Improved Production of α-Amylase by Aspergillus terreus in Presence of Oxygen-Vector

Abstract

n-Dodecane has been investigated as an oxygen-vector for improving α-amylase biosynthesis using the strain Aspergillus terreus. In aerobic microbial cultivation, continuous supply of oxygen is required especially due to its low solubility in the growth medium, in particular at high viscosity, but the limitations of oxygen mass transfer in these systems can be overcome by the addition of water-insoluble compounds which possess a strong affinity for oxygen, namely oxygen-vectors. The use of n-dodecane (as an oxygen-vector) in the fermentation medium of A. terreus can significantly improve the bioprocess performance and enhance α-amylase production. Using 5% n-dodecane at 35 °C, an increase of 1.8–2 times in the enzymatic activity was recorded. In the oxygen-vector’s absence, the highest amount of biomass was obtained at 35 °C, while in the presence of 5% vol. n-dodecane, the amount of fungal biomass increased by approximately 70%, with a shift in optimum temperature to 40 °C, generating also an enzymatic activity increase of 2.30 times. Moreover, the oxygen-vector’s addition in the fermentation broth influenced the fungal morphological development in the form of larger pellets with a more compact structure compared to the system without n-dodecane, with a positive effect on the fermentation performance (higher α-amylase activity production).