【作者】 周文娟；

【导师】 陈霞；

【作者基本信息】 扬州大学 ， 营养与食品卫生学， 2020， 硕士

【摘要】 慕斯是一种深受人们喜爱的低温乳制甜点,在慕斯中添加益生菌不仅丰富了益生菌功能食品的种类,而且可以提升慕斯的营养功能和商业价值。研究证实慕斯是益生菌生存的良好载体,但其生产、储运和消费过程中的高氧、高渗透压、低温等环境因素都会对菌体的活性产生一定的影响。大量研究表明,细菌在处于非致死性胁迫环境时,会诱导增强对同类胁迫及其他胁迫的耐受能力,产生交互适应效应。本文以慕斯为研究对象,将不同预胁迫处理的鼠李糖乳杆菌Lactobacillus rhamnosus hsryfm 1301添加到慕斯中,研究经预胁迫处理的菌株在慕斯基质中的生长特性,筛选适合益生菌慕斯生产的菌株预胁迫处理条件;并研究预胁迫处理对益生菌慕斯的品质、储藏特性、挥发性风味物质和功能特性的影响。研究结果如下:1.L.rhamnosus hsryfm 1301的最佳预胁迫处理条件的筛选利用不同强度的热、酸、渗透压和氧化对L.ramnosus hsryfm 1 301进行预胁迫处理,确定每种胁迫条件对鼠李糖乳杆菌的亚致死条件;并研究亚致死胁迫条件对L.rhamnosus hsryfm 1301的生长速度、发酵性能和酶活性的影响;并用几种亚致死胁迫条件处理后的菌株制作慕斯,比较其在慕斯中的存活率的变化,筛选出菌株的最佳预胁迫处理条件。结果表明:L.rhamnosus hsryfm 1301的亚致死胁迫条件分别为50℃-1 h、pH 2.5-3 h、3.5 mM H2O2-1 h、1.8 MNaCl-4 h。4种预胁迫处理均会对菌株的生长速度产生一定的影响,其中50℃-1 h和pH 2.5-3 h预处理菌株的对数期较对照组延长了 3 h,1.8 M NaCl-4 h预处理菌株生长速度与对照组无显著差异(P>0.05),3.5 mM H2O2-1 h预处理菌株调整期比对照组延长了 8h。分别用上述4种预胁迫条件处理L.rhamnosus hsryfm 1301后,其发酵凝乳时间均比对照组延长,其中1.8 MNaCl-4 h的凝乳时间为12.5 h,比对照组延迟了 0.5 h,50℃-1 h、pH 2.5-3 h和3.5 mM H2O2-1 h三种预处理菌株凝乳时间均为13 h,比对照组延迟了 1 h;经四种预胁迫处理后,pH 2.5-3 h组凝乳时的pH显著高于对照组,酸度显著低于对照组,其余三组的pH值和酸度与对照组均无显著差异(P>0.05);四种预处理菌株发酵乳凝乳时的活菌数均低于对照组;另外4种预处理均提高了 L.rhamnosus hsryfm 1301的β-半乳糖苷酶活力。用4种预胁迫处理的L.rhamnosus hsryfm 1301发酵乳制作益生菌慕斯,在4℃贮藏21d后,4组慕斯样品的活菌数均高于8.0 log cfu/g,其中pH 2.5-3 h组和50℃-1 h组慕斯样品L.rhamnosus hsryfm 1301的存活率比对照组分别高26.49%和 1.25%;而 3.5 mM H2O2-1h 及 1.8 M NaCl-4 h 组样品的 L.rhamnosus hsryfm 1301存活率均低于对照组;因此,选择pH 2.5-3 h和50℃-1 h作为菌株的预胁迫处理条件进行下一步的研究。2.L.rhamnosus hsryfm 1301的预胁迫处理对益生菌慕斯品质的影响用pH 2.5-3 h和50℃-1 h预胁迫处理的L.rhamnosus hsryfm 1301分别制作发酵乳,并制备慕斯,以未处理菌株制作的慕斯作为对照,研究菌株预胁迫处理对益生菌慕斯的感官品质、酸度、pH值、质构特性、流变特性和挥发性风味物质的影响。结果表明:与对照组相比,50℃-1 h组慕斯在-18℃冰箱贮藏120 d后L.rhamnosus hsryfm 1301的存活率降低了 1.41%,而pH 2.5-3 h组慕斯中L.rhamnosus hsryfm 1301的存活率提高了 0.86%,因此pH 2.5-3 h为慕斯中L.rhamnosus hsryfm 1301的最佳预处理条件。与对照组相比,pH 2.5-3 h预处理L.rhamnosus hsryfm 1301对益生菌慕斯的感官品质、硬度、粘附性、内聚性,咀嚼性、弹性和表观粘度均无显著性影响(P>0.05)。在储藏期间各组慕斯的pH值均呈下降趋势,酸度均呈上升趋势;且与对照组相比,pH 2.5-3 h组慕斯的后酸化程度更小,而-18℃冻藏比4℃冷藏后酸化更小,由此说明L.rhamnosus hsryfm 1301经过pH 2.5-3 h处理,并于-18℃贮藏更有助于改善益生菌慕斯的品质。利用GC-MS检测了不同贮藏温度慕斯中的挥发性风味物质变化,共检测出酮类、醇类、酸类、醛类和酯类5类主要挥发性成分,其相对含量由高到低依次为:酸类>酯类>醛类>醇类>酮类。pH 2.5-3h处理菌株降低了慕斯中酸类化合物的形成量,特别是降.低了乙酸的含量。3.预胁迫处理对慕斯中L.rhamnosus hsryfm 1301的胃肠道耐受性及耐药性的影响用pH 2.5-3h处理的菌株制作发酵乳,并制备慕斯,分别贮藏于4℃和-18℃,并以未处理菌株制作的慕斯作为对照,研究预胁迫处理对益生菌慕斯中的L.rhamnosus hsryfm 1301体外胃肠道耐受性和抗生素耐药性的影响。结果表明:在4℃贮藏条件下,pH 2.5-3 h组慕斯中的L.rhamnosus hsryfm 1301在人工模拟唾液和肠液中的存活率比对照组分别提高了 5.01%和13.55%,在人工胃液中的存活率与对照组无显著差异(P>0.05);-18℃贮藏的 pH 2.5-3 h 组慕斯中的L.rhamnosus hsryfm 1301 在人工模拟唾液、胃液和肠液中的存活率比对照组分别提高了 5.55%、4.84%和5.46%;说明pH 2.5-3 h预处理可以提高慕斯中L.rhamnosus hsryfm 1301对唾液及胃肠道环境的耐受性能力。另外对其抗生素耐药性的研究结果表明pH 2.5-3 h组预处理菌株对L.rhamnosus hsryfm 1301的抗生素耐药性无显著影响。更多还原

【Abstract】 Mousse is a dairy dessert with delicate taste and unique flavor,which is popular among consumers.Due to its rich nutrition and suitable for the growth of probiotics,probiotics added to mousse can not only increase the nutritional value of mousse,but also improve its market competitiveness.However,environmental factors such as high oxygen,high osmotic pressure and low temperature during production,storage,transportation and consumption all have certain effects on the viability of bacteria.A large number of studies had shown that when bacteria are in a non-lethal stress environment,they can induce and enhance their tolerance to the same type of stress and other stresses,resulting in an interactive adaptive effect.Taking mousse as the research object,L.rhamnosus hsryfm 1301 with different pre-stressed were added to the mousse to study the growth characteristics of the strains in the mousse matrix,and to screen the pre-stress treatment conditions which is suitable for probiotic mousse production.The effects of pre-stress treatment on the quality,storage characteristics,volatile flavor substances and functional characteristics of probiotic mousse were studied.The results are as follows:1.Screening of optimal prestress treatment conditions for L.rhamnosus hsryfm 1301L.rhamnosus hsryfm 1301 was pre-stressed with different intensities of heat,acid,osmotic pressure and oxidation to determine the sublethal conditions of each stress condition on lactobacillus rhamnosus.The effects of sublethal stress on the survival rate,fermentation performance and enzyme activity of L.rhamnosus hsryfm 1301 were studied.The mousse was prepared with several strains under sublethal stress conditions,and the changes of survival rate in the mousse were compared.The results showed that the sublethal stress conditions of L.rhamnosus hsryfm 1301 were 50℃-1 h,pH 2.5-3 h,3.5 mM H2O2-1 h and 1.8 M NaCl-4 h,respectively.All of the four pre-stress treatments had a certain impact on the survival rate of the strains.Among them,the logarithmic period of the pretreated strains at 50℃-1 h and pH 2.5-3 h had extended 3 h compared to the control.The survival rate of the 1.8 M NaCl-4 h had no significant difference to the control(P>0.05).The adjustment period of the pretreated strains at 3.5 mM H2O2-1 h had extended 8 h compared to the control group.After pre-treated with the above four conditions,the fermentation and curd time of the L.rhamnosus hsryfm 1301 were all prolonged compared to the control.The curd time of 1.8 M NaCl-4 h was 12.5 h,which was delayed 0.5 h compared with the control group.The curd time of 50℃-1 h、pH 2.5-3 h and 3.5 mM H2O2-1 h was 13 h,which was delayed 1 h compared with the control group.After four kinds of pre-stress treatment,the pH value of the pH 2.5-3 h group were significantly higher than the control,and acidity were significantly lower than the control(P>0.05).The viable counts of the four pretreated strains were lower than that of the control.In addition,all the four pretreatments improved the activity of beta-galactosidase of L.rhamnosus hsryfm 1301.Probiotic mousses were prepared with L.rhamnosus hsryfm 1301 fermented milk treated with four kinds of pre-stress.During the 21 days of storage at 4℃,viable counts of the four mousse samples were all higher than 8.0 log cfu/g.The survival rate of L.rhamnosus hsryfm 1301 in the pH 2.5-3 h and 50℃-1 h were higher 26.49%and 1.25%than the control group,and the survival rate of L.rhamnosus hsryfm in the 3.5 mM H2O2-1 h and 1.8 M NaCl-4 h were lower than the control.Therefore,pH 2.5-3 h and 50℃-1 h were selected as the pre-stress treatment conditions for the next study.2.Effect of pre-stress treatment of L.rhamnosus hsryfm 1301 on the quality of probiotic mousseFermented milks were prepared with L.rhamnosus hsryfm 1301 treated with pH 2.5-3 h and 50℃-1 h respectively,and the mousse was prepared.The effects of pre-stress on the sensory quality,acidity,pH value,texture,rheological properties and volatile flavor of probiotic mousse were studied with the mousse prepared,and L.rhamnosus hsryfm 1301 without any treatment was used as the control.The results showed that the survival rate of 50℃-1 h mousse storage at-18℃ for 120 d was decreaseed 1.41%compared to that of the control,and the survival rate of pH 2.5-3 h mousse was increased 0.86%compared to the control.Therefore,pH 2.5-3 h was the best pretreatment condition for L.rhamnosus hsryfm 1301 compared with the control group,the sensory quality,hardness,adhesion,cohesion,mastication,elasticity,and apprarent viscosity of pH 2.5-3 h probiotic mousse had no significant difference with the control(P>0.05).The pH value of all samples were showed a downward trend,and the acidity showed an upward trend,and the postacidification of pH 2.5-3 h was lower than that of the control,and which storaged at-18℃ was lower than 4℃.Which indicated that pH 2.5-3 h and storage at-18℃ would be more helpful to improve the quality of probiotic mousse.GC-MS was used to detect the changes of volatile flavor substances in mousse at different storage temperatures,and 5 kinds of major volatile components were detected,including ketones,alcohols,acids,aldehydes and esters were detected.Their relative contents were successively from high to low:acid>esters>aldehydes>alcohols>ketones.The pH 2.5-3 h treatment could reduced the formation of acid compounds in mousse,especially the content of acetic acid.3.Effects of pre-stress treatment on the gastrointestinal tolerance and drug resistance of l.rhamnosus hsryfm 1301 in mousseThe fermented milk was prepared with ph 2.5-3 h strain,and the mousse was stored at 4℃ and-18℃,respectively.The effect of pre-stress treatment on the in vitro gastrointestinal tolerance of L.rhamnosus hsryfm 1301 in probiotics mousse was studied,using the mousse prepared with untreated strain as the control.The results showed that the survival rate of L.rhamnosus hsryfm 1301 in the artificial saliva and intestinal juice of pH 2.5-3 h group was 5.01%and 13.55%higher than that of the control group,respectively.The survival rate in the artificial gastric juice was not significantly different from that of the control group(P>0.05).The survival rate of L.rhamnosus hsryfm 1301 in artificial saliva,gastric juice and intestinal juice of pH 2.5-3 h group storage at-18℃ was 5.55%,4.84%and 5.46%higher than that of the control group.The results indicated that pH 2.5-3 h pretreatment could improve the tolerance of L.rhamnosus hsryfm 1 301 in the mousses to saliva and gastrointestinal environment.In addition,the results of the study on antibiotic resistance showed that the pH 2.5-3 h pretreatment had no significant effect on the antibiotic resistance of L.rhamnosus hsryfm 1301.更多还原