Comparison of antioxidant capacity of cow and ewe milk kefirs

This research aimed to evaluate the effects of using either grain or commercial starter culture on the antioxidative capacity of cow and ewe milk kefirs. The antioxidant capacity of kefir samples during fermentation and 21 d of storage was assessed by using 3 assays: 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical cation decolorization; 2,2-diphenyl-1-picrylhydrazyl (DPPH^?) radical scavenging activity assay; and Fe⁺³-reducing power (ferric reducing antioxidant power assay, FRAP). Vitamin E and β-carotene contents were also quantified. All kefir samples exhibited varying values for DPPH, ABTS, and FRAP assays depending on the starter culture and milk type. Vitamin E and β-carotene contents were similar in all kefir samples during storage. The results of this study suggest that milk type (cow or ewe) and culture type (kefir grains or commercial starter) were the significant parameters for the antioxidative activity of kefir.     

采用电子鼻检测羊奶中的牛奶掺入

通过电子鼻系统检测在羊奶中掺入不同比例的牛奶的混合物中挥发性物质的响应值,利用主成分分析法(PCA)及线性判别分析法(LDA)对羊奶牛奶混合物的挥发性成分进行分析。结果表明:电子鼻各感应器对于原料羊乳和牛乳及杀菌羊乳和牛乳的反应值均不同。对于生奶和杀菌奶,PCA和LDA分析均能够区分羊奶中混入不同比例的牛奶,具有较好的区分性。     

Detection of cow milk in goat milk by polyacrylamide gel electrophoresis

Pasteurized goat milk was adulterated with increasing proportions of cow milk and submitted to polyacrylamide gel electrophoresis. A frontal band, missing from the pattern of genuine goat milk and possessing the same electrophoretic mobility as bovine alpha S1-casein, was expressed. The area of this zone was directly proportional to the amount of cow milk added to the goat milk.     

Structural changes in cow,goat, and sheep skim milk during dynamic in vitro gastric digestion

Coagulation of milk in the stomach is the first crucial step in its digestion. Using a human gastric simulator, the dynamic gastric digestion of goat and sheep skim milk were compared with that of cow skim milk, focusing particularly on their physical characteristics. The gastric contents were analyzed for changes in dry matter and microstructure, and the extent of protein digestion. The study revealed that the skim milk from all species formed a curd within the first 15 min of gastric digestion, at which time the pH was ~6.1 to 6.3. Compared with cow skim milk, the dry matter contents of the clots formed from goat and sheep skim milk were lower and higher, respectively, which was due to the differences in their total solids and protein contents. Microstructural analysis showed that, as digestion progressed, the clot structure became more cohesive, along with a decrease in moisture content, which in turn affected the breakdown and hydrolysis of caseins by pepsin; this phenomenon was similar for milk from all species. However, the extent of moisture retained in the sheep skim milk clot appeared to be lower than those of the cow and goat skim milk clots. In addition, the relative firmness of the sheep milk clot was higher than those of the cow and goat milk clots at the end of gastric digestion. The pattern of protein hydrolysis by pepsin was similar for the milk of all species, despite the differences in the proportions of different proteins. The study provided insight into the coagulation kinetics of goat and sheep skim milk under in vitro gastric digestion conditions.     

羊乳与牛乳理化特性比较

以莎能奶山羊羊乳为样品,利用乳样自动分析仪,氨基酸自动分析仪、等离子发射光谱、色谱分析对其基本成分、氨基酸组成及含量进行了分析和检测,并与牛乳理化特性进行比较,为科学合理地利用羊乳,生产具有独特功能的羊乳制品提供了理论依据。     

Microbial dynamics during the ripening of a mixed cow and goat milk cheese manufactured using frozen goat milk curd

To overcome the seasonal shortage of goat milk in mixed milk cheese manufacture, pasteurized goat milk curd and high-pressure-treated raw goat milk curd manufactured in the spring were held at −24°C for 4 mo, thawed, and mixed with fresh cow milk curd for the manufacture of experimental cheeses. Control cheeses were made from a mixture of pasteurized cow and goat milk. The microbiota of experimental and control cheeses was studied using culture-dependent and culture-independent techniques. Bacterial enumeration by classical methods showed lactic acid bacteria to be the dominant population in both control and experimental cheeses. In total, 681 isolates were grouped by partial amplified rDNA restriction analysis (ARDRA) into 4 groups and identified by 16S rRNA gene sequencing as Lactococcus lactis ssp. lactis (563 isolates), Leuconostoc pseudomesenteroides (72 isolates), Lactobacillus spp. (34 isolates), and Lc. lactis ssp. cremoris (12 isolates). Temporal temperature gradient gel electrophoresis (TTGE) analysis of cheese showed (1) the predominance of Lc. lactis in all cheeses; (2) the presence of Leu. pseudomesenteroides population in all cheeses from d 15 onward; (3) the presence of a Lactobacillus plantarum population in control cheese until d 15 and in experimental cheeses throughout the ripening period. Due to the most diverse and complete set of peptidases present in the genus Lactobacillus, the prevalence of this population in experimental cheeses could give rise to differences in cheese flavor between experimental and control cheeses.     

羊奶粉贮藏过程中挥发性成分的分析

采用顶空固相微萃取结合气质联用(headspace-solid phase microextraction coupled with gas chromatography-mass spectrometry,SPME-GC/MS)技术,对常温贮存下羊奶粉中挥发性成分进行提取与分析。在常温贮存1年的羊奶粉中,共检出41种挥发性成分。其中酸类成分最多,共13种,其次是酯类、烃类、醇类和醛酮类,分别为6、4、4和3种。羊奶粉的主体挥发性成分组成是丁酸、己酸、庚酸、辛酸、4-甲基辛酸、癸酸、月桂酸、邻苯二甲酸二甲酯、辛酸乙酯、十五烷、苯甲醛、甘菊环、己内酰胺,己酸、辛酸、4-甲基辛酸和癸酸在贮存6个月之后含量有明显增加趋势。在整个贮存期间,对羊奶粉膻味有较大影响的酸类物质有己酸、辛酸、4-甲基辛酸和癸酸,尤其是4-甲基辛酸,由于其较低阈值,成为最主要的羊膳物质,并且随着贮存时间的增加,酸类、酯类含量逐渐增加。     

Fungal diversity in cow, goat and ewe milk

Knowledge of fungal diversity in the environment is poor compared with bacterial biodiversity. In this study, we applied the denaturing high-performance liquid chromatography (D-HPLC) technique, combined with the amplification of the ITS1 region from fungal rDNA, for the rapid identification of major fungal species in 9 raw milk samples from cow, ewe and goat, collected at different periods of the year. A total of 27 fungal species were identified. Yeast species belonged to Candida, Cryptococcus, Debaryomyces, Geotrichum, Kluyveromyces, Malassezia, Pichia, Rhodotorula and Trichosporon genera; and mold species belonged to Aspergillus, Chrysosporium, Cladosporium, Engyodontium, Fusarium, Penicillium and Torrubiella genera. Cow milk samples harbored the highest fungal diversity with a maximum of 15 species in a single sample, whereas a maximum of 4 and 6 different species were recovered in goat and ewe milk respectively. Commonly encountered genera in cow and goat milk were Geotrichum candidum, Kluyveromyces marxianus and Candida spp. (C. catenulata and C. inconspicua); whereas Candida parapsilosis was frequently found in ewe milk samples. Most of detected species were previously described in literature data. A few species were uncultured fungi and others (Torrubiella and Malassezia) were described for the first time in milk.     

Survival of Listeria monocytogenes during manufacture, ripening and storage of soft lactic cheese made from raw goat milk

Soft lactic cheeses were manufactured with raw goat milk inoculated with Listeria monocytogenes. The physico-chemical and microbiological characteristics of curds and cheeses were determined after each processing step as well as during ripening and refrigerated storage. The fate of Listeria monocytogenes was evaluated by enumeration on PALCAM agar and by a qualitative detection after a double selective enrichment procedure. The results showed that the physico-chemical and microbiological characteristics of lactic cheeses caused a decrease of Listeria monocytogenes counts. However, this decrease did not lead to the complete disappearance of the pathogen and Listeria monocytogenes was able to survive in soft lactic cheeses made with raw goat milk.     

高通量测序方法分析冰鲜鸡肉保鲜期间微生物菌相变化研究

目的分析冰鲜鸡保鲜期间微生物菌相(细菌和真菌)的变化。方法采用高通量(16srDNA high-throughputsequencing)技术对冰鲜鸡保鲜期间微生物菌相多样性及丰富度进行分析。结果研究结果表明:冰鲜鸡在保鲜期间微生物菌相多样性及丰富度总体上呈先上升后下降的趋势。在保鲜初期,细菌(Cellulosimicrobium、 Vagococcus、 Serratia)的相对丰度水平均呈下降趋势;在保鲜的中后期,假单胞菌(Pseudomonas)的相对丰度急剧增加,成为优势菌。真菌主要为担子菌门(Basidiomycetes)与子囊菌门(Ascomycetes),其中子囊菌门(Ascomycetes)最丰富;保鲜期间曲霉(Aspergillus)、白蚁(Termitomyces)和镰刀菌(Fusarium)为优势菌属。结论冰鲜鸡保鲜期间Pseudomonas急剧增加,为优势腐败菌。     

山羊奶与牛奶和人奶营养成分的比较

对山羊奶、牛奶和人奶中蛋白质、脂肪、维生素、矿物质等主要营养成分进行了比较,分析了3种奶中主要营养成分的差别。通过比较发现,山羊奶在总体营养成分方面优于牛奶,更接近人奶。但山羊奶存在铁、叶酸和维生素B12含量较低以及羊奶膻味的问题,应在营养上对这方面加以重视。     

Viscosity changes during rennet coagulation of Murciano-Granadina goat milk

The viscosity changes during coagulation of raw and pasteurized Murciano-Granadina goat milk with 10 rennets and coagulant enzymes were studied using a cylindrical rotational viscometer. The effect of three shear rates (7.32, 14.68, 73.42 s^-1) was analysed in reconstituted milk using 60% chymosin rennet and different enzyme concentrations. The shear rate selected (14.68 s^-1) corresponded to that in which the coagulation time was not modified. At a sheer rate of 73.42 s^-1 there was a significant difference (p < .05) in the milk clotting time determined compared with the shear rates of 7.32 and 14.68 s^-1. At the beginning of the coagulation process there was a decrease in the viscosity value, which was higher in raw milk (22%) than in the two heat treated samples (17% in milk pasteurized at 65°C for 30 min, low temperature long time, and 19% in milk pasteurized at 75°C for 15 s, high temperature short time). After this period the viscosity rose rapidly and reached a value 2.89 times greater than at time 0. A highly significant Pearson correlation (0.952-0.994) was found between the coagulation time determined by the Berridge method and viscometric measurement in raw and pasteurized milk.     

牛羊乳酪蛋白制备及电泳分析比较

采采用新鲜和复原的牛羊乳为原料,等电点沉淀,通过洗涤、干燥等步骤分别制得牛乳和羊乳酪蛋白,用凯氏定氮法对其进行定量检测,应用十二烷基硫酸钠聚丙烯酰胺凝胶电泳（SDS—PAGE）分析比较牛羊乳酪蛋白组分差异。结果表明：牛乳酪蛋白得率为86．75％,羊乳酪蛋白得率为90．55％,高含量的酪蛋白主要集中在电泳图谱的中分子量组,可分为ds,CN、as2-CN、β-CN和K—CN,牛羊乳as2-CN分子量羊乳大于牛乳,牛乳a-CN含量比较多,羊乳β—CN含量比较多,鲜乳与复原乳全蛋白主要组分在电泳图谱中除酪蛋白差别外,上端的高分子量组清蛋白区羊乳IgG重链的分子量比牛乳小。应用蛋白质电泳分析技术可以区分羊乳和牛乳的蛋白质组分,等电点沉淀法制备酪蛋白的方法简单,易于操作。     

屋顶奶贮藏期品质变化的研究

研究了市售屋顶型纸盒包装纯鲜牛奶（以下简称“屋顶奶”）开封后在不同温度下（0、4、7℃）贮藏过程中微生物、脂肪质量分数和滴定酸度等指标的变化。结果表明,在不同的贮藏温度下，微生物数量在开始的5d内变化不大，到贮藏后5d则不断增加；脂肪质量分数在起始的2～3d内基本稳定，随后几天逐渐下降；酸度在起始的3则内出现下降趋势，在随后的3～5d出现波动，接着又出现回升。总之，随着贮藏温度的升高，屋顶奶品质变化进程加快，但在贮藏期内以上指标均达到质量标准。     

水牛乳中可培养乳酸菌多样性分析

采用传统分离培养方法,从三品杂交生水牛奶混合样品中,分离出105株乳酸菌,通过形态、生理生化、API细菌鉴定系统及16S rDNA基因序列分析方法对各菌株属种进行鉴定。16S rRNA序列分析结果显示,105株菌共分为5个属8个种,呈现较为丰富的乳酸菌多样性,具体数量分布为乳酸乳球菌21株,植物乳杆菌19株,格氏乳球菌17株,乳明串珠菌13株,食窦魏斯氏菌11株,肠膜明串珠菌8株,类肠膜魏斯氏菌6株,嗜热链球菌5株,糊精乳杆菌5株。由此可知,水牛乳中可培养乳酸菌优势菌群的主次关系为：乳酸乳球菌（Lactococcus lactis）＞植物乳杆菌（Lactobacillus plantaru）＞格氏乳球菌（Lactococcus garvieae）＞乳明串珠菌（Leuconostoc lactis）＞食窦魏斯氏菌（Weissella cibaria）,此为后续开发水牛乳中优势乳酸菌资源提供了良好的理论基础。     

顶空固相微萃取-气质联用法分析羊乳和牛乳中挥发性化合物

采用顶空固相微萃取技术对羊乳和牛乳挥发性化合物进行萃取,再经气相色谱-质谱联用仪检测。从羊乳中共检出49种挥发性化合物,主要由酸类、烃类、酮类和芳香族类化合物组成;牛乳中共检出33种挥发性化合物,主要由酸类、烃类、醇类和酮类化合物组成。羊乳和牛乳中检出22种相同化合物,其中酸类7种、烃类4种、芳香族类3种、酯类2种、酮类2种、醇类1种、醛类1种和其他类2种。羊乳中的挥发性成分,尤其是挥发性酸类化合物比牛乳更为复杂。     

冷藏中低聚果糖对发酵乳中微生物的影响

对添加低聚果糖的原料奶，使用嗜酸乳杆菌、双歧杆菌和嗜热链球菌作为快速发酵剂进行发酵后．在4℃条件下储存42d。每周对发酵乳进行微生物分析和酸度测试。结果表明，低聚果糖质量浓度在10—50g／L时对嗜酸乳杆菌和嗜热链球菌的存活都没有太大影响。双歧杆菌活菌数下降幅度比嗜酸乳酸杆菌和嗜热链球菌要快。但添加低聚果糖对双歧杆菌的存活起到重要作用。结论是低聚果糖产品对双歧杆菌有益生作用，因此在冷藏发酵乳制品中有助于提高双歧杆菌活菌数。     

巴氏消毒乳储存过程中化学与微生物变化

通过研究不同储存温度的巴氏消毒乳感官品质、生化指标和微生物数量,来确定影响巴氏消毒乳品质的主要因素。结果表明,在5 d的储存期内,巴氏消毒乳在4℃和8℃储存条件下感官品质变化趋势几乎一样,在12℃储存条件下感官品质下降趋势较4℃和8℃储存条件下快。巴氏消毒乳中脂肪酶的活力、TBARS值和蛋白水解程度均随着储存时间的延长而逐渐升高,SDS-PAGE显示主要蛋白未见明显分解,金黄色葡萄球菌未检出,嗜冷菌的数量逐渐减少,菌落总数呈现对数生长趋势并在储存的第4天达到稳定期。巴氏消毒乳中残存的脂肪酶、蛋白酶和微生物是影响巴氏消毒乳品质的主要因素。     

冷冻干燥对牛乳脂肪酸及异构体成分的影响

通过薄层色谱、气相色谱检测方法,对呼和浩特地区牛乳以及其冷冻干燥样的脂肪酸组成进行检测分析,结果新鲜牛乳和其冷冻干燥样品的饱和脂肪酸、不饱和脂肪酸以及共轭亚油酸含量极为相近。冷冻干燥对牛乳脂肪酸及异构体成分基本没有影响。