Enhanced ethanol and chitosan production from wheat straw by Mucor indicus with minimal nutrient consumption

Abstract

Recently, Mucor indicus was introduced as a promising ethanol producing microorganism for fermentation of lignocellulosic hydrolysates, showing a number of advantages over Saccharomyces cerevisiae. However, high nutrient requirement is the main drawback of the fungus in efficient ethanol production from lignocelluloses. In this study, application of fungal extract as a potential nutrient source replacing all required nutrients in fermentation of wheat straw by M. indicus was investigated. Wheat straw was pretreated with N-methylmorpholine-N-oxide (NMMO) at 120°C for 1–5h prior to enzymatic hydrolysis. Hydrolysis yield was improved at least by 6-fold for 3h pretreated straw compared with that of untreated one. A fungal extract was produced by autolysis of M. indicus biomass, an unavoidable byproduct of fermentation. Maximum free amino nitrogen (2.04g/L), phosphorus (1.50g/L), and total nitrogen (4.47g/L) as well as potassium, magnesium, and calcium in the fungal extract were obtained by autolysis of the biomass at 50°C and pH 5.0. The fungal extract as a nutrient-rich supplement substituted yeast extract and all other required minerals in fermentation and enhanced the ethanol yield up to 92.1% of the theoretical yield. Besides, appreciate amounts of chitosan were produced as another valuable product of the autolysis.