Production Of Nisin And Lactic Acid From Corn Stover Andstarch Through Simultaneous Saccharification And Fermentation

There will be generated about 2×1011 tons of biomass feedstock per year in the global, and the world,s energy consumption accounted for 14% of the world’s total energy consumption currently, second only to oil, coal and natural gas, ranked No. 4. In developing countries, biomass energy consumption reached more than 50%. Lignocellulose and starch are the most widely uesd biomass energy. The composition of starch is relatively simple and is formed by a glucose residues connected by α-4-glycosidic bond. The composition of cellulose is more complex that is composed of cellulose, hemicellulose and lignin, which makes the use of lignocellulosic feedstock limited. The development and utilization of biomass energy using modern technology have great significance to promote social and economic development and the improvement of ecological environment.This thesis is divided into three parts, respectively regarding to optimization of fermentation conditions of corn stover, pretreatment and optimization of starch fermentation conditions. The first part was utilized steam explosion straw as substrates and using Lactococcus lactis(Lactococcus lactis subsp. Lactis ATCC 11454) for simultaneous saccharification and fermentation. To generate the potency of nisin and lactic acid concentration as the standard amount. The substrate concentration, enzyme concentration, initial pH value and nitrogen concentration were dicussed respectively by calculating the concentration of nisin and lactic acid generated. The results showed that the optimum substrate concentration was 3%, enzyme concentration was 25FPU/g cellulose, initial pH value of 6.0, nitrogen concentration was 10g/L. Simultaneous saccharification and fermentation was conducted under optimal conditions, the highest nisin titer was 1428.35IU/ml and the maximum concentration of lactic acid was 10.64g/L. This section also fully proved that the feasibility of use bioenergy to produce two product nisin and lactic acid simultaneously.In the second part, four different pretreatment methods were used to carry out the pretreatment of corn stover. The results of the analysis of the components, the enzymatic hydrolysis and the simultaneous saccharification and fermentation were compared respectively. In the component test, the content of cellulose is the main testing standard. The results showed that the content of cellulose in corn stover was changed and the content was similar, but the content of hemicellulose and lignin were different between the four pretreatment methods. Through saccharification and simultaneous saccharification and fermentation using different pretrreated corn stove respectively, it was concluded that NaOH treatment is the best method that by calculating glucose concentration and two kinds of product concentration generated, the highest saccharification rate reached 93%, the maximum nisin titer and lactic acid concentration were 1889IU/ml 13.41g/L.In the third part, another common biomass energy- starch was used as substrate for the production of nisin and lactic acid. In order to optimize the fermentation process, the effects of starch concentration, enzyme concentration, the concentration of CaCO3, and the amount of Tween-80 on the formation of lactic acid and lactic acid were studied. The results showed that the optimum substrate concentration was 40g/L, the enzyme concentration was 100U/g, the concentration of CaCO3 was 2.5% and the Tween-80 concentration was 1ml. By using the above conditions the highest titer of nisin was 2516.42IU/ml, and the concentration of lactic acid was 37g/L, which reached 84% of the theoretical yield.