The inhibition effect of phenol on the production of Aspergillus niger inulinase and its modeling

Abstract

The main objectives of this study were to investigate the effect of phenol on the production of Aspergillus niger A42 (ATCC 204447) inulinase and to model the best fermentation in the medium with inhibitor. When the phenol concentrations added into the fermentation medium increased from 0 to 5 g/L, the inulinase and invertase-type activities and the maximum inulinase and invertase-type production rates were reduced from 203.0 to 12.6 U/ml and from 156.9 to 3.1 U/ml, and from 32.6 to 2.9 U–1 · ml–1 · day–1 and from 32.6 to 1.1 U–1 · ml–1 · day–1. Additionally, the modified Gompertz, modified logistic, and Baranyi and Huang models successfully predicted the experimental data of inulinase production, invertase-type production, and substrate consumption, respectively. Consequently, renewable resources can be used in inulinase productions without detoxification when the hydrolysate contains low concentrations of phenol. Furthermore, the models can serve as universal equations in modeling the enzyme fermentation in shake flask fermentation. Practical applications Inulinase is used in various fields such as the production of prebiotic products fructooligosaccharides (FOS) and inulooligosaccharides (IOS), bioethanol, and fructose syrup. In addition to pure carbon sources, industrial wastes such as molasses or renewable resources are used as carbon sources. To use renewable resources, various pretreatments are applied before the upstream process. During pretreatment, various inhibitors such as phenols that are mostly formed by the degradation of lignin adversely affected fermentation. Phenolic compounds are removed from the fermentation medium by detoxification processes. The detoxification process is a very costly and time-consuming, although it is very important for the efficiency of the fermentation. For this, the determination of the tolerance ranges of the microorganism to the phenol compounds is essential. Knowing the tolerance of Aspergillus niger used in this study to the phenol compound will benefit the industry in the use of dilute, direct or detoxifying hydrolysates.