【作者】 于鹏；

【导师】 张兰威；

【作者基本信息】 东北农业大学 ， 食品科学与工程， 2006， 硕士

【摘要】 发酵乳以其独特的保健作用和丰富的营养以及爽口的酸味和细腻的组织状态而倍受人们欢迎，在促进人体健康和防止疾病中发挥着重要的作用，是未来功能食品发展的重要领域。在乳发酵制品的滋味与香味中，丁二酮被认为是起作用的重要化合物之一，因此如何提高发酵剂中乳酸菌代谢丁二酮能力显得尤为重要。 本课题首先对乳酸乳球菌的生长特性进行了研究，然后通过诱变育种和发酵条件优化两个方面系统的研究了如何提高乳酸乳球菌代谢丁二酮能力，最后对其增殖培养方面进行了研究，为工业化生产提供一定的依据。主要研究结果如下： 首先采用比浊法测定菌株X67的生长曲线，确定菌株X67对数生长期末期为10～12h。 然后对菌株X67进行亚硝基胍诱变。确定NTG的诱变剂量是1.25g／L处理菌株X6760min，致死率为75.5％，继续以亚硝基胍进行反复诱变，在第3轮得的NT3008产丁二酮含量最高，达0.78mg／L，比原菌株产丁二酮能力提高了13.93倍。传代实验表明该菌株遗传性质稳定。 通过单因素实验优化产丁二酮发酵条件，即确定最佳产酶温度、pH值、柠檬酸盐浓度，结果表明菌株NT3008的最佳产丁二酮发酵温度为30℃，最佳产丁二酮pH值为6.0-6.5。浓度为0.75％的柠檬酸钠能显著促进丁二酮的合成，使菌株NT-3008在优化条件下，产丁二酮能力提高到0.86mg／L。 通过单因素试验选定10％脱脂乳作为基础培养基，在此基础上通过正交试验筛选碳氮源、增殖因子，优化最佳培养基。最终确定乳酸乳球菌增殖培养基配方：脱脂乳粉10％，胰蛋白胨0.5％，酵母粉0.25％，DL-缬氨酸0.2％，柠檬酸钠1％、琥珀酸钠0.25％，硫酸镁0.05％，pH6.5，在这种培养基下经30℃，18h培养菌数达7.45×10~9CFU／mL。更多还原

【Abstract】 Fermentated milk was widely enjoyed all over the world by its particular salubrious effects, abundant nutrition, freshing sourness and tender texture. This is a promising field for development of functional foods in the future lies in its important functions on the host for its health benefit and prophylactic effects. Diacetyl is considered to be one of the most important elements in the aroma and flavor of fermentated milk. So the important aim of following scientific research should rest with how to enhance the ability of Lactococcus lactis ssp.lactis biovar diacetylactis to metabolize diacetyl.Firstly we studied the biological features of Lactococcus lactis subsp. lactis biovar diacetylactis. Then we studied how to enhance its ability of diacetyl-metabolizing by two aspects of screening and optimizing the fermentating conditions. Endly, the multiplication culture of L.diacetylactis was developed.All these offers a better basis for industrialization production. The main research results were as follows:The growth curve of strain X67 was tested by monitoring OD₆₀₀ of GM17 broth, the final period of logarithm growing of X67 was 10-12 hours.Then NTG was employed to mutate X67. When X67 was disposed by 1.25g/L NTG 60 min, its lethal rate reach 75.5%. A new strain NT3008 was obtained when strain X67 disposed continuously three times by NTG, which ability of diacetyl-producing could reach 0.78 mg/L, 13.93 times more than before. Pass-generation test showed that the heredity character of mutant strain was sTab..The fermenting conditions were optimized using single factor experiments, that is to say to confirm the optimum diacetyl producing temperature, the pH value and the concentration of the factor of the sodium citrate in fermentating culture. The optimum conditions were as follows: reaction temperature: 30℃, pH 6.5, the concentration of the sodium citrate in the culture: 0.75g/L . Under optimum conditions the diacetyl production level was at 0.86 mg/L。Endly based on single factors experiment, the optimum based cultures of L. diacetylactis was determined as 10% skim milk. And then sources of carbon, nitrogen and yeast extract power were optimized with orthogonal design, It showed that the optimal culture components of L. diacety were 10%skim milk, 0.5% pancreas peptone, 0.25%yeast extract powder, 0.2%DL-Valine, 1%sodium更多还原