Ethanol and value-added byproducts from rice straw by dimorphic fungus Mucor hiemalis

Different morphologies of Mucor hiemalis were induced and used for the production of ethanol and biomass from rice straw through a separate hydrolysis and fermentation process. The yield of enzymatic hydrolysis was improved from 40.4% for the untreated straw to 80-93% by employing sodium hydroxide and concentrated phosphoric acid pretreatments with or without ultrasonication. The best hydrolysis performance was achieved after pretreatment by sodium hydroxide assisted with ultrasonication. The ethanol yields from the hydrolysates were 0.39-0.44 g/g depending on the pretreatment method and the fungus morphology. The yeast-like form of the fungus showed faster glucose assimilation and slightly higher ethanol yield compared to the other morphologies. The biomass yield of mostly yeast-like cells was more than the other morphologies (0.202-0.282 g/g glucose). Moreover, the biomass of the yeast-like cells had more protein content (46.7-52.4 %) compared to filamentous cells (37.7-46.3 %). The cell wall, alkali-insoluble material (AIM) of the biomass, represented 16.3-20.1% of the biomass. On average, total chitin-chitosan content of AIM of the biomass of purely filamentous, mostly filamentous, mostly yeast-like, and purely yeast-like forms of the fungus was 0.460, 0.373, 0.330, and 0.336 g/g AIM of the biomass, respectively.