The Study On Effects Of Bioactive Compounds From Rice Straw On Ethanol Fermentation By Yeast

Lignocellulose is widely used in the production of biofuel ethanol.Rice straw is a kind of the most abundant renewable carbon source with low cost.Bioethanol has a significant impact on the environmental pollutions caused by fossil fuel combustion,the high cost of renewable energy and the lack of raw materials.On the other hand,the bioconversion of rice straw into ethanol can alleviate the energy crisis and solve problems related to waste treatment.Bioethanol provides new ideas and possibilities for efficient utilization and biotransformation of lignocellulose biomass.The traditional pretreatment methods of lignocellulose have many limitations.The release rate of monosaccharide is not high and environmentally unfriendly.At the same time,it will produce many inhibitors to inhibit the production of ethanol,which will lead to bioethanol is not competitive in the energy field.The key of the whole bioethanol process is how to improve the conversion efficiency of ethanol and reduce the cost of ethanol production.In order to solve these problems,the inhibitory effect of phenolic acids released from rice straw during ball milling and enzymatic hydrolysis on ethanol fermentation and the mechanism of the inhibitory effects were studied in this paper.In order to reduce the production cost of bioethanol and increase the competitiveness of bioethanol in the field of energy.Major findings are as follows:A large amount of phenolic acids is released during saccharification of rice straw and process of ball milling.The type of phenolic acids was the major factor affecting ethanol fermentation by Pichia stipitis.Free phenolic acids exhibited much higher inhibitory activity than conjugated phenolic acids.Different cellulases produced different ratios of free phenolic acids to soluble conjugated phenolic acids,resulting in different fermentation efficiencies.The results of the correlation analysis revealed the inhibitory effect of p-CA(Spearman correlation =-0.374,P = 0.036),FA(Spearman correlation =-0.449,P = 0.014)on ethanol production,indicating that the free phenolic acids would be the major inhibitors formed during saccharification.The flow cytometry results indicated that the damage to cell membranes was the primary mechanism of inhibition of ethanol fermentation by phenolic acids.The removal of free phenolic acids increased ethanol productivity 1.8-fold and markedly improved the production of value-added products,and this process may constitute a new strategy for the production of low-cost ethanol.In the process of rice straw hydrolysis,different pretreatments and different cellulases will result in different soluble polysaccharides released in hydrolysates,which will protect yeast during fermentation.In this study,the effect of soluble polysaccharides(SPs)produced during rice straw saccharification on the formation of extracellular matrices(EMs)by the yeast Saccharomyces cerevisiae was investigated.SPs were characterized by high-performance liquid chromatography(HPLC)and fourier transform infrared spectroscopy(FT-IR).SPs reduced the inhibition of alcohol dehydrogenase activity by phenolic acids(PAs)and regulated the intracellular redox state,resulting in higher ethanol production.The results of flow cytometry,confocal laser scanning microscopy,and atomic force microscopy indicated that PAs changed microbial morphology and caused damage in microbial cell membranes.The protective effect of SPs against cell membrane damage could be attributed to the synthesis of polysaccharide-dependent extracellular matrix,which maintained cellular integrity even under phenolic acid stress.These findings provide new strategies to improve pretreatment and saccharification processes.