【作者】 李除夕；

【导师】 董明盛；

【作者基本信息】 南京农业大学 ， 食品科学， 2008， 硕士

【摘要】 豆腐富含蛋白质、不饱和脂肪酸和微量元素,深受人们喜爱。但是在生产、运输和贮藏过程中因为微生物的生长繁殖导致产品的腐败,一直是困扰生产者的一个重要问题,同时引发的豆制品食品安全问题是消费者最为关注的。目前,应用数学模型预测豆腐的货架期是提高产品安全监控水平的有效措施之一,而在豆腐中一直没有相关的研究。本论文首先以豆腐为试验材料,从其腐败过程中分离纯化得到4株主要腐败细菌,结合菌株形态学特征、生理生化性状、16S rDNA序列分析确定其种类。然后研究其影响豆腐品质的微生物效应,找出特定的腐败菌,建立科学的品质预测模型,为豆腐生产、流通和销售过程中的品质和安全监控提供理论依据和技术支持。具体研究内容和结果如下:1豆腐贮藏过程中主要腐败菌的分离与鉴定从4个不同品牌的豆腐中分离得到4株优势微生物FM-1、FM-2、FM-3、FM-4。结合菌株形态学特征、生理生化性状、16S rDNA序列分析和根据MEGA3.1软件得到系统发育树等。确定FM-1属稳杆菌属Empedobacter,FM-2、FM-3属吉氏库特氏菌Kurthia gibsonii,FM-4属蜡样芽孢杆菌Bacillus cereus。2豆腐品质变化的微生物效应及其特定腐败菌的判别把分离得到的4株优势微生物分别接种到豆腐的表面,包装后在25℃下贮藏,分别于0h、4h、8h、12h、16h、20h、24h取样,分析不同指标的变化并进行感官评定,研究不同微生物对产品腐败的微生物效应。结果表明,不同微生物对产品的腐败品质的影响不同,且微生物的数量与产品的腐败程度并不完全一致。结合表观指标和品质指标,最终确定稳杆菌FM-1,库特氏菌FM-2、FM-3都是对豆腐起腐败作用的特定腐败微生物。稳杆菌属FM-1最小腐败量为6.3×10⁷cfu/g,库特氏菌属FM-2为1.38×10⁷cfu/g,库特氏菌属FM-3为10⁸cfu/g。3豆腐中库特氏菌生长动力学模型建立和货架期预测将特定腐败菌库特氏菌FM-2接种到豆腐表面,在4℃、12℃、20℃、30℃条件下贮藏,由此建立预测豆腐的微生物学品质和剩余货架期的动力学模型。结果表明,Gompertz函数能够很好的描述豆腐中的微生物生长动态,建立了4种温度下豆腐的微生物生长动力学模型。温度对最大比生长速率(μ_max)和延滞时间（Lag）的影响,采用平方根模型（Belehradek）描述呈现良好的线性关系。用豆腐在8℃和25℃的库特氏菌实测值进行验证,偏差度（B_f）和准确度（A_f）分别为1.04、1.02和1.20、1.18。获得的剩余货架期的预测模型为:SL=lag-[（8.6-N₀）/(μ_max *2.718)]*{ln[-ln（7.14-N₀）/（8.6-N₀）]-1),用豆腐贮藏在8℃和25℃的货架期实测值验证建立的模型,预测值和实测值的相对误差分别为-3.47%和4.89%,说明建立的模型能够快速可靠的预测豆腐的微生物学品质和剩余货架期。更多还原

【Abstract】 Tofu is accepted by people because it contains rich proteins,fat acids and microelements.However,the growth of contaminated microorganism which leads to the spoilage product has been become the great barrier for producer during production, transportation and preservation,and the food safety is the most attention problem for consumer.Presently,it is an effective measure of mathematics model to improve the inspect level of safety,because it can predict the shelf life of tofu.But it has no research in the tofu. In this research,we first obtained four dominant strains from spoiling tofu by traditional isolation technology and determined their species based on the characteristics of morphology,physiology,biochemistry and the 16S rDNA,Then we studied the microbial effect on the quality in order to find out the main spoilage organisms and establish the scientific quality predictive model.The aim is to provide a theory basis and technique for the inspection of quality and safety during the production,transportation and preservation of tofu.The contents and results are as follows:1 Isolation and identification of the main spoilage microorganisms in tofu during storageFour spoilage bacteria strains named FM-1、FM-2、FM-3 and FM-4 separated from four different tofu samples.Based on the characteristics of morphology,physiology, biochemistry and the 16S rDNA phylogenetic tree constructed with MEGA3.1,strain FM-1 was identified as a strain of Empedobacter,strains FM-2 and FM-3 were two strains of Kurthia gibsonii,strain FM-4 was a strain of Bacillus cereus.2 Microbial effect on the change of tofu quality and the determination of the specifics spoilage microorganismsThe four dominant microorganisms which were isolated from tofu were inoculated to the surface of tofu in order to study the microbial effect on the tofu spoilage quality.All samples were packed and preserved at 25℃and taken on 0,4,8,12,16,20,24 hours to analysis the sensory value and the changes of different indices.The result indicted that the microorganisms had significant effect on tofu spoilage quality,the microbial counts were not consistent with the tofu spoilage extent.With the apparent and character,the results from microbiological behaviors analysis,we determined FM-1,FM-2,FM-3 were the specifics spoilage microorganisms of tofu.The average numbers of FM-1,FM-2,FM-3 were 6.3×10⁷cfu/g,1.38×10⁷cfu/g and 10⁸cfu/g at the end of shelf life,respectively.3 Construction of Microbial Growth Kinetics Prediction Model of Kurthia in Tofu and shelf life predictionThe tofu was inoculated by the specific spoilage organism kurthia,then the sample was stored at 4℃,12℃,20℃and 30℃.A series of experiments had been carried out to develop and validate the growth kinetics model of kurthia for predicting the microbial quality and remaining shelf life of tofu stored in different temperature.The results from microbiological behaviors analysis showed that the kinetics models of specific spoilage organism had been developed and the growth of dynamics of this organism under 4-30℃could be well described by a Gompertz type model.And four growth models were established in tofu.The temperature dependence of Kurthia kinetic parameters-μ_max （maximum specific growth rate） and Lag phase were modeled using Belehradek（square root） model.The correlation coefficient showed could finely describe the influence of temperature on growth.Validation of built kinetic models was carried out by comparing with experimental development of kurthia grown on tofu at 8℃and 25℃.Bias and accuracy factors were used as comparison indices which were 1.04,1.02 and 1.20,1.18 respectively.The results derived from validation showed that the developed models could finely predict the growth kinetic of Kurthia at 4-30℃.The predicted model of shelf life was SL=lag-[（8.6-N₀） /(μ_max^*2.718)]^* {ln[-ln（7.14-N₀）/（8.6-N₀）]-1 },Basic errors between predicted shelf life and real shelf life were -3.47%和4.89%at 8℃and 25℃respectively,it suggested microbial growth models established in our research were valuable for rapid and realistic prediction of the microbial quality and remaining shelf life of tofu stored from 4℃to 30℃.更多还原