高黏度酸化乳体系的稳定性

酸化乳口感细腻、风味独特,深受消费者的喜爱。但在加工贮藏过程中容易出现乳清析出、蛋白质沉淀、絮凝等体系不稳定问题。果胶和其他稳定剂协同作用可以使酸化乳体系稳定且口感较好。通过测定产品黏度、持水力、乳清析出率及感官特性,研究不同食品胶对酸化乳产品的影响。结果表明：果胶、海藻酸丙二醇酯（propylene glycol alginate,PGA）和羧甲基纤维素钠（carboxymethylcellulose sodium,CMC-Na）3 种胶体复配使用时,酸化乳体系黏度适中、体系稳定且口感较好。筛选出黏度合     

粒径分析法研究含乳果汁的稳定性

本文探讨了含乳果汁稳定性的机理，并采用粒径分析的方法，对含乳果汁的稳定性进行了研究，考察了乳／果汁比例、乳体系、果汁体系、稳定剂、加工条件等诸因素对产品稳定性的影响。     

美国研究酸化乳蛋白分散物与葡聚糖及硫酸葡聚糖的相互作用

<正>多糖常被用作发酵乳品的稳定剂,但两者相互作用的本质还不是很清楚。美国研究人员将葡聚糖(不带电荷)和硫酸葡聚糖(带电荷)分别添加至事先酸化的复原脱脂乳,然后在0℃放置,考察该乳蛋白分散物的相行为。结果表明:当乳固形物含量较低(5.0%~7.5%)时,不添加多糖,经过24 h贮存后也会发生相分离;添加0.7%或1.0%硫酸葡聚糖可以起到稳定作用;但乳固形物含量较高时,不发生相分离。酸化至不同pH值的样品中均观察到了相近的结果。     

嗜热链球菌对瑞士乳杆菌发酵乳后酸化的影响

瑞士乳杆菌是潜在的功能发酵乳发酵剂,为改善瑞士乳杆菌的发酵特性,使用嗜热链球菌配合瑞士乳杆菌用于发酵乳制备。结果表明：嗜热链球菌与瑞士乳杆菌混合发酵将凝乳时间缩短了3.5 h,黏度提高了1.8 倍,改善了乳清析出和质构;嗜热链球菌的使用有效减弱了发酵乳的后酸化,贮藏20 d发酵乳的pH值仍大于4.2。为研究这一现象的原因,测定发酵乳中的活菌数、乳糖消耗量、谷氨酸脱羧酶和β-半乳糖苷酶活性,结果表明,混合发酵乳贮藏期间具有较低的谷氨酸脱羧酶和β-半乳糖苷酶活性,乳糖利用量较低,这是后酸化减弱的主要原因。与嗜     

酸化乳对犊牛生长性能和血清免疫指标的影响

本试验旨在研究饲喂酸化乳对犊牛生长性能和血清免疫指标的影响。本试验采用完全随机试验设计,选择3日龄左右、体重(40±5) kg的健康荷斯坦犊牛20头,随机分为2组,即酸化乳组和巴氏杀菌乳组,每组10头。酸化乳组饲喂酸化乳,巴氏杀菌乳组饲喂巴氏杀菌乳,2组均自由采食颗粒料,试验期共180 d,在试验第60天时断奶。每天记录犊牛的采食量,于犊牛生长期的第7、30、60、90、180天分别测量体尺、体重,计算平均日增重,同时采血用于测定血清免疫指标。结果表明:1)酸化乳组乳尿素氮含量极显著高于巴氏杀菌乳组(P<0.01),乳大肠杆菌、总菌数量显著低于巴氏杀菌乳组(P<0.05),乳糖率、乳脂率和乳蛋白率组间差异不显著(P>0.05)。2)第31～50天时,酸化乳组犊牛液体饲料平均日采食量极显著高于巴氏杀菌乳组(P <0.01);第61～90天时,酸化乳组犊牛固体饲料平均日采食量极显著高于巴氏杀菌乳组(P <0.01)。3)第60～180天时,酸化乳组犊牛平均日增重显著高于巴氏杀菌乳组(P <0.05)。第60天时,酸化乳组犊牛体直长、体高和管围均显著高于巴氏杀菌乳组(P<0.05);第90天时,犊牛体直长、体斜长、体高和管围均显著高于巴氏杀菌乳组(P<0.05);第180天时,酸化乳组犊牛体直长、体斜长和体高均极显著高于巴氏杀菌乳组(P<0.01)。4)第60天时,酸化乳组血清免疫球蛋白A(IgA)含量显著高于巴氏杀菌乳组(P<0.05);第90天时,酸化乳组血清免疫球蛋白G(IgG)含量极显著高于巴氏杀菌乳组(P<0.01);第90和180天时,酸化乳组血清免疫球蛋白M(IgM)含量显著高于巴氏杀菌乳组(P<0.05)。第30天时,巴氏杀菌乳组血清肿瘤坏死因子-α(TNF-α)和白细胞介素-1β(IL-1β)含量均极显著高于酸化乳组(P<0.01),血清白细胞介素-6(IL-6)含量显著高于酸化乳组(P<0.05);第60天时,巴氏杀菌乳组血清IL-1β含量极显著高于酸化乳组(P<0.01),血清IL-6含量显著高于酸化乳组(P<0.05);第90天时,巴氏杀菌乳组血清IL-1β含量显著高于酸化乳组(P <0. 05)。综上所述,利用甲酸酸化牛乳对牛乳成分影响不大,可抑制牛乳中有害细菌生长,改善适口性,提高犊牛采食量,改善机体免疫力。     

双歧酸化乳清粉代替进口乳清粉对乳仔猪生产性能的影响

本研究选用胎次、母猪泌乳力相近、同时分娩的体重接近、健康的杜×长×大7日龄乳仔猪54头,按照随机完全区组设计,评定双歧酸化乳清粉代替进口乳清粉对断奶仔猪生产性能的影响.结果表明,双歧酸化乳清粉代替进口乳清粉显著提高了乳仔猪的日增重和料肉比,改善了断奶应激,有利于维持乳仔猪的健康和保持其良好生长性能.     

传统Raib型牛奶发酵乳中野生Leuconostocs菌和乳酸球菌的分离及鉴定

Raib(Rayeb)是由乳球菌和明串珠菌发酵产酸进而酸化和产生风味的一种自然发酵乳。Raib及其副产品是许多地中海和撒哈拉以南非洲国家的传统食品。当前尚未有用于发酵Raib的专门发酵剂。本研究目的是分离和鉴定可用于Raib及其副产品的生产,并能保持自身传统特性的天然乳球菌和明串珠菌菌株。在实验室中采用M17和MRS(含万古霉素)培养基,从新鲜阿尔及利亚牛乳、绵羊乳、山羊乳、马乳、骆驼乳等原料乳或其发酵乳中分离了优势乳酸球菌,提取这些菌株的DNA,并且采用Rep-PCR技术对上述菌株指纹图谱分析。采用Rep-PCR技术结合Enterococcus属特异性引物、Lactis/hordniae和Cremoris ofLactococcus lactis.亚属特异性引物,对菌株进行鉴定。分离获得菌株的3个与Raib生产相关的特性被确定,其中包括在正常的相关温度范围内体现的高酸化能力、蛋白酶活性及柠檬酸代谢能力。84株菌被定性,其中包括4株乳球菌和4株明串珠菌;具有抗万古霉素的肠球菌,常常被共分离。一株Leuconostoc mesenteroides菌与亚种模式菌株以及其他天然明串珠菌相比,显示了非典型的表型特征。两株分离自骆驼发酵乳,并具有蛋白酶活性的Lactococcus lactis subsp.lactis biovar diacetylactis和分离自马发酵乳的Leuconostocmesenteroides subsp.Mesenteroides在乳中显示高的酸化潜力;以上3株菌适合用作酸化发酵剂,它们既可保留传统Raib的传统的感官特性,同时可以改善Raib的安全性和延长货架期。     

分离自蒙古国发酵乳制品的保加利亚乳杆菌产酸特性及发酵乳的酸组分

以保加利亚乳杆菌生产菌株结合实验室不同分离源的库存菌株为研究对象,评价保加利亚乳杆菌后酸化过程.选取12株分离自蒙古国不同地区发酵乳制品中保加利亚乳杆菌菌株结合1株商业菌株为研究对象并发酵酸奶,在发酵完成后的低温贮藏阶段(0～48 h、7d、14d和21 d),分别测定菌株发酵酸奶所需时间、贮藏期间滴定酸度、pH值以及采用反相高效液相色谱法测定有机酸含量,综合发酵产酸特性和酸奶后发酵过程中酸组分含量变化,最终得到弱后酸化菌株IMAU20458.     

低浓度淀粉乳的酸化降解条件的实验研究

研究了低浓度淀粉乳的酸化降解条件及影响因素，结果表明，1％浓度的玉米淀粉乳在酸化酸度pH=6～8，温度35℃左右，酸化时间不小于45s时，可以使淀粉乳的黏度和淀粉的聚合度显著降低；同时，酸的种类及其他添加剂对淀粉酸解的影响很小。对淀粉乳酸化产物的IR分析表明，淀粉的酸化产物主要为聚合度较小的淀粉。     

幼畜代乳料的配制

优质幼畜代乳料能很快溶解在水中成为溶液,直至幼畜采食前仍保持稳定的质地。然而,当非乳成分及以植物为基体原料的成分增加时,就难于生成稳定的溶液。乳化剂(emulsifiers)对油或脂肪以及其他不易溶解的成分在水中混合均匀起着关键作用。乳化剂是以一种“体系”或以在乳化过程中起着一系列作用的复合物的组合态存在。乳化剂系统通常由一种乳化剂与一种稳定剂组成。代乳料中乳化剂通常是一种以脂肪或脂肪酸或山梨醇为基底的非离子表面活性物质。稳定剂是卵磷脂或者是蛋白质的复合物。适宜的乳化剂能够引起脂肪的自发乳化作用,形成细小的脂肪颗粒,而稳定剂可防止这种细小颗粒的凝集。     

Optimum use of milk in traditionally managed cattle herds in the tropics

In traditional cattle systems in the tropics, the milk produced is generally shared between the calf and the cattle keeper. This literature review evaluates the socio-economic aspects related to milk production and milk use in traditional cattle systems and identifies the best strategies of milk allocation in order to improve food security and maximise income. The available literature indicates that milk, in terms of economic, social and subsistence value, is more valuable than meat. Thus, under the conditions that characterise traditional cattle systems in the tropics, it is appropriate to have a higher milk offtake at the expense of calf growth. This review also found that certain management practices, such as restricted suckling, can be useful to minimise mortality of calves, while improving milk offtake for human consumption.     

Current aspects of the use of automated milking systems

Automatic milking systems offer not only a marked improvement of the working conditions in dairy farms but also they may be able to improve the quality of life of the dairy farmer, the health and performance status of the cow and the milk quality. The current stage of development of automatic milking systems indicates that there are still some deficiencies in fulfilling the requirements of the milk hygiene regulations, the early identification of health problems and allowing veterinary measures. This paper details some aspects of cow and udder health and milk quality under the condition of automatic milking systems by discussing actual problems and potential future advantages.     

Sensors and management support in high-technology milking

Two directions can be distinguished in the development of high-tech milking equipment: 1) high-capacity milking parlors with a high throughput of cows per person per hour and 2) automatic milking systems in which manual labor is replaced by a milking robot. High-capacity milking parlors are developed in such a way that one operator is able to milk many cows, partly by automation and partly by optimization of available labor. In such parlors, one operator can milk up to 125 cows per hour. This means that there are only a few seconds available for udder preparation. In an automatic milking system, a robot takes over all manual labor during milking. Currently available systems have one robot arm working with one milking stall (one-stall system) or one robot arm working with more milking stalls (multiple-stall systems). Cows have to go to the automatic milking system voluntarily. Therefore, there is a large variation in milking intervals. Moreover, a large variation between milkings and between cows was observed in milk flow rate, machine-on time and udder preparation time. Both developments in high-tech milking have effects on the milk ejection. The small amount of time dedicated to udder preparation in high-capacity milking parlors has negative effects on the milk ejection, among others leading to more bimodal milk flow curves and longer machine-on time. In automatic milking systems, the variation in time between udder preparation and cluster attachment and in milking frequency might have an effect on milk ejection. Lactation physiology can play a role in solving the questions around milk ejection in high-tech milking systems. The introduction of high-tech milking systems makes decision support systems using sensors necessary. These systems should assist in detection of abnormal milk and mastitis. To a lesser extent, diseased cows need to be brought to the attention of the dairy farmer. Some sensors are currently available for this purpose, but they do not fulfill all demands. In the near future other sensors might be developed. It is important that this development is demand driven and not technology driven. Lactation physiology can play an important role in the determination of milk components useful for automatic detection.     

奶牛生产风险评估指标、评估方法的确立——以湖北省黄冈市为例

利用系统工程的理论和方法对黄冈市奶牛生产进行系统分析,利用系统诊断的方法,确定奶牛生产风险的主要因素、次要因素和一般因素。通过对影响奶牛生产风险因素的分析,并根据奶牛生产风险评价指标体系建立的原则,确立黄冈市奶牛生产风险评价指标体系,依据评价标准确定的原则,提出比较适宜的黄冈市奶牛生产风险评价标准。     

淀粉与牛奶蛋白相互作用研究进展

淀粉与牛奶蛋白的共存存在于众多食品体系中。本文系统地介绍当前国内外学者对于淀粉与牛奶蛋白相互作用的研究进展,重点介绍在酸奶与奶酪体系中淀粉与蛋白之间相互作用的研究,表明淀粉与牛奶蛋白相互作用影响食品凝胶结构,进而改变食品的质构与口感,以期为变性淀粉在乳品饮料中的应用提供一定的理论依据。     

牛奶中雌激素残留检测方法研究进展

雌激素作为一种类固醇激素,因其对动物及人类内分泌系统的潜在危害已经引起了越来越多的关注.牛奶在人类日常饮食结构中占有重要位置,研究表明在如今的商业牛奶中雌激素含量呈持续上升趋势.本文阐述了牛奶中雌激素的来源及危害,并重点介绍了对其残留检测方法的研究进展.     

Supplementation with bypass fat in silvopastoral systems diminishes the ratio of milk saturated/unsaturated fatty acids

This study was conducted to evaluate if supplementing bypass fat to cows under silvopastoral systems, increases the concentration of unsaturated fatty acids in milk, thus improving the saturated/unsaturated ratio without a negative effect on total milk yield in fat or protein. Two concentrations of two different sources of bypass fat were evaluated for 40 days, each in a group of 24 multiparous Lucerna (Colombian breed) cows. A cross-over design of 8 Latin squares 3 × 3.was used The variables submitted to analysis were body condition, daily milk production and milk composition. Body condition, milk yield and milk quality were not different but there was a significant decrease in the amount of saturated fatty acid in both experiments while the unsaturated fat increased significantly in experiment 1 and remained stable in experiment 2. Results, such as these have as far as we know, not been reported previously and they provide an approach for the improvement of milk as a “functional food”.     

Ostertagia ostertagi antibodies in milk samples: Relationships with herd management and milk production parameters in two Mediterranean production systems of Spain

The present study analyzed Ostertagia ostertagi antibodies by indirect ELISA in milk samples in two cattle systems in Mediterranean Spain to indirectly monitor gastrointestinal nematode (GI) parasitism effects on production. Individual samples from 10 animals and the corresponding milk herd samples were collected from 133 herds in Girona (intensive management) and 123 herds in Minorca (extensive management). Both locations showed high and significant positive relationships between average optical density ratios (ODR) of individual animals and ODR in their milk tank. Although antibodies levels were low, there were significantly higher in Minorca. Negative correlations between ODR values and milk production were found in both systems. Importantly, in Minorca, average herd milk production was higher in the herds that treated their animals against GI nematodes compared to those that did not treat. The ELISA technique was valuable to indirectly assess differences in the level of GI nematode infection even in cattle production systems with low levels of infection.     

The effect of a single prolonged milking interval on inflammatory parameters, milk composition and yield in dairy cows

A technical stop in automatic milking systems may result in a severely prolonged milking interval (PMI) with subsequent impact on milk somatic cell count (SCC). This study investigated the inflammatory reaction, milk composition and yield during SCC peak observed in composite milk after exposing cows to a single PMI of 24h. At the first milking after the PMI, a sharply increased proportion of milk polymorphonuclear leukocytes (PMN) but marginally increased SCC were observed. The peak in SCC was not seen until morning milking day 2 after the PMI, notably, concomitantly with a decreased PMN proportion. An increase in blood lactose, milk bovine serum albumin and serum amyloid A (SAA) and a drop in milk alpha lactalbumin (ALA) were seen concomitantly with the peak in PMN. All parameters mentioned, had returned to base line after day 2. The changes in SCC and SAA had the longest duration. Lactate dehydrogenase in afternoon milk was decreased during the whole study as was also afternoon milk yield. Interleukin-1β could not be detected in milk at any time. SAA and ALA, respectively, may influence chemotaxis and the changed concentrations observed after the PMI might have contributed to the increased migration of PMN to milk.