【作者】 张磊；

【导师】 郭爱玲；

【作者基本信息】 华中农业大学 ， 工程硕士（专业学位）， 2016， 硕士

【摘要】 鸡蛋由于营养丰富、价格便宜,因此成为了人们日常饮食生活中的重要组成部分。鸡蛋在生产、运输以及储存过程中存在着被微生物污染的隐患,微生物的污染不仅会使鸡蛋丧失食用价值,造成巨大的经济损失,更严重的还会引发食品安全问题。本研究主要就鸡蛋在不同条件储存过程中的菌落总数、微生物种类、蛋壳细菌群落关系、阻抗以及蛋品质相关性进行了研究,主要研究内容包括三个部分。第一部分:对九峰新跃养鸡场新鲜鸡蛋在常温25℃以及低温4℃储存过程中蛋壳表面、蛋清以及蛋黄菌落总数变化以及微生物种类进行了研究,同时对从蛋壳表面、蛋清以及蛋黄中分离出的微生物进行鉴定。结果表明25℃储存过程中鸡蛋蛋壳初始菌落总数对数值为2.77,鸡蛋蛋壳表面的菌落总数随着储存时间的延长而增加,菌落总数对数值变化范围为2.77-4.39;蛋黄、蛋清开始并未检测到微生物存在,20 d左右开始检测到有微生物,蛋黄、蛋清菌落总数随时间延长而增长。25℃储存过程中从蛋壳表面分离收集到的细菌总共有86种,蛋清中分离得到的细菌25种,蛋清中分离得到的细菌18种。4℃鸡蛋蛋壳初始菌落总数的对数为3.6,鸡蛋蛋壳菌落总数随时间延长呈现先增加后减少再增加的趋势,下降的原因可能是由于低温或者营养物质的减少造成的。4℃储存过程中蛋壳表面分离得到的细菌总共有74种,蛋内外分离得到的微生物较少。因此低温储存条件可以有效延缓微生物侵入到蛋内,延长鸡蛋保质期。第二部分:对鸡蛋蛋壳表面微生物进行宏基因组测序,蛋壳表面微生物宏基因组测序结果显示样品A、B共含有OTU数目为7828,其中A样品中含有OTU数目为5093,B含有OTU数目为4524,表明蛋壳表面细菌种类很多。通过对鸡蛋样品Alpha多样性分析发现蛋壳表面的细菌群落呈现多样性高的特点,蛋壳表面细菌群落结果表明蛋壳表面细菌中变形菌门和厚壁菌门所占丰度很高,样品A、B在属水平上细菌群落组成相同,但不同属细菌在丰度上存在差异。第三部分:对3种温度(4℃、25℃、37℃)和3种湿度(RH75%、RH75%、RH75%)组合下的9组不同条件储存过程中鸡蛋的哈夫单位、蛋黄指数、p H以及阻抗进行检测。结果表明哈夫单位、蛋黄指数以及阻抗随储存时间延长而减小,p H随储存时间延长上升。不同储存条件下,鸡蛋品质变化不同。温度越低、湿度越小,鸡蛋的品质更好,因此将鸡蛋放置于低温干燥的环境下保存可以适当延长鸡蛋保质期。鸡蛋在不同条件储存过程中阻抗与哈夫单位、蛋黄指数、p H3个鸡蛋品质指标之间表现出了较好的相关性,因此在一定条件下,可以考虑用阻抗来表示鸡蛋品质。更多还原

【Abstract】 Eggs are an important compnent of people’s daily life because of the rich nutrients and the cheap price.Eggs risk microbial contamination in the process of production,transportation and storage,microbial contamination will not only make the eggs lose their edible value,resulting in huge economic losses,but also lead to more serious food safety problems.In this study,the aerobic plate count,the microbial species,the bacterial community relations,the impedance and the egg quality of the eggs in different conditions were studied.The main contents of this study included three parts.The first part: Fresh eggs were obtained from the Jiufeng Xinyue farm,and the eggs were subsequently stored at room temperature nearly 25 ℃ and low temperature at 4 ℃.The clone total number of eggshell,egg white,yolk changes and egg white changes in impedance were determined,at the same time,microorganisms of the egg white and yolk were isolation and identification.The result indicated that the initial aerobic plate count was 2.77 log CFU/eggshell and the aerobic plate count of the eggshell increases with the storage time,the aerobic plate count on the eggshell on the range of 2.77-4.39.Egg yolk and egg white were not to be detected in the presence of microorganisms at the beginning,it is until 20 d to detect the presence of microorganisms,the aerobic plate count of the egg yolk,egg white increased with storage time.A total of 86 kinds of bacteria were isolated from the surface of the egg during the storage at 25 ℃,25 kinds of bacteria were isolated from the egg white,and18 kinds of bacteria were isolated from the egg white.The logarithm of the initial colony count of the shell was 3.6 when storage at 4 ℃,and the aerobic plate count of eggshell showed a trend of increasing and then decreasing,but increasing after decreasing.The reason of the decrease was due to the low temperature or the fewer nutrients.There are 74 kinds of bacteria isolated from the eggshell in the process of storage at 4 ℃,but few bacteria isolated from egg content.Therefore,the low temperature storage conditions can effectively delay the microbial invasion into eggs and extend the shelf life of eggs.The second part: using metagenomic sequencing to investigate the microorganism on the eggshell,and the result showed that the number of OTU of sample A and sample B was 7828,of which the number of OTU of sample A was5093 and the number of OTU of sample B was 4524,which indicating that the bacterial on eggshell is very rich.Through the analysis of Alpha diversity of egg samples,it was found that the bacterial community diversity was high.Result of bacterial community on Eggshell showed that the number of Proteobacteria and Firmicutes on the eggshell is the most high,and sample A and sample B has the same bacterial community composition at the genus level,but the number of different bacteria is different.The third part: There were 9 different experimental conditions after combination of three kinds of temperature(4 ℃,25 ℃,37 ℃)and three types of humidity(RH75%,RH75%,RH5%),and egg’s haugh unit,yolk index,p H and impedance were detected during storage time.The results showed that the haugh unit,yolk index and impedance decreased with storage time,and p H increased with storage time.The quality of eggs varied under different storage conditions.The lower the temperature and the smaller the humidity,the better the quality of eggs,so the eggs shelf life can be properly extended when placed at low temperature and in dry environment.Impedance of the eggs during different storage conditions showed good correlation with egg quality(haugh unit,yolk index,p H),so impedance can represent egg quality under certain conditions.更多还原