凝乳酶的发展及其在奶酪生产中的应用

随着我国乳制品行业的快速发展,奶酪的生产越来越受到人们的关注.凝乳酶是在奶酪生产过程中起凝乳作用的关键性酶,势必将成为我国未来重点开发的酶制剂之一.本文通过简要介绍凝乳酶的种类、结构、一般特性、凝乳机理以及不同凝乳酶在奶酪生产中的应用,综述了凝乳酶的研究进展,对凝乳酶的开发前景进行展望.     

乳品科普知识——奶酪荟萃

<正>名词释义:1奶酪:奶酪又名干酪、芝士或乳酪(英文名Cheese),是乳凝聚后的浓缩产品,含有丰富的蛋白质、脂肪、钙、磷和维生素,味道独特,易运输保存,有较长的货架期。奶酪是种类最多的乳制品,全世界奶酪种类有800多种。2鲜奶酪:鲜奶酪是鲜奶经发酵剂发酵或凝乳酶凝乳之后,排除乳清得到的产品,不经过成熟,质地细腻,色泽洁白,吃起来有淡淡的咸味和清新的乳香     

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。     

不同凝乳酶对干酪凝乳性能的影响

以小牛皱胃酶、木瓜凝乳酶和微小毛霉凝乳酶作为动物、植物和微生物凝乳酶进行干酪凝乳实验,研究不同类型凝乳酶对干酪品质的影响,并进行用部分非动物凝乳酶来替代动物性凝乳酶实验。结果表明：小牛皱胃酶制作的干酪品质最佳,木瓜蛋白酶对制作干酪的品质影响较大,而用添加量小于25%的微小毛霉凝乳酶来替代部分小牛皱胃酶,且此替代量不会造成大的干酪风味和口感的缺陷。     

植物凝乳酶凝乳特性的研究

从凝乳酶的最适作用温度，酶的热稳定性，ｐＨ对植物凝乳酶活性的影响，植物凝乳酶对ｐＨ的稳定性，Ｃａ＾２＋对植物凝乳酶活性的影响，以及底物浓度对植物凝乳酶凝乳活性的影响等方面深入阐述植物凝乳酶乳特性，并分别进行了讨论。     

凝乳酶在干酪生产中的应用

本文在概述凝乳酶及其在干酪生产中作用的基础之上,论述了目前凝乳酶供不应求的现状与有关新来源凝乳酶的研究进展,并探讨了凝乳酶在干酪中应用的新趋势。     

羊奶奶酪制作核心技术的初步研究

[目的]本研究以羊乳为原料，结合奶酪工艺初步探讨了羊奶酪的主要技术参数。[方法]通过对羊奶的杀菌温度、发酵剂添加量、CaCl₂添加量、凝乳酶添加量等因素进行正交试验，以产品质构、综合感官评价为指标，得到最佳用量配比。[结果]羊奶奶酪的最佳工艺为：杀菌条件75~78 ℃，15 s，发酵剂添加量为1.4 %，CaCl₂的添加量为0.03%，凝乳酶添加量为0.01%，在传统奶酪制作工艺的基础上以此技术参数生产的羊奶奶酪口感、风味良好。[结论]本研究为完整羊奶奶酪技术的开发加工奠定了基础，为探寻适合中国羊乳原料及口味要求的羊奶奶酪工业化生产提供了技术依据。     

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。     

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。     

Feta奶酪生产工艺研究

本文以鲜乳为主要原料，根据Feta奶酪的生产工艺，采用L9（3^4）正交试验的方法，研究了不同发酵温度、发酵剂添加量、凝乳酶添加量、凝乳温度对Feta奶酪色泽、滋气味和组织状态的影响，确定了生产Feta奶酪的最佳工艺条件为：凝乳酶添加量1．2％。，发酵剂添加量1．0％，凝乳温度38℃。发酵温度33℃。     

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。     

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。     

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.     

牦牛乳生产Mozzarella奶酪的技术研究

以牦牛乳为原料,研究了Mozzarella奶酪的制作技术,采用四巴素三水平正交试验的方法,研究了不同量的凝乳酶、氯化钙、食盐以及发酵温度对Mozzarella奶酪成品的口感、色泽、质地的影响,确定了该产品生产的最佳生产条件。     

混合果肉羊乳扣碗酪的加工工艺研究

研制全新的具有民族特色并且适合大多数人口味的奶酪食品。采用单因素多水平试验及正交试验方法,研究出混合果肉羊乳扣碗酪的加工工艺。为:白砂糖、琼脂熬汁→过滤→杀菌→添加到过滤杀菌的羊奶中调配→冷却→加江米酒→分装→冷凝→纯化→成品。产品配方为:新鲜山羊奶400g,8%桃果肉,8%梨果肉,9%葡萄干,果肉用30%的砂糖液煮制8min最佳,7.5%白砂糖,0.5%琼脂以及1.5%江米酒。该果肉扣碗酪具有水果的保健功效,营养全面,丰富我国的乳品市场和促进羊奶产业的发展。     

Isolation of Listeria monocytogenes from Goat Cheese Associated with a Case of Listeriosis in Goat

Listeria monocytogenes was isolated from the brain of a goat, which was euthanized due to listeriosis. A few weeks later a similar subtype of L. monocytogenes was isolated from an on-farm manufactured fresh cheese which did not contain any milk from the goat which had suffered from listeriosis. A similar subtype was also found on 1 of the shelves in the refrigerator where cheeses were stored. Prior to the onset of listeriosis, 1 fresh cheese had been made of milk from the actual goat, which may have excreted L. monocytogenes in her milk. Thus, the cheese made of this milk may have contaminated the shelves in the refrigerator which then has served as a Listeria reservoir for new cheeses during several weeks.     

A multiple-phenotype imputation procedure as a method for prediction of cheese-making efficiency in Spanish Assaf sheep

Sheep milk is mainly intended to manufacture a wide variety of high-quality cheeses. The ovine cheese industry would benefit from an improvement, through genetic selection, of traits related to the milk coagulation properties (MCPs) and cheese yield-related traits, broadly denoted as “cheese-making traits.” Considering that routine measurements of these traits needed for genetic selection are expensive and time-consuming, this study aimed to evaluate the accuracy of a cheese-making phenotype imputation method based on the information from official milk control records combined with the pH of the milk. For this study, we analyzed records of milk production traits, milk composition traits, and measurements of cheese-making traits available from a total of 1,145 dairy ewes of the Spanish Assaf sheep breed. Cheese-making traits included five related to the MCPs and two cheese yield-related traits. The milk and cheese-making phenotypes were adjusted for significant effects based on a general linear model. The adjusted phenotypes were used to define a multiple-phenotype imputation procedure for the cheese-making traits based on multivariate normality and Markov chain Monte Carlo sampling. Five of the seven cheese-making traits considered in this study achieved a prediction accuracy of 0.60 computed as the correlation between the adjusted phenotypes and the imputed phenotypes. Particularly the logarithm of curd-firming time since rennet addition (logK₂₀) (0.68), which has been previously suggested as a potential candidate trait to improve the cheese ability in this breed, and the logarithm of the ratio between the rennet clotting time and the curd firmness at 60 min (logRCT/A60) (0.65), which has been defined by other studies as an indicator trait of milk coagulation efficiency. This study represents a first step toward the possible use of the phenotype imputation of cheese-making traits to develop a practical methodology for the dairy sheep industry to impute cheese-making traits only based on the analysis of a milk sample without the need of pedigree information. This information could be also used in future planning of specific breeding programs considering the importance of the cheese-making efficiency in dairy sheep and highlights the potential of phenotype imputation to leverage sample size on expensive, hard-to-measure phenotypes.     

Closantel plasma and milk disposition in dairy goats: assessment of drug residues in cheese and ricotta

Closantel (CLS) is currently used in programs for the strategic control of gastrointestinal nematodes. CLS is extralabel used in different dairy goat production systems. From available data in dairy cows, it can be concluded that residues of CLS persist in milk. The current work evaluated the concentration profiles of CLS in plasma and milk from lactating orally treated dairy goats to assess the residues pattern in dairy products such as cheese and ricotta. Six (6) female Saanen dairy goats were treated orally with CLS administered at 10 mg/kg. Blood and milk samples were collected between 0 and 36 days post‐treatment. The whole milk production was collected at 1, 4, 7, and 10 days post‐treatment to produce soft cheese and ricotta. CLS concentrations in plasma, milk, cheese, whey, and ricotta were determined by HPLC. The concentrations of CLS measured in plasma were higher than those measured in milk at all sampling times. However, the calculated withdrawal time for CLS in milk was between 39 and 43 days postadministration to dairy goats. CLS residual concentrations in cheese (between 0.93 and 1.8 μg/g) were higher than those measured in the milk used for its production. CLS concentrations in ricotta were sixfold higher than those in the milk and 20‐fold higher than those in the whey used for its production. The persistent and high residual concentrations of CLS in the milk and in the cheese and ricotta should be seriously considered before issuing any recommendation on the extralabel use of CLS in dairy goat farms.     

Survival of Listeria monocytogenes in cheese made of unpasteurized goat milk

Food-born infections with Listeria monocytogenes have been reported during recent years, cheese being mentioned as one of the foods responsible. A classical opinion is that cheese represents a very inhospitable environment for pathogens due to antagonism by the starter culture of lactic-acid-producing organisms. In order to study the survival of L. monocytogenes in goat cheese, cheeses were made with the addition of L. monocytogenes cultures. The maximum survival time for L. monocytogenes was 18 weeks in two of the cheeses. It is concluded that L. monocytogenes has the ability to survive in semi-soft cheese made of unpasteurized goat milk during normal curing (2–3 months).