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, indicated steep gradients in temp. and enzyme [amyloglucosidase (glucan 1,4-alpha-glucosidase)] levels at different depths in deep bed rectangular fermenters with different loads. An increase of about 2.5C 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 resulted in a doubled fermentation time to attain enzyme levels comparable with those in a fermenter with a load of 17.8 kg m-2. Temp. variations were about 10-18C for a bed depth of 80 mm and the max. enzyme levels were 23.4% lower with a load of 49.7 kg m-2 compared with those for a load of 17.8 kg m-2. Metabolic heat and enzyme biosynthesis functions were significantly affected by an increase in bed depth. Max. temp. variations recorded in the fermenter with a load of 126.1 kg m-2 were 19.5C at 12 h and 21.2C at 60 h for 80 and 160 mm bed depths, respectively. Consequently, max. 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. Results indicate that temp. gradients play a key role in the biosynthesis of enzymes in a solid state fermentation system involving deep beds.