Screening Of Yeast In Grapes And Preliminary Study On The Process Of Degrading Corn Straw To Produce Ethanol By Two-Step

Corn stalk is a kind of resource-rich lignocellulose,which is mainly composed of lignin,cellulose and hemicellulose,but has not been fully utilized,which has resulted in waste of resources and environmental pollution.Increasing demand for energy and fossil fuels has led to research on biomass lignocellulosic fuel production,Biofuels based on sustainable non-edible lignocellulosic biomass conversion are one of the main cornerstones of replacing fossil fuels with renewable resources worldwide.In this paper,corn straw was used as the raw material for fermentation,and the research was carried out from three aspects:screening and identification of yeasts,optimization of fermentation conditions,and optimization of the amount of nutrients added to the medium.(1)Nine strains of yeast were screened from grapes,and three strains that were in line with the characteristics of ethanol production were obtained by screening WL medium and TTC medium;Corn straw as raw material,the fermentation broth containing polysaccharide was obtained by preliminary saccharification and fermentation of Streptomyces for 6 days,and the three yeasts were inoculated into the polysaccharide fermentation broth for secondary fermentation,and the highest concentration of ethanol was screened out,No.Y1.The Y1 strain was sequenced and identified by 26S r DNA gene,and the Y1 strain was identified as Saccharomyces cerevisiae.(2)Through single-factor influence experiments,the suitable range of straw fermentation conditions was initially determined:p H value was 4.5-6.0,fermentation temperature was 31?-37?,inoculation amount was 6%-12%,and rotation speed was 120r/min-200r/min.Orthogonal experiments show that the order of influence factors is:p H value,inoculation amount,rotation speed,fermentation temperature.p H5.0,fermentation temperature 34°C,inoculation amount 10%,and rotation speed120r/min are the optimum fermentation conditions.Under this condition,the ethanol concentration reached 2.473g/L.The results of HPLC method showed that Saccharomyces cerevisiae had very high utilization efficiency of six carbon sugars and low utilization efficiency of five carbon sugars.(3)According to the comparison of experimental results,the amount of peptone was one of the factors.Single factor experiments were performed on peptone,MgSO₄,and KH₂PO₄.The results showed that the appropriate amount of peptone was 7.5 g/L-15 g/L,the amount of MgSO₄ was 0.5 g/L-1.25 g/L,and the amount of KH₂PO₄1 g/L-2.5 g/L.Orthogonal experiments showed that the major and minor order of the impact factors were peptone,KH₂PO₄,and MgSO₄.The optimal combination was:peptone 12.5 g/L,MgSO₄ 0.75 g/L,KH₂PO₄ 0.5 g/L.The ethanol concentration under this combination can reach 2.704g/L.