不同热加工工艺对巴氏杀菌乳中乳清蛋白的影响

以牛乳乳清蛋白为研究对象,探究不同热加工工艺（72 ℃/15 s、75 ℃/15 s、80 ℃/15 s、85 ℃/15 s）对巴氏杀菌乳乳清蛋白中3 种活性蛋白（α-乳白蛋白、β-乳球蛋白和乳铁蛋白）的影响,以及测定并分析杀菌温度对各样品菌落总数和嗜冷菌的影响。结果表明：随着热加工强度的提升,牛乳中的菌落总数随之减少,当杀菌温度在80 ℃以上时牛乳中的菌落总数小于10 CFU/mL;当杀菌温度在72 ℃以上时样品中的嗜冷菌数均小于10 CFU/mL;72 ℃/15 s 和75 ℃/15 s对α-乳白蛋白、β-乳球蛋白和乳铁蛋白影响较小,当杀菌温度达到80 ℃以上时,巴氏杀菌乳中的α-乳白蛋白、β-乳球蛋白和乳铁蛋白含量显著下降（P＜0.05）。综上,热加工的时间和温度与乳清蛋白的关系密切,72～75 ℃/15 s 的热加工工艺能更好地保留乳清蛋白中的3 种活性蛋白。     

免疫乳中IgG热变性动力学研究

对免疫乳中IgG的热稳定性及热性动力学进行了研究。结果表明,IgG的热变性属于1.2级反应。在65,70,75及80℃条件下,IgG变性的D值分别为769.23,185.18,21.55和5.09min,在此温度范围内IgG变性的Z值为6.69℃,表观活化能为345.69kJ/moL。依据IgG热变性动力学方程计算,63℃、30min杀菌,IgG变性率为3.94%;在72℃、30s,75℃、15s及85℃、5s条件下杀菌,IgG变性率分别为0.36%、0.52%和5.05%,UHT处理（120℃、0.4s)IgG全部失活。这些结果说明,乳品工业中常用的LTLT和HTST巴氏杀菌对免疫乳中IgG活性影响较小,但不可采用UHT工艺。     

不同巴氏杀菌处理对绵羊乳总蛋白及乳清蛋白二级结构的影响

目的: 分析不同巴氏杀菌处理下绵羊乳蛋白的结构变化,同时以牛乳为对照,比较二者差异性。 方法 :分别以低温长时巴氏杀菌（65 ℃ 30 min）、高温短时巴氏杀菌（85 ℃ 15 s）和超巴氏杀菌（121 ℃ 5 s）对绵羊乳、牛乳进行杀菌处理,探究巴氏杀菌处理对绵羊乳和牛乳总蛋白及乳清蛋白二级结构的影响。 结果: 3种巴氏杀菌处理均会影响绵羊乳总蛋白和乳清蛋白二级结构,改变乳蛋白原空间结构;相比总蛋白,乳清蛋白二级结构稳定性受热处理影响更大（P＜0.05,超巴氏杀菌处理对绵羊乳总蛋白与乳清蛋白二级结构影响最大,乳清蛋白变性程度最大。绵羊乳与牛乳在3种巴氏杀菌处理方式下蛋白二级结构的变化规律略有差异。 结论: 3种巴氏杀菌处理下低温长时巴氏杀菌绵羊乳蛋白结构及组成变化最小,且绵羊乳总蛋白与乳清蛋白二级结构的变化规律与牛乳略有不同,在绵羊乳液态奶加工时应引起足够重视。     

巴氏杀菌对原料羊乳卫生质量的影响

本文就巴氏杀菌条件对原料羊乳和贮存过程中巴氏杀菌羊乳的菌落总数和大肠菌群变化规律进行研究。不同污染程度的原料羊乳分别在63℃/30min、72℃/30s和85℃/15s下处理,乳样中菌落总数和大肠菌群变化差异极为显著(p<0.05)。随着巴氏杀菌强度的增大,污染程度相同乳样的巴氏杀菌效率依次增高,污染程度不同乳样的巴氏杀菌效率却依次降低。巴氏杀菌后轻度污染和中度污染的乳样在5℃贮存7d后,其菌落总数和大肠菌群变化不显著(p>0.05),均未超过巴氏杀菌乳国标GB19645-2010;重度污染的巴氏杀菌羊乳乳样在5℃贮存7d之后其菌落总数和大肠菌群已经显著超过巴氏杀菌乳国标GB19645-2010。因此原料羊乳在生产和贮存运输过程中要避免被微生物所污染,轻度和中度污染乳样的巴氏杀菌条件应选63℃/30min,贮存温度和时间应该控制在5℃/7d以内,以提高巴杀羊乳的品质和货架期。     

基于下一代测序技术分析巴氏杀菌乳中残留细菌在贮藏期间的动态变化

采用高通量测序技术,分析巴氏杀菌乳在常见贮藏温度0、4、10 ℃条件下分别贮藏0、3、6、9、12、15 d内细菌16S rRNA的V3-V4区基因序列,进而比较不同贮藏条件下巴氏杀菌乳中微生物的群落组成及动态变化。结果共获得1 887 个可操作分类单元,共检测到支原菌属（Mycoplasma）、草酸杆菌属（Oxalobacteraceae）、假单胞菌属（Pseudomonas）、不动细菌属（Actinetobacter）、链球菌（Streptococcus）等34 类细菌菌属。多样性分析表明,不同贮藏温度条件下巴氏杀菌乳中微生物的组成及多样性在门、属水平上有明显差异。在0 ℃贮藏15 d内的巴氏杀菌乳微生物多样性保持最完整,并且0 ℃其营养品质也保持较好;而在4、10 ℃贮藏期间巴氏杀菌乳的微生物多样性及营养品质都有较大影响,菌群构成及优势菌群都发生了变化,主要菌群也随贮藏温度的升高变为假单胞菌属、气单胞菌属等。研究表明,在4 ℃贮藏3 d和9 d、10 ℃贮藏6 d作为巴氏杀菌乳品质腐败的关键时间点,都出现了之前未被检测出的类芽孢菌属（Paenibacillus）、沙雷氏菌属（新Serratia）,初步推测此两种菌属是导致巴氏杀菌乳品质腐败的关键决定因素。     

不同巴氏杀菌处理对绵羊乳热加工特性的影响

目的探究绵羊液态乳的热加工特性。方法以牛乳为对照,分别通过低温长时杀菌((65±2)℃/30 min)、高温短时杀菌(85±2)℃/15 s)和超巴氏杀菌((121±2)℃/5 s)对绵羊乳进行杀菌处理,分析3种巴氏杀菌方式对绵羊乳pH值、黏度、蛋白沉淀量、酪蛋白粒径、zeta电位的影响,评价其热稳定性。结果相比于未处理组,3种巴氏杀菌处理均会显著增加绵羊乳pH值,超巴氏杀菌处理会引起绵羊乳黏度及蛋白沉淀量显著增大(P0.05);在高温短时和超巴氏杀菌处理下,绵羊乳酪蛋白粒径显著增加(P0.05),分别达到185.33 nm和242.70 nm。不同巴氏杀菌绵羊乳间Zeta电位无显著性差异;在同样处理条件下,牛乳黏度、蛋白沉淀量及酪蛋白粒径变化程度均小于绵羊乳。结论绵羊乳热加工特性较牛乳脆弱,加工温度易引起品质劣变,低温长时杀菌方式对绵羊乳的理化特性影响最小。     

牦牛血中免疫球蛋白热变性动力学的研究

研究了免疫球蛋白的热稳定性及热变性动力学,结果表明:牦牛血IgG的热变性属于0级反应。在65、70、75、80、85℃条件下,IgG变性的D值分别为722.41、311.65、17.8、5.24、2.73、1.89min,在此温度范围内IgG变性的Z值为7.9℃,表观活化能为271.25kJ/mol。依据IgG热变性动力学方程计算,63℃30min杀菌,IgG变性率为2.79%;在72℃30s,75℃15s及85℃5s条件下杀菌,IgG变性率分别为0.58%、0.66%和3.03%,UHT处理(120℃4s)IgG活性全部丧失。这些结果说明,LTLT和HTST巴氏杀菌对牦牛血中IgG活性影响较小,但不可采用UHT工艺。     

超巴氏杀菌对牛乳酪蛋白微观结构及凝聚性质的影响

以未经过热处理以及两种常用巴氏杀菌(65℃30 min、72℃15 s)处理的牛乳为对照,探究超巴氏杀菌(121℃5 s)处理对牛乳中酪蛋白微观结构及凝聚性质的影响。粒径分析结果表明,超巴氏杀菌后酪蛋白粒径明显增加;透射电子显微镜和扫描电子显微镜的分析结果表明,超巴氏杀菌能够破坏酪蛋白胶束结构,产生大规模的交联和凝聚,但是凝聚作用能够使酪蛋白胶束呈现出更均一的状态;差示扫描量热法的分析结果表明,超巴氏杀菌处理的样品,其酪蛋白胶束的变性温度略高于未经过热处理的对照组,72℃15 s处理后的酪蛋白与其他3组相比热稳定性提高,其变性温度为99℃。     

加工方式对羊乳中类胰岛素生长因子I浓度的影响

采用双抗体夹心酶联免疫法测定羊乳中类胰岛素生长因子I(IGF-I)的浓度,主要研究了巴氏杀菌、超高温灭菌、搅拌、均质以及发酵等加工方式对羊乳中IGF-I浓度的影响。研究结果表明,巴氏杀菌可使羊乳中IGF-I的浓度降低,但72℃/15 s巴氏杀菌条件对羊乳中IGF-I浓度的影响相对较小;137℃/2 s超高温灭菌条件对羊乳中IGF-I浓度的影响较大;均质和搅拌对羊乳中IGF-I的浓度基本无影响;发酵会使羊乳中IGF-I的浓度显著降低。因此,在开发富含IGF-I的功能性羊奶产品时,可选择72℃/15 s的巴氏杀菌条件,生产中均质和搅拌2种加工方式均可以采用,但不宜将其发酵成酸奶制品。     

DHA藻油在调制乳中的稳定性研究

通过对添加DHA藻油调制乳生产工艺的研究,采用L_9(3~4)正交试验的方法,确定最佳工艺条件为V_C-Na添加量0.30 g/kg,巴氏杀菌参数85℃/15 s,储存温度10℃,储存时间≤6 h,产品稳定性最好。     

常见热杀菌方式对关中羊乳品质的影响

采用5种常用热杀菌方式处理关中羊乳,即低温长时巴氏杀菌(65 ℃/30 min)、高温短时巴氏杀菌(72 ℃/15 s)、超巴氏杀菌(95 ℃/5 min)、高温高压灭菌(121 ℃/20 min)和超高温瞬时灭菌(137 ℃/7 s),在测定蛋白沉淀率、酒精稳定性、pH、红度值、粘度和脂肪球变化基础上,结合内源荧光光谱和聚丙烯酰胺凝胶电泳(SDS-PAGE)分析,探究热杀菌处理对关中羊乳品质的影响。结果表明,高温高压灭菌羊乳蛋白沉淀率最高、酒精稳定性最差、pH明显下降、红度值明显增大,但5种杀菌方式对粘度没有显著影响(p>0.05);羊乳脂肪球经巴氏杀菌和超巴氏杀菌后,表观直径略微增大,而高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌则导致其明显变小;荧光光谱表明,高温高压灭菌羊乳蛋白结构改变最大,内源荧光强度剧烈升高;电泳显示,巴氏杀菌(65 ℃/30 min和72 ℃/15 s)对羊乳酪蛋白和乳清蛋白影响较小,超巴氏杀菌(95 ℃/5 min)乳清蛋白开始变性、聚集或部分降解,高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌则使乳清蛋白明显降解甚至消失,酪蛋白出现聚集和解聚。结果表明,高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌对关中羊乳品质影响较大,超巴氏杀菌影响次之,而巴氏杀菌则对其影响较小。     

牛乳中反式脂肪酸在不同热处理条件下的含量变化及热杀菌工艺评价

目的：探讨牛乳中反式脂肪酸(TFA)在不同热处理条件下的变化规律,为工艺参数确立提供依据。方法：采用罗兹-哥特里法提取乳中脂肪,经甲酯化反应后进行气相色谱分析,对牛乳中的TFA含量进行分析比较。结果：在85℃条件下,随着加热时间的延长,牛乳中TFA含量呈显著上升趋势(P＜0.05);相同时间内在超高温(T＞133℃)条件下,提高灭菌温度,牛乳中TFA含量变化不大(P＞0.05);延长灭菌时间,TFA含量明显增加(P＜0.05)。结论：以减少TFA生成量为主要依据确立的巴氏杀菌工艺参数是：85℃、15s;UHT工艺参数为(137±2)℃、4s。     

One-step isolation of lactoferrin using immobilized monoclonal antibodies

Immunoaffinity columns made with monoclonal antibodies to either human or bovine lactoferrins were prepared to isolate human lactoferrin or bovine lactoferrin from milks by a single chromatographic step. Recoveries of human lactoferrin and bovine lactoferrin were 98 and 97%, respectively. The human lactoferrin recovered from defatted human colostrum was 98% pure with 93% iron-binding capacity. Amount of recovered bovine lactoferrin, as well as purity and iron-binding capacity, varied widely depending on the source of bovine milks and pretreatments (particularly pasteurization temperature). The best source to isolate bovine lactoferrin was raw skim milk yielding a protein 97% pure and with a 99% iron-binding capacity. Thus, immunoaffinity chromatography provides an effective one-pass isolation of highly pure human or bovine lactoferrin with reasonable recovery and iron-binding capacity.     

Proteomic study on the stability of proteins in bovine,camel, and caprine milk sera after processing

Milk proteins have been shown to be very sensitive to processing. This study aims to investigate the changes of the bovine, camel, and caprine milk proteins after freezing, pasteurization (62 °C, 30 min), and spray drying by proteomic techniques, filter-aided sample preparation (FASP) and dimethyl labeling followed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). A total of 129, 125, and 74 proteins were quantified in bovine, camel, and caprine milk sera, respectively. The milk serum protein content decreased significantly after freezing, pasteurization, or spray drying, which can be ascribed to the removal of protein aggregates by the pH adjustment and ultracentrifugation during sample preparation. Some of the immune-related proteins were heat-sensitive, such as lactoferrin (LTF), glycosylation-dependent cell adhesion molecule 1 (GLYCAM1), and lactadherin (MFGE8), with losses of approximately 25% to 85% after pasteurization and 85% to 95% after spray drying. α-Lactalbumin (LALBA), osteopontin (SPP1), and whey acidic protein (WAP) were relatively heat stable with losses of 10% to 50% after pasteurization and 25% to 85% after spray drying. The increase of some individual proteins in concentration after freezing may be caused by the proteins originating from damaged milk fat globules and somatic cells. GLYCAM1 decreased significantly after pasteurization in bovine and camel milk but this protein is relatively stable in caprine milk. In conclusion, milk proteins changed differently in concentration after different processing steps, as well as among different species.     

Does beta-lactoglobulin occur in human milk?

Although beta-lactoglobulin (beta-lg) has been considered to be absent from human milk, recent results of other workers, based on immunological reactions between human milk and rabbit antiserum to bovine beta-lg, suggest that this protein may be present. Although our results show similar immunological reactions, we consider that lactoferrin is responsible for these, as it was the only reactive protein species which could be prepared to homogeneity. Indeed two types of antibodies were found by ELISA test in the antisera to bovine beta-lg. One of them would be able to bind loosely to human lactoferrin, but its binding sites would not be antigenic in the rabbit.     

The influence of pasteurization temperature on the physicochemical composition and colour of Murciano-Granadina goat milk

An evaluation of the physicochemical characteristics and colour in Murciano-Granadina goat milk was carried out on several samples subjected to different pasteurization treatments (72°C/15 s, 76°C/15 s and 80°C/10 s). An apparent increase in the level of caseins was observed along with a decrease in the serum protein contents at pasteurization temperatures of 76 and 80°C. This change can be partly justified by the interactions between β-lactoglobulin and K-casein in pasteurized milk. The fat content, viscosity and density of the milk showed minimal sensitivity to the thermal treatments, but the heat treatment did affect the parameters which defined the colour of the milk, as shown by a decrease in the Yellow Index and an increase in the difference in colour.     

Effect of heat treatment on the antibacterial activity of bovine lactoferrin against three foodborne pathogens

The effect of different heat treatments on the antimicrobial activity of bovine lactoferrin against Escherichia coli O157:H7, Salmonella enteritidis and Listeria monocytogenes has been studied. We have observed that the heat treatments lower than 85°C for 10 min did not affect the antibacterial activity of the protein. Hydrolysates of bovine lactoferrin were found to be more active than the native protein against the three pathogens. Moreover, the antibacterial effect of bovine lactoferrin was also assayed in milk and whey, and although we found a reduction in the number of viable cells, this reduction was lower than in culture media.     

Sporulation and Germination Gene Expression Analysis of Bacillus anthracis Sterne Spores in Skim Milk under Heat and Different Intervention Techniques

ABSTRACT:  To investigate how B. anthracis Sterne spores survive in milk under heat (80 °C, 10 min), pasteurization (72 °C, 15 s), microfiltration, and pasteurization and microfiltration, the expression levels of genes related to sporulation and germination were tested using real-time PCR assays. Twenty-seven sporulation- and germination-related genes were selected for the target genes. Our results demonstrated that gene expression levels were altered by heat and microfiltration whereas the pasteurization and pasteurization and microfiltration resulted in less alteration of gene expression. Heat activated and inhibited both sporulation- and germination-related genes, suggesting that bacterial spores underwent different molecular mechanism for heat treatments. Our results may provide some insight into the molecular mechanisms of spore survival in response to heat treatment and different intervention strategies used to treat fluid skim milk.     

含乳铁素的酸乳制品对淋巴细胞增殖的影响

本研究采用MTT法分别测定了含乳铁蛋白水解物的酸乳制品、乳铁蛋白水解物以及乳铁素对小鼠外周血单核细胞以及脾细胞的增殖影响。结果显示,含乳铁蛋白水解物的酸乳制品、乳铁蛋白水解物以及乳铁素都有不同程度的免疫刺激作用,其中乳铁素的免疫刺激作用最强。     

贮藏条件对红薯叶酸菜品质的影响

目的:探寻乳酸菌发酵红薯叶酸菜的贮藏条件及贮藏期间品质变化规律。方法:真空包装后以常温25℃、低温4℃、80℃—15 min巴氏杀菌后4℃、85℃-10 min巴氏杀菌后4℃贮藏,比较4个条件下红薯叶酸菜pH值、乳酸含量、亚硝酸盐含量、菌落数、色差值及感官评分。结果:25℃下贮藏亮度下降最快,第60天色泽明显变深;4℃下贮藏第30天的酵母菌数量最多,第45天的乳酸菌数量最多;80℃-15 min杀菌后贮藏第90天的大肠杆菌数量最少,感官评分达到食用临界值;85℃-10 min杀菌后贮藏第75天的总菌数量最少,感官评分及格。pH值与亚硝酸盐含量呈极显著负相关,与L值、感官评分呈极显著正相关;乳酸菌数与酵母菌、大肠杆菌、总菌数呈极显著正相关,其中感官评分在第一主成分中的载荷量最大。结论:80℃-15 min杀菌后4℃贮藏,其主要微生物为乳酸菌,其他指标均符合安全标准,感官品质稳定,更适合作为酸菜的贮藏条件,贮藏期可达90 d。