【作者】 杨雪；

【导师】 李晓然；

【作者基本信息】 昆明理工大学 ， 生物工程（专业学位）， 2018， 硕士

【摘要】 牛乳巴氏消毒法是法国科学家巴斯德于1865年发明,以鲜牛乳为原料,通过巴氏消毒法,即在75-90~oC条件下加热10-15秒,杀灭其中有害微生物,最大限度保留鲜牛乳中的营养成分和良好口感。在发达国家市场上,巴氏乳一直是液态牛乳的主流产品,饮用巴氏乳的人口比例超过85%,巴氏乳保质期多为2-7天,因此巴氏乳的运输和保存均需要完整的冷链物流体系,以保证其营养价值和新鲜口感,这一点极大地限制了巴氏乳品在全国尤其是不发达农村地区的推广。云南发展奶业历史久远,并且有很大的发展潜力,但是巴氏鲜奶在云南省乳品消费中仅占10%左右,低于我国20%的平均水平,也因此成为云南省的乳企之间进行相互竞争的突破口。但是,巴氏杀菌法并不能完全杀灭原料乳及生产过程中的微生物,它们一方面通过生长繁殖破坏原料乳的营养成分,并引起牛乳变味,甚至可能引发因食源性病原菌所导致的食品安全问题。食源性病原菌是引发乳制品安全问题的首要原因和最大威胁,乳制品在生产包装运输过程中一旦受到食源性病原菌污染,或杀菌不彻底,它们便会借助乳制品特殊的营养物质,大量而快速地生长繁殖,从而引起乳制品腐败变质,由此不但会缩短乳制品的保质期,更会降低乳制品的质量,严重时还会造成食物中毒。巴氏乳中存在的微生物由于巴氏乳的生产环境和加工工艺的不同,在腐败过程中的微生物变化也有不同,本研究通过在实验室室温(25~oC)条件下,模拟巴氏乳的自然腐败过程,记录过程中的感官表观评定,采用基于Illumina Miseq高通量测序技术的方法研究样品在腐败过程中细菌群落结果变化规律,明确引起腐败的微生物主要为Novosphingobium、Acinetobacter和Enterococcus。通过模拟巴氏乳腐败过程明确引起腐败的主要微生物,引起巴氏乳腐败的微生物来源复杂多样,水、土壤和空气等农业环境资源的污染,以及乳牛身体的清洁和乳房卫生等均会对原料乳的质量产生影响。本实验通过对原料乳的采集环境和奶牛的生长环境进行采样并进行高通量测序,发现环境中存在的致病微生物主要为Achromobacter baumannii、Fusobacteria bacterium clone、Escherichia coli和Acinetobacter lwoffii等。在乳牛饲养阶段,注意乳牛的卫生条件和对泌乳期奶牛乳房的保护,增强对牛奶生产环境的消毒力度,由此提高原料乳的质量,为提高鲜牛乳的质量和延长货架期提供理论依据。更多还原

【Abstract】 The milk pasteurized method was invented by French scientist Pasteur in 1865.With the raw milk as raw material,the pasteurized milk was used as raw material to heat 10-15 seconds under the 75-90 o C condition to kill the harmful microorganisms,and to keep the nutrition and good taste of the fresh milk to the maximum.In the market of developed countries,pasteurized milk has always been the mainstream product of liquid milk.The proportion of drinking PAP milk is more than 85%,and the shelf life of pasteurized milk is 2-7 days.Therefore,the transportation and preservation of pasteurized milk need a complete cold chain logistics system to ensure its nutritional value and fresh taste,which greatly restricts the pasteurized milk.The promotion in the whole country,especially in less developed rural areas is difficult.The development of dairy industry in Yunnan has a long history and has great potential for development.But pasteurized milk is only about 10% in the consumption of dairy products in Yunnan Province,which is lower than the average level of 20% in China.Therefore,it has become the breakthrough of competition in Yunnan’s dairy enterprises.However,pasteurization cannot completely kill the raw milk and the microorganism in the process of production.On the one hand,they destroy the nutritional components of raw milk by growth and reproduction,and cause the flavour of milk,and even the food safety problems caused by food borne pathogens.Food borne pathogens are the primary cause and greatest threat to the safety of milk products.When dairy products are contaminated by foodborne pathogens or are not thoroughly germicidal during the process of packaging and transportation,they will grow and propagate rapidly with the aid of special nutrients in dairy products,resulting in the corruption and deterioration of dairy products.This will not only shorten the shelf life of dairy products,but also reduce the quality of dairy products.In severe cases,it will cause food poisoning.Microbes in pasteurized milk are different in the production environment and processing technology of pasteurized milk.The microbial changes in the process of corruption are also different.This study simulated the natural decay process of PAP milk in the laboratory room temperature(25o C),the sensory evaluation in the recording process,and the use of high pass based on Illumina Miseq.The method of quantitative sequencing was used to study the variation of bacterial community results during the process of corruption,and the main causes of corruption were Novosphingobium,Acinetobacter and Enterococcus.By simulating the corruption process of pasteurized milk,the main microorganisms that cause corruption have caused the complex and diverse sources of microorganism in the PAP milk corruption,the pollution of water,soil and air and other agricultural environmental resources,as well as the cleanliness of the dairy cattle and the breasts hygiene and so on.By sampling the collecting environment of raw milk and the growth environment of dairy cows and sequencing the high flux,we found that the main pathogenic microbes in the environment were Achromobacter baumannii,Fusobacteria bacterium clone,Escherichia coli and Acinetobacter lwoffii.In the feeding stage of dairy cattle,we should pay attention to the hygienic conditions of dairy cattle and protect the breasts of lactating cows,enhance the sterilizing intensity of milk production environment,thus improve the quality of raw milk,and provide a theoretical basis for improving the quality of fresh milk and prolonging shelf life.更多还原