Comprehensive utilization of Aspergillus niger waste mycelium based on physically induced autolysis: Preparation of chitosan and alternative nitrogen source

Abstract

In industrial fermentation of citric acid, vast quantities of mycelium from Aspergillus niger (MAN) are produced, with an annual output of 20 million tons in China alone. The disposal of waste MAN poses a significant challenge and signifies a missed opportunity for resource recovery. In this study, physically induced autolysis (PIA) was employed to utilize the MAN proteins and chitosan. The results indicated abundant soluble proteins and sugars were released into the supernatant, while the cell fragments can be used to prepare chitosan. Under optimized autolytic conditions, the rate of total protein utilization of MAN was 78.7 %, and the rate of reserved chitin in the cell fragment was 93.8 %, outperforming other techniques. These findings were consistently reproducible in larger-scale experiments. Chitosan was prepared from cell fragments that eliminated the need for acid treatment and reduced alkali utilization by 50–67 %, thanks to PIA's effective removal of proteins from cell fragments. The rate of total sugar utilization, including both the content of the soluble sugars from autolysate and prepared chitosan, was 75.42 % of the total sugar of MAN. Additionally, the autolysate was proved to be an alternative nitrogen source in the fermentation media for microbial production of 2, 3-butanediol and citric acid, yielding concentrations comparable or superior to traditional sources. Thus, our findings not only achieved high component utilization rates but also facilitated environmentally friendly chitosan preparation, indicating the potential for innovative approaches to convert waste mycelium into valuable resources and advance the industry towards more efficient practices.