Thermostability of crude endoglucanase from Aspergillus fumigatus grown under solid state fermentation (SSF) and submerged fermentation (SmF)

Aspergillus fumigatus produced more protein (114 μg/ml vs 51 μg/ml) and a higher specific activity of the endoglucanase (9158 vs 6294) in the culture filtrates from solid state fermentation (SSF) than that from submerged fermentation (SmF) when grown on wheat straw. The activation energy (Ea) of substrate hydrolysis was less (33 kJ mol−1) for the endoglucanase produced under the SSF (SSF-EG) than the enzyme produced under the SmF (SmF-EG), which was 51 kJ mol−1. The SSF-EG was more thermostable as compared to the SmF-EG, evidenced by the larger enthalpy of activation of denaturation, ΔHD*, 152 kJ mol−1 vs 112 kJ mol−1 at 50 °C (similar results at higher temperatures). It was further evidenced by a steeper decline in the half lives (T1/2) of the SmF-EG than the SSF-EG. The free energy changes of activation of denaturation of the enzymes, ΔGD*, were 107 kJ mol−1 and 106 kJ mol−1 for the SSF-EG and the SmF-EG, respectively, at 50 °C (similar results at higher temperatures). The entropies of activation of denaturation, ΔSD*, were positive for both of the enzymes. The melting temperature (Tm) of the enzyme was 5 °C more for the SSF-EG than the SmF-EG.