The use of transglutaminase in dairy products

Modification of proteins by enzymes such as transglutaminase (TG) has recently become of great interest to food scientists. TG (EC 2.3.2.13) catalyses the post-translational modification of proteins by transamidation of available glutamine residues by the formation of covalent cross-links between glutamine and lysine residues in proteins. It is suggested that TG is a useful tool for the production of dairy products. In this review, properties of TG and its possible use in the manufacture of dairy products are discussed. Aspects covered include reactions catalysed by the enzyme and properties of modified proteins of selected milk proteins and products.     

光谱技术在乳及乳制品研究中的应用进展

文章阐述了光谱技术在乳及乳制品掺假和掺伪检测、营养成分检测、抗生素检测、微生物污染检测,乳及乳制品种类的鉴定等方面的应用。综述了近红外光谱、拉曼光谱、高光谱成像技术在乳及乳制品品质检测和安全评定上的重要应用和研究进展,指出多种技术联合应用是未来研究的趋势。     

Calcium in dairy products

Increasing attention has been given to the nutritional role of calcium because many Americans do not consume their Recommended Dietary Allowance of this nutrient and because calcium deficiency may lead to the development of osteoporosis or other disorders. Calcium is absorbed in the intestines with the aid of a vitamin D metabolite and is used in the body for many essential functions. There are several ways to obtain calcium in the diet, but the best sources are milk and other dairy products because of their low cost and high bioavailability of this mineral. Some manufacturers have responded to the concern over lack of calcium in the diet by increasing its levels in milk. The amount of calcium in cheese and yogurt also can be elevated.     

Mycotoxins in dairy products

Certain fungi produce chemical substances that cause toxic symptoms when food containing them is ingested by man or animals. These compounds are referred to as mycotoxins. Mycotoxins may contaminate dairy products by moulds growing on them, or by the carry-over of mycotoxins occurring in animal feedstuffs ingested by dairy cattle. An example of the first mentioned category is sterigmatocystin, a carcinogenic mycotoxin sometimes occurring on hard cheese. An example of the second category is aflatoxin M₁, a compound strongly suspected to be carcinogenic, which often occurs in milk. Due to the fact that processing of milk does not decrease the aflatoxin M₁ content, aflatoxin M₁ occurs in various dairy products. Sensitive methods of analysis for the determination of mycotoxins in dairy products have been developed in the last 10 years, most of them are based on TLC- or HPLC-separation procedures, followed by fluorimetric measurement.The most fundamental way to tackle the problem of mycotoxin contamination of dairy products is to prevent fungal growth on the dairy products or, in the case of carry-over of mycotoxins, in the crop before, during and after harvest. If measures to prevent fungal growth and mycotoxins production are not taken or fail, one can sometimes resort to physical or chemical methods to eliminate mycotoxins.     

Evaluation of the possible use of potentially probiotic Lactobacillus strains in dairy products

In the study, the ability of two potentially probiotic strains Lactobacillus plantarum 14 and Lactobacillus fermentum 4a to milk fermentation and the possibility to use them in yogurt production were investigated. The strains did not acidify milk during 24 h and 72 h fermentation at 37C, but grew well and remained at the level of 10⁸ colony-forming units (CFU)/mL during 21 days of cold storage. Their application to yogurt production along with commercial starter culture consisted on L. delbrueckii ssp. bulgaricus and S. thermophilus allowed to obtain products with typical sensory properties, pH values and numbers of potentially probiotic bacteria at desired level 10⁷ CFU/mL.     

奶制品中的乳化剂和胶凝剂

<正> 乳品工业在世界范围的产品种类是多种多样的,这些产品根据其外观、物理特性或生产工艺来进行分类。 乳制品通常分为以下几类:液体、发酵、浓缩的、胶凝的、冰冻的、干燥的等等;这几大类又可分为许多亚类。就所涉及的乳化剂/水溶胶而言,可应用的亚类是很多的,因为一般产品都具有常见特     

Phospholipids in milk and dairy products

A rapid HPLC method has been developed for the analysis of the phospholipids in milk and dairy products. A concentrate of the phospholipids was obtained by chromatography on a cartridge of silica gel. The relative proportions of the different phospholipids were then determined by HPLC, and by means of the addition of an internal standard, dipalmitoyl phosphatidyldimethylethanolamine, the absolute amounts present were also measured. After the reproducibility of the method was demonstrated with fresh whole milk, it was applied to skimmed milk, buttermilk and various products of ultra-high temperature processing. Small differences only were seen in the relative compositions of phospholipids in different milk products, but the absolute amounts varied appreciably. In some samples, it was tentatively concluded that the phospholipids had undergone extensive autoxidation.     

功能性乳制品

<正> 随着生活水平的提高,人们的保健意识愈来愈强,具有功能性的乳制品正逐渐成为崇尚健康的消费者的选择。来自芬兰的维利奥(Valio)有限公司在功能性乳制品研发方面取得不断的创新。     

Production of novel dairy products using actinidin and high pressure as enzyme activity regulator

Milk clotting for the production of novel dairy products, alternative or complementary to cheese and yogurt type products can be achieved using plant sulfhydryl proteases. The objective was to apply the protease actinidin, from Actinidia chinensis, as the milk clotting agent, and High pressure (HP) technology to control excessive proteolysis. The effect of the dairy substrate and the process parameters on the coagulation rate and the texture and sensory properties of the end product, were studied. Selected values of design parameters were 25% total solids, 6.49 adjusted pH, 0.35 U activity of the clotting agent actinidin, 40 ºC process temperature and 2 h time. The selected pressure-temperature conditions, 600 MPa at 40 ºC, were applied to stop the potentially detrimental further proteolytic action of the enzyme. Results indicated that use of actinidin for milk clotting and HP to stop the enzyme activity in the final product, leads to a “fresh cheese” type dairy product.Industrial relevance: Alternative clotting methods for novel dairy products, complementary to cheese and yogurt type products, are of interest to the industry. Plant proteases can be a viable approach, provided that excessive proteolysis after structure formation is regulated. High hydrostatic pressure can be used for controlling proteolytic activity in the final products without affecting their texture and sensory characteristics.     

The shelf-life of dairy products: 4. Intermediate and long life dairy products

In the fourth and final part of this series of broad reviews, the factors controlling the shelf-life of selected intermediate and long life dairy products are discussed. Although the extent of contamination of the raw material by psychrotrophic bacteria is relevant, in contrast to short shelf-life products microbial contamination is of secondary importance to chemical change. Lipid oxidation, Maillard reaction and calcium induced aggregation may all limit shelf-life. Examples of susceptible dairy products have been chosen and methods for extending shelf-life are discussed. It is clear that no common strategy exists and optimization of shelf-life must be carried out on a product by product basis.     

Bioactive peptides in dairy products

Bioactive peptides are hydrolysates with specific amino acid sequences that exert a positive physiological influence on the body. They are inert within the native protein, but once cleaved from the native protein by microbial or added enzymes and/or gastrointestinal enzymes during the digestive process, they apply their beneficial traits. Dairy products, particularly fermented products, are potential sources of bioactive peptides: several of them possess extra‐nutritional physiological functions that qualify them to be classified under the ‘Functional Foods’ label. Biological peptides in milk, the methods of their generation and their prevalence in dairy products are reviewed along with the reported health benefits and safety aspects.     

Sphingoid bases in dairy products

Sphingolipids have recently been taken more into consideration because of their possible role in health care.The aim of this study was to determine the concentration of free and total sphingosine and sphinganine in dairy products, a food group that has been given a role in the prevention of colon cancer and other tumours. Sphingolipids were extracted using chloroform and methanol, and following base and acid hydrolysis, the free and total sphingosine and sphinganine were quantified using high-performance liquid chromatography. The highest concentrations of free and total sphingosine and sphinganine were found in sour cream. In most of the analyzed dairy products, the concentrations of free sphingoid bases were lower than that of cow’s milk, while the concentrations of the total sphingoid bases were equal to or higher than that of cow’s milk.     

Biogenic amines in dairy products

Biogenic amines (BA) are organic, basic, nitrogenous compounds with biological activity, mainly formed by the decarboxylation of amino acids. BA are present in a wide range of foods, including dairy products, and can accumulate in high concentrations. In some cheeses more than 1000 mg of BA have been detected per kilogram of cheese. The consumption of food containing large amounts of these amines can have toxicological consequences. Although there is no specific legislation regarding the BA content in dairy products, it is generally assumed that they should not be allowed to accumulate. Greater knowledge of the factors involved in the synthesis and accumulation of BA should lead to a reduction in their incidence in foods. This article focuses on the factors that affect BA production, in particular environmental conditions, the microorganisms that produce them, the genetic organization and regulation of the biosynthetic pathways involved, and the available methods for detecting the presence of BA or BA-producing microorganisms in dairy products.     

乳制品中纳他霉素的测定

建立了测定乳制品中纳他霉素含量的高效液相色谱法。样品用甲醇萃取后进样,采用Thermo ODS-2250min&#215;4.6mm色谱柱分离,流动相为乙酸铵与氯化铵的缓冲液：乙腈=4：1（体积比）,加入5InL四氢呋喃（每升）,紫外检测;A-R303nm,RSD为0．56％-0．82％（n=5）,标准曲线r=0．9998,平均回收率分别为98．2％,最低检出限为0．05mg／L。本法具有操作简单、灵敏度高和准确性好等优点。     

卵磷脂在乳制品中的应用

<正> 卵磷脂萃取自大豆,是一种天然的乳化剂,可广泛应用于不同的食品中。在乳制品中,卵磷脂已普遍在奶粉、干酪、冰淇淋和奶油制品等产品中使用,本文将详细探讨这些领域的应用情况。 速溶奶粉 奶粉通常采用附聚处理以形成粗糙的颗粒,便于冲调饮用。然而,由于奶粉颗粒大多被脂肪覆盖,形成对水的排斥性,故此,单独采用附聚处理,不能     

亲水性胶体在乳制品工业中的应用

<正> 亲水性胶体是指水溶性多糖,其作用是使多糖分散体系具有黏度和形成凝胶的能力。根据原料来源,亲水性胶体可分为:生物胶(黄原胶、葡聚糖、结冷胶)、植物胶(刺槐豆胶、瓜尔豆胶)、植物渗出液(阿拉伯胶、黄耆胶)、海藻胶(卡拉胶、琼胶)、纤维素及衍生物(纤维素、羧甲基纤维素(钠))、淀粉及其衍生物、动物胶(明胶)、果胶。 在乳制品工业中被广泛应用的亲水性胶体主要有刺槐豆胶、瓜尔豆胶、果胶和卡拉胶。主要作用是保护体系中的蛋白质以耐受加工中     

Enumeration of bifidobacteria in dairy products

There is much interest in the potential role of bifidobacteria as dietary inclusions, but their isolation from dairy products, and subsequent identification, can cause problems. A range of selective and non-selective media were examined, and modified Rogosa agar was found to give the best recovery from yogurt-like products. A morphological examination of typical isolates suggested that only bifidobacteria had grown on the medium, but confirmation by means of biochemical tests proved inconclusive, and it seems that the genus/species definition merits further attention.