain enzyme levels which were comparable, although still lower by 4.6%, with those in a fermenter with a load of 17.8 kg m⁻². The temperature variations were about 10–18 °C for a bed depth of 80 mm and the highest enzyme levels were lower by 23.4%, even after 48 h, with a load of 49.7 kg m⁻² compared with those for a load of 17.8 kg m⁻² . The metabolic heat and enzyme biosynthesis functions were found to be significantly affected by an increase in bed depth. The maximum temperature variations recorded in the fermenter with a load of 126.1 kg m⁻² were 19.5 °C at 12 h and 21.2 °C at 60 h for 80 and 160 mm bed depths respectively. Consequently, the maximum enzyme levels were lower by 81%–86% and required a 2.5-fold increase in fermentation time compared with a fermenter with a load of 17.8 kg m⁻².

The results indicate that the temperature gradients play a key role in the biosynthesis of the enzyme in a solid state fermentation system involving deep beds.