The Preliminary Study On Ethanol Fermentation Using Whole Rice

Ethanol is an important compound and has been widely used in food,chemical,pharmaceutical and other fields.In recent years,ethanol,as a clean energy,has been favored by many countries due to the serious shortage of petroleum and environmental pollution.However,the ethanol productivity in China is very low,with an annual output of only 2.6 million tons.Therefore,China totally needs an additional 10 million tons of ethanol according to the ethanol gasoline popularization policy.Cellulosic ethanol has not yet been industrialized,and less cash crops,such as sugarcane,are not conducive to ethanol production in China.Starch is still the main raw material to expand production.The high-yielding rice in southern China has a large surplus,which means it seems to have new possibilities to produce ethanol using rice.This study aims to explore ways to increase the production of ethanol in industrial production.In this study,the commercial yeast was used to produce ethanol by –whole rice grain fermentation.The enzymatic hydrolysis rate under different conditions were measured and the metabolic changes of yeast under different processes were also studied.Finally,a good process,which has high starch conversion rate,product concentration and productivity,was achieved.This process can realize the production of ethanol with low cost and high efficiency and has practical significance for the industrial production.First,the performance of the high temperature resistant industrial yeast(Saccharomyces cerevisiae)from Angel Yeast Company,was investigated.The yeast has high temperature resistance(37°C),high sugar resistance(100-200 g/L)and certain ethanol resistance.At the same time,the liquefaction enzyme and saccharification enzyme digestion rate used in this study were measured.Addition of liquefying enzyme and glucoamylase to 4.92 and 5.22 U/g substrates.The starch could be hydrolyzed into dextrin and maltose using liquefaction enzyme at 70°C for 1 h.Then the starch could be hydrolyzed completely into glucose with the addition of saccharification enzyme at 50°C for 1.75 h.After the slurry was prepared with warm water at 55°C and maintained at 37°C for 10 h,the hydrolysis rate of starch was up to 66.4%.Secondly,the performance of ethanol production by three fermentation processes including step saccharification(SHF),synchronous saccharification(SSF)and raw material method was investigated.The fermentation cycle of SHF method was 24 h.The final product ethanol concentration was 102.1 g/L,the starch conversion rate was 84.9%,and the SSF fermentation cycle was 28 h.The final product ethanol concentration was 104.2 g/L,the starch conversion rate was 86.5%,and the raw material fermentation cycle was 32 h.The final product ethanol concentration was 98.9 g/L and the starch conversion was 82.2%.For the three process cost calculations,the total cost of the SHF,SSF and raw meal methods is 5799 yuan,5606 yuan,5583 yuan,The SSF fermented rice has high yield and starch conversion is more thorough,The cost of this method is low and suitable for industrial production of ethanol.Finally,the experiment showed that the raw materials mixed with rice husks showed better high temperature resistance.Yeast have better metabolic activityat high temperatures,but cells will undergo decay more easily.In the seed culture medium supplemented with rice husk,the yeast cell aggregation was observed by microscope,and the OD value of the seed liquid was generally smaller than that of the unshelled experimental group,indicating the adsorption of rice husk on yeast.In the bioreactor,the uncooked material fermentation was carried out at 39°C.The experiments indicate that the more rice husks were added,the higher the yield of ethanol.Without rice husks,no ethanol is produced.50.6 and 81.6 g/L ethanol were obtained by addition of 5 and 10 g/L rice husks,respectively.The ethanol concentration produced by fermentation at the original temperatureare was similar to that of fermentation of 39? with addition of rice husks.The results indicate that the addition of rice husks is helpful for yeast cells condensation,so yeast could resist high temperature stress.In summary,it is feasible to conduct the SSF fermentation by use of whole rice powder.On the one hand,this process save raw material costs.On the other hand,the presence of rice husks powder can improve the heat resistance of yeast.This promises the advantages of high temperature fermentation.Moreover,the SSF fermented rice has high concentration and starch conversion and utilization is more thorough,which is suitable for industrial production of ethanol.