Investigation of the inhibitory effects of furfural and hydroxymethylfurfural on the production of Aspergillus niger inulinase and modeling of the process

Due to the limited natural resources, the tendency toward using agro-industrial wastes as the main substrate in the biotechnological productions has increased. In order to obtain biologically available compounds out of these wastes, various extraction processes need to be applied. However, during these processes, some other inhibitory compounds such as furfural and hydroxymethylfurfural (HMF) also occur. Therefore, evaluation of these inhibitor effects on the biological systems before using these wastes as substrate is crucial for the overall success of the process. This study was undertaken to investigate the effect of various concentrations of furfural and HMF on the Aspergillus niger A42 (ATCC 204,447) inulinase activity, invertase activity, biomass production, and sugar consumption in sucrose-based medium and to model the production outcomes. The results showed that furfural had higher inhibitory effect on the process than HMF at the same concentrations. However, fungi were able to tolerate up to 3 g/1 of HMF or 0.5 g/l of furfural in the production medium with minor changes in the yield. The highest inulinase activities were measured as 268.737 and 197.350 U/ml in the presence of 1 g/l of HMF and 0.1 g/1 of furfural, respectively. In these conditions, inulinase productions were successfully represented by Baranyi and Weibull models. This study clearly showed that inulinase production with Aspergillus niger A42 can be successfully performed in the presence of a certain amount of furfural and HMF, which indicates the strength of potential usage of lignocellulosic materials as production substrate.