我国干酪凝乳酶研究及应用现状

近年来,随着干酪产量的增加,从小牛皱胃中提取的皱胃酶产量已经不能满足干酪生产的需要,迫使人们不得不寻找其它凝乳酶来代替小牛皱胃酶,因此凝乳酶的研究显得愈来愈重要。本文对目前的凝乳酶进行综述,重点论述了动物凝乳酶、植物凝乳酶、微生物凝乳酶以及遗传工程凝乳酶的研究及应用现状,为解决凝乳酶的短缺问题提供思路。     

干酪凝乳酶代用品研究

针对干酪凝乳酶供应短缺，为寻找凝乳酶的最适代用品，采用L16（4^5）正交实验设计，研究加入不同水平的小牛皱胃酶、乳猪胃酶、育肥猪胃酶对干酪生产的影响，结果表明：乳猪胃酶能以50－66．7％的比例替代小牛皱胃酶，育肥猪胃酶不能用来替代。三种凝乳酶对干酪特性好坏影响的排序是小牛皱胃酶＞乳猪胃酶＞育肥猪胃酶。     

国内凝乳酶及其代替品的研发进展

凝乳酶是干酪制作过程中起凝乳作用的关键性酶,它对干酪的质构和特有风味的形成有影响。本文阐述了干酪生产的现状,凝乳酶的结构和凝乳杌理,凝乳酶活性的影响因素,并介绍了国内凝乳酶代替品的研发进展。     

酸-酶共促凝乳的研究进展

本文针对夸克干酪、农家干酪等新鲜干酪的酸-酶共促凝乳方式,在概述酶凝、酸凝的基础之上,论述了酸-酶共促凝乳的形成过程及性质,并探讨了凝乳酶浓度、热处理、添加凝乳酶时pH值等对酸-酶共促凝乳的影响。     

Mozzarella干酪与模拟干酪成熟过程中菌群及pH的变化

干酪凝块中含多种微生物和酶，这些微生物和酶在没有采用有效防治措施的条件下易发生作用，可发生生物、生化和化学变化。通过制作正常干酪（即加乳酸菌、凝乳酶）、两份模拟干酪（一份不加乳酸菌改用盐酸直接酸化、另一份不加凝乳酶改加葡萄糖酸内酯将乳凝结），再将其进行对比，研究菌群在成熟过程中的变化，结合蛋白水解、风味变化、微观结构，以找出菌群在干酪成熟中的确切作用。     

新鲜软质豆乳干酪的研制

以豆乳替代部分牛乳制作新鲜软质豆乳干酪,采用单因素试验方法,研究豆乳添加量、CaCl2和凝乳酶对凝乳时间和感官的影响;并用正交试验确定了生产新鲜软质豆奶干酪的最佳配方.结果表明,当豆乳添加量20％、CaCl2添加量0.04％、凝乳酶添加量0.02％时制备的产品品质最佳.     

地衣芽孢杆菌D3.11凝乳酶对切达干酪质地特性的影响

为揭示地衣芽孢杆菌D3.11凝乳酶对切达干酪成熟过程中质地的影响,利用地衣芽孢杆菌D3.11凝乳酶制作切达干酪(CDF组)和切达干酪类似物(CD3组),采用商品凝乳酶作为对照(CCF组),分析干酪成熟过程中质构、流变特性、微观结构的变化规律.结果表明:3组干酪的硬度随着干酪的成熟而增加,而弹性和咀嚼性则呈现下降趋势,C...     

切达干酪加工工艺研究

以鲜牛乳为原料,通过单因素实验和正交实验对切达干酪的加工工艺进行了初步研究,分析了凝乳酶添加量、发酵酸度、氯化钙添加量对切达干酪品质出品率的影响。结果表明,当凝乳酶添加量为7250SU,原料乳酸度为260T,氯化钙添加量为0.02%时可得到较佳的效果。     

不同因素对羊奶干酪出品率和感官品质的影响

为提高羊奶干酪的出品率和感官品质,以关中奶山羊奶为原料,研究了原料乳浓度、凝乳酶、杀菌条件、酸化条件和氯化钙对羊奶干酪出品率和感官品质的影响。结果表明,原料乳浓度较高,凝乳酶选用羔羊凝乳酶,杀菌条件63℃,30min,酸化pH6.4,氯化钙添加量0.01%-0.02%时干酪出品率较高、感官品质较好。     

脂肪含量对再制片状干酪品质的影响

研究不同脂肪含量和脂肪替代物对再制片状干酪品质的影响。对5 种不同脂肪含量再制片状干酪的基本理化指标、色泽、质构和感官品质进行测定和评估。结果表明：5 种不同脂肪含量的再制片状干酪pH值、蛋白质和脂肪含量存在显著性差异,酶解浓缩黄油的添加对再制片状干酪亮度值、红度值和黄度值均有明显影响;用酶解浓缩黄油替代全部黄油的减脂50%干酪全质构特性与其他组样品有差异,酶解浓缩黄油部分替代黄油制备的4号减脂干酪全质构特性除凝聚性、回复性外,与1～3号干酪无显著差异;通过感官评定发现,酶解浓缩黄油替代全部黄油的减脂50%干酪（5号）感官评分最低,酶解浓缩黄油部分替代黄油的减脂50%干酪（4号）风味和滋味有所增强,总体得分与全脂干酪产品无显著差异。因此通过降低黄油含量,并添加酶解浓缩黄油可提升减脂再制片状干酪的品质。     

The evaluation of the curd forming ability of milk replacers

Inadequate milk curd formation in the abomasum of newborn calves causes malnutrition and diarrhea. In order to define the factors of inadequate curd formation, we compared the curd forming ability among 9 kinds of milk replacers, bulk milk (raw milk), and skim milk both in vitro and in vivo . When rennet was added, the raw milk and one milk replacer formed firm curds. The rest of the milk replacers and skim milk did not form any curd. When a solution of HCl was added, raw milk, three milk replacers and skim milk formed the curd at pH 4.5, but the other milk replacers did not. When HCl was added following the rennet, raw milk, one milk replacer and skim milk formed the curd. In vivo , raw milk, two milk replacers and skim milk showed good curd formation whereas the other milk replacers showed poor curd formation inside the abomasums of the calves. This study showed that most of the milk replacers sold in Japan could not form the curd with rennet.     

Effect of enhancing curd formation during the first colostrum feed on absorption of gamma glutamyl transferase by newborn calves

OBJECTIVE: To examine the effects of curd formation within the abomasum, on the absorption of gamma glutamyl transferase (GGT) from colostrum in newborn calves. DESIGN: An in vivo physiological study with controls, and in vitro examination of calf abomasal fluid. PROCEDURES: Newborn calves were taken from cows without allowing them to suckle. They were fed either 1.5 kg colostrum or 1.5 kg colostrum plus rennet, with intervals between calving and colostrum feeding ranging from 0.4 to 12.7 h. Absorption of proteins from the whey component of colostrum was assessed from the rise in activity of serum GGT. In in vitro studies, colostrum was incubated with bovine amniotic fluid, newborn calf abomasal fluid or newborn calf forestomach contents, with or without rennet, to test the curd inhibiting effects of components in the abomasal fluid of newborn calves. RESULTS: In vivo: addition of rennet to the colostrum feed reduced the proportion of calves with serum GGT activity below 500 U/L by 60%. In vitro: 43% of newborn calves lacked curd forming activity in their abomasal fluid, and that deficiency was corrected by adding rennet to the incubation medium. CONCLUSIONS: Some calves are born with low amounts of curd forming enzyme activity in the abomasum. This may compromise their ability to absorb large whey proteins from the first feed of colostrum. Adding rennet to the first colostrum feed may improve passive immunity in those calves.     

The effect of frequent milk feeding on abomasal curd formation of Holstein calves

In order to understand the effects of the automatic milk replacer feeding system on calf health, we examined the effect of frequent milk feeding on curd formation in the abomasum using ultrasonographic imaging. Eight male Holstein calves were divided into a milk-replacer group and a fresh milk group. Calves were fed twice a day to 12 days after birth (Period A). From 13 days, calves were fed six times a day (Period B). The abomasal fluid was taken by paracentesis. In both periods A and B, the fresh milk group formed bigger curds faster than the milk replacer group. The curd score of the milk replacer group in period B at 2 h was significant lower than those of both groups in period A. The pH in the abomasum was lower in period B than in period A. We could not identify the location of the abomasum in the milk replacer group during period B at almost time points. Our experiment suggests the possibility that frequent feeding of milk replacer causes incomplete hydrolysis of κ-casein as well as curd formation, thus reducing the digestibility compared to the feeding of the milk replacer twice per day or frequent feeding of fresh milk.     

简析凝乳酶凝乳机理及羔羊凝乳酶自制方法

本文重点介绍了凝乳酶的种类和凝乳机理,以及自制羔羊凝乳酶及其活力测定的方法,对引导我国家庭牧场和小型羊乳企业突破凝乳酶自制核心技术,创新开展羊奶酪生产研发,填补国产羊奶酪市场空白与丰富羊乳制品种类,具有重要的指导意义。     

Vitamin E serum levels in calves after various methods of administration]

We observed the levels of vitamin E in the blood serum of calves after peroral application of Combinal E (1 ml contains 20 mg of tocopherol acetate in water solution), after application through a fistula into the rennet stomach and after an intramuscular injection of Erevit (1 ml contains 300 mg of tocopherol acetate in vegetable oil). The fastest increase in the vitamin E level was recorded after the application of Combinal E directly into the rennet stomach. The application of Combinal E per os resulted in the same level of vitamin E in the ninth hour after application as in the third hour after application into the rennet stomach, the intramuscular injection of Erevit had a much lower effect on raising the vitamin E level in the blood serum of calves. It was confirmed that for a faster supplementing of vitamin E to the organism it is more suitable to give Combinal E perorally.     

Streptococcus phocae infections associated with starvation in Cape fur seals

Mortalities and abortions associated with starvation occurred at Cape Cross, Namibia, in Cape fur seals (Arctocephalus pusillus pusillus). Affected seals showed lethargy and emaciation, and the most common pathological signs were those of a respiratory infection, both in adults and offspring. Streptococcus phocae was isolated from adult seals, a cub and aborted foetuses.     

Transmission of a Trypanosoma sp. to cattle by the tick Hyalomma anatolicum anatolicum

Hyalomma anatolicum anatolicum engorged nymphs and flat adults were collected from two areas in northern Sudan. Various developing stages of Trypanosoma theileri-like flagellates were observed in the engorged nymphs, freshly moulted adults and mature adults partially engorged on rabbits. When these ticks were applied to two calves, one calf became infected with the trypanosome. The parasites were observed for one day in the enlarged lymph node nearest to the tick-feeding site 5 days after the tick application. Subsequently the trypanosomes were re-isolated in vitro from the infected calf. Inoculation of a ground-up tick supernatant suspension from the infected batch of ticks containing 10(4) trypanosomes into a calf did not produce a patent infection.     

Inhibitory effects of organic acids and salts on selected micromycetes]

Inhibitory effects of two fungistatic preparations (A and B) and of propionic acid were tested in a complete feed mixture for broiler chickens (starter mixture). The water content of this mixture was 25.4%, environmental temperature was 24 degrees C and relative air humidity 90%. Propionic acid, which has a high fungistatic effect, served as a standard. The composition of the preparation A was as follows: propionic acid, acetic acid, sorbic acid, citric acid and calcium propionate. The preparation B contained: sorbic acid, citric acid and calcium propionate. Examinations were performed in a naturally contaminated and subsequently sterilized (25 kGy) feed mixture; it was then infected with Aspergillus fumigatus, A. niger, A. parasiticus and Penicillium purpurogenum from the Collection of Animal Pathogenic Microorganisms, Brno. A. flavus, A. fumigatus, A. glaucus, Penicillium sp., Absidia corymbifera, Mucor sp., Rhizomucor pusillus were detected in the naturally contaminated feed mixture. The mycoflora which was found in the native substrate was resistant to both tested fungistatic preparations; and this resulted in mycelium growth from 7th day of incubation. The efficiency of the preparations A,B and of propionic acid in the feed mixture was identical at concentrations of 4 mg/kg, 7 mg/kg and 3 mg/kg, respectively, and their inhibitory effects were lowest at these concentrations (Fig. 2). A high water content in the nutrient substrate resulted in the rapid growth of fungi of the Mucorales species. The relative humidity of the environment (90%) and water content of tested samples affected markedly micromycetes growth in this experiment.(ABSTRACT TRUNCATED AT 250 WORDS)