Effect Of Pleutrotus Ostreatus Combined With Ammoniation Pretreatment On Enzymatic Sugar Yield From Corn Stover

Biofuels from the conversion of lignocellulosic biomass can reduce the global reliance on fossil fuels and greenhouse gas emissions.Lignocellulosic biomass is abundant,renewable and inexpensive,but pretreatment is considered an essential step due to its complex heterogeneity and recalcitrance.Biological pretreatment,although highly promising due to its green and energy-efficient properties,also presents shortcomings such as being time-consuming and inefficient.Biological combined with chemical pretreatment can improve treatment efficiency and save reagents.However,the most common biological combined with alkali pretreatment also presents problems due to the use of intense alkali which is prone to inhibitors and requires additional washing steps.Therefore,in this paper,one of the most cultivated and consumed edible mushrooms in the world,and which selectively degrades lignin,the Pleutrotus ostreatus was selected for biological pretreatment and chemical pretreatment with a mildly reactive ammonia reagent.In this paper,we investigated the effect of pretreatment with Pleutrotus ostreatus and high solids ammoniation,and its combined pretreatment on the enzymatic sugar yield from corn stover,using corn stover as raw material for the production of ethanol.The main studies were as follows:(1)The effects of inoculum level,moisture content and fermentation time on the enzymatic sugar yield from corn stover based on reducing sugar yield and weight loss as the main indicators,and the effects of pretreatment of Pleutrotus ostreatus on the structure of corn stover were explored by scanning electron microscopy and Fourier Transform Infrared Spectrometer.The results showed that optimum conditions for the pretreatment of Pleutrotus ostreatus were found to be 10% inoculum,80% moisture content and 28 d fermentation time,at which point the reducing sugar yield was 214.50 mg/g,an increase of 4.14% compared to the raw material.After pretreatment with Pleutrotus ostreatus,the surface of the corn stover showed obvious pores,and the structure of the lignin and cellulose was changed.(2)The effects of the ammoniator species,concentration,solid content and ammoniation time on the enzymatic sugar yield of corn stover were studied,and orthogonal optimization experiments were carried out to determine the optimal ammoniation pretreatment conditions based on single-factor experiments.The optimum conditions were found to be ammoniation with ammonium carbonate at 20% concentration and 50% solid content for 11 d,at which point the reducing sugar yield was 312.67 mg/g,an increase of 51.80% compared to the raw material extraction.After pretreatment of corn stover with ammonium carbonate,the structure of lignin and cellulose changed,the surface structure became rough and loose,and the fibre bundles were exposed,which was more favourable for cellulase action.(3)The effect of combined ammoniated pretreatment of Pleutrotus ostreatus and pretreatment sequence on the enzymatic sugar yield of corn stover was investigated,using reducing sugar yield as the main indicator.The effect of different pretreatment methods on the sugar yield of corn stover was also studied by composition determination and structural characterization.Ammoniation pretreatment of corn stover followed by solid state fermentation reduced the laccase activity secreted by Pleutrotus ostreatus and increased the cellulase enzyme activity,decreasing reducing sugar yield.Solid state fermentation of Pleutrotus ostreatus followed by ammoniation pretreatment significantly improved reducing sugar yield up to 374.55 mg/g,which was 81.85% higher compared to the raw material.When Pleutrotus ostreatus was pretreated for 21 d followed by 10% ammonium carbonate for 11 d,the reducing sugar yield was 311.09 mg/g,saving 50% of the reagent compared to the 20%ammonium carbonate pretreatment alone.Scanning electron micrographs showed significant structural changes in the corn stover after pretreatment by the different methods,with the combined pretreatment resulting in the greatest damage to the corn stover surface,with more obvious pores,furrows and cracks.The Fourier Transform Infrared Spectrometer results showed that the structures of both lignin and cellulose of the corn stover have been destroyed after pretreatment by different methods.Diffraction of x-rays results showed that the crystallinity of the corn stover decreased after pretreatment by the different methods,with Pleutrotus ostreatus fermentation for 21 d + 10% ammonium carbonate pretreatment showing the most significant decrease in crystallinity.