Screening of agro-industrial waste and physical factors for the optimum production of pullulanase in solid-state fermentation from endophytic Aspergillus sp.

Abstract

Abstract The selection of a suitable agricultural residue, its availability and the cost are critical factors to be considered while selecting a raw material in solid-state fermentation (SSF). In the case of SSF parameters like temperature, moisture content and spore concentration also play a significant role in enzyme production. In this study, endophytic fungi were isolated and screened for their pullulanase activity. The most promising isolate identified as Aspergillus sp. was evaluated for the pullulanase production using agricultural residual substrates like wheat bran, rice bran, sugarcane bagasse, orange peel, mosambi peel, and banana peel. Among all the substrates tested by the classical approach, the wheat bran was found to be the most effective substrate. The highest yield was 65.33 ± 2.08U/gds, while in case of rice bran the maximum yield was 44.66 ± 1.527U/gds. The comparatively lower yield was obtained in sugarcane bagasse, orange peel, mosambi peel, and banana peel. Maximum Pullulanase activity (67.00 ± 01.00 U/gds) was reached on 3rd day; thereafter the enzyme activity declined. Experiments conducted at the optimum physical conditions (temperature 28.62 °C; moisture 69.92%; inoculum size 6.42 log) demonstrated that the pullulanase yield (396.2 ± 1.33U/gds) was closer to the predicted value (394.5U/gds). There was an improvement of yield by 6.064 fold relative to that obtained from un-optimized physical parameters. The good correlation between predicted and experimental values after optimization justified the validity of the response model and the existence of an optimum point. This is the first report of pullulanase production from Aspergillus species in solid-state fermentation.