Calcium: A comprehensive review on quantification,interaction with milk proteins and implications for processing of dairy products

Calcium (Ca) is a key micronutrient of high relevance for human nutrition that also influences the texture and taste of dairy products and their processability. In bovine milk, Ca is presented in several speciation forms, such as complexed with other milk components or free as ionic calcium while being distributed between colloidal and serum phases of milk. Partitioning of Ca between these phases is highly dynamic and influenced by factors, such as temperature, ionic strength, pH, and milk composition. Processing steps used during the manufacture of dairy products, such as preconditioning, concentration, acidification, salting, cooling, and heating, all contribute to modify Ca speciation and partition, thereby influencing product functionality, product yield, and fouling of equipment. This review aims to provide a comprehensive understanding of the influence of Ca partition on dairy products properties to support the development of kinetics models to reduce product losses and develop added-value products with improved functionality. To achieve this objective, approaches to separate milk phases, analytical approaches to determine Ca partition and speciation, the role of Ca on protein–protein interactions, and their influence on processing of dairy products are discussed.     

Enzymatic-fluorometric quantification of cholesterol in bovine milk

The present paper describes an enzymatic-fluorometric method for the determination of cholesterol in milk and other opaque matrices. The initial step of the method is to liberate chemically and physically bound cholesterol from the milk fat globule membrane by enzymatic action. The method is able to discriminate between esterified and free cholesterol in milk. The analysis is cost effective and is developed to work directly on whole, fresh milk thereby eliminating time consuming and tedious pre-treatment procedures of the sample. More than 1000 milk samples were analysed on the day of sampling. The total concentration of milk cholesterol ranged from 80 to 756μM (n=1068; mean 351μM). Milk cholesterol was significantly correlated to milk fat concentration as analysed by mid-infra red spectrometry (r=0.630; n=853) and by an enzymatic-fluorometric method (triacylglycerol) (r=0.611; n=842).     

Hormones in bovine milk and milk products: A survey

A survey of the published data on the occurrence of hormones in milk and milk products is presented. Bovine milk and colostrum contain a large number of hormones from either steroidic or peptidic origin. The main categories to which these molecules belong are gonadal (estrogens, progesterone, androgens), adrenal (glucocorticoids), pituitary (prolactin, growth hormone) and hypothalamic hormones (GRH, LH-RH, TRH). Other molecules, such as proteins related to the parathyroid hormone, insulin, somatostatin, calcitonin, bombesin, erythropoeitin and melatonin, are also of interest. The exact role of hormones in the development of the newborn is still not known, but it is believed that they may contribute to the growth of the newborn and to the development and maturation of its gastrointestinal and immune systems.     

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.     

Free fatty acids quantification in dairy products

Free fatty acids (FFA) in dairy products have experienced a resurgence of interest in recent years due to their associated health benefits, flavour potential and antimicrobial activity, as a direct cause of hydrolytic rancidity, and also because of the importance of accurate determination for quality, research and legislative purposes. Gas chromatographic analysis remains the technique of choice for FFA analysis; however, little advancements in method development have occurred over the last twenty years. The purpose of this review is to provide an overview of the methodology used to quantify FFA in dairy products by gas chromatography since its inception, to highlight some of the challenges experienced, to suggest aspects that could be improved to increase accuracy and throughput and reduce labour costs and solvent usage and to widen applications.     

高效液相色谱法同时测定乳及乳制品中防腐剂和甜味剂

建立了高效液相色谱法同时测定乳及乳制品中苯甲酸、山梨酸、安赛蜜和糖精钠的方法.通过加入适量沉淀剂除去样品中绝大部分蛋白质后,采用C18色谱柱.以甲醇-0.05mol/L磷酸二氢钾溶液为流动相,用紫外检测器于230 nm波长处检测.回收率在95.0%～103.0%,精密度(RSD)为1.70%2.03%,检出限分别为1.5,1.5,1.5,2.5 μg/g.该方法可用于乳制品中这4种添加剂的同时测定.     

SDT Spring Symposium: Organic milk and dairy products

objective evaluation of this Symposium results in the following three conclusi The organic speakers all laboured the view that this new sector is very ‘open’ in terms of helping each other and readily providing information. However, their actual contributions highlighted that they were less open with ‘outsiders’ in mainstream dairying. In turn, the organic presentations were characterized by (i) paucity of hard facts and lack of technical content, (ii) too much emphasis on the philosophy/ethos of organic production and (iii) associated feelings of superiority over mainstream or conventional agriculture. These considerations were compounded by two speakers not adequately addressing their specific topics and associated briefs. A niggling concern about the professionalism and commercialism of organic producers and processors, especially when they face the full blast of competition from the major dairy processors in due course. However, an overall assessment of this Symposium suggests that it still achieved the main objective set by the Society of providing an independent forum for the domestic organic sector to present its wares to the mainstream UK dairy industry.     

Yersinia enterocolitica in milk and dairy products

Yersinia enterocolitica was first recognized during the 1960's as an important human enteropathogen. The species as later redefined includes both pathogenic and nonpathogenic forms. Pathogenic strains that retain the virulence plasmid can be identified in several animal models and four indirect tests (calcium dependency, autoagglutination, Congo red uptake, serological detection of outer membrane antigen) and by tissue culture assay, serotype, and biotype. Y. enterocolitica and related bacteria have frequently been isolated from raw milk, but none of the isolates, with the possible exception of serotype 05,27, are recognizable as pathogens. Under normal circumstances Y. enterocolitica does not survive pasteurization. If introduced into pasteurized milk, it can grow well at refrigeration temperatures. Two outbreaks of yersiniosis have occurred that involved pasteurized milk. Pigs, which frequently carry pathogenic Y. enterocolitica in their throat, were the probable source in one of these outbreaks. The most rapid enrichment procedure available for isolation of Y. enterocolitica requires 6 d. No isolation method is available for selective isolation of pathogenic Y. enterocolitica in the presence of related bacteria common in milk and other foods.     

Natural antioxidants in milk and dairy products

Milk antioxidants, both lipophilic (conjugated linoleic acid, α‐tocopherol, β‐carotene, vitamins A and D₃, coenzyme Q₁₀, phospholipids) and hydrophilic antioxidants (proteins, peptides, vitamins, minerals and trace elements) play a key role in maintaining pro‐oxidant and antioxidant homeostasis in the human body. Lipophilic antioxidants are characterised by high thermal stability and they are active in all dairy products. Lipophilic and hydrophilic antioxidants interact in the process of deactivating reactive oxygen species and the final products of lipid peroxidation. A negative correlation between milk consumption and the incidence of diet‐dependent diseases confirms that the consumption of milk and dairy products delivers health benefits.     

Oxidised cholesterol in milk and dairy products

Cholesterol is found in animal foods. It can be oxidised in various ways and cholesterol oxidation products (COPs) are formed. Such products are often found in animal foods including dairy products. Recently published results suggest that the contents of COPs in milk and dairy products is very small and does not confirm the results of earlier studies. A higher concentration of COPs can be found only in processed dairy products exposed to harsh storage conditions where the impact of oxygen and light or oxygen and low water activity are concomitant.     

The shelf-life of dairy products: 2. Raw milk and fresh products

In the second of this series of articles, the specific factors controlling the shelf-life of raw milk, pasteurized milk and cream, cottage cheese and yogurt are considered. The shelf-life of raw milk depends on the quality of the milk ex-farm and on subsequent transport and storage conditions. Shelf-life may be enhanced by deep cooling or thermization. Post heat treatment contamination by Gram negative psychrotrophic bacteria is the major determinant of shelf-life of pasteurized products. In cultured dairy products, yeast and mould contamination is the most usual cause of spoilage.     

Determination of bovine lactoferrin in lactoferrin-supplemented dairy products and raw milk by an automated latex assay

Latex immune agglutination method with a multipurpose auto-analyser (the automated latex assay) was validated for determination of bovine lactoferrin (BLF) in various dairy products. Reproducibility-within-laboratory (intermediate precision) due to day for infant formula, UHT milk and yogurt supplemented with BLF at 50 mg/100 g for infant formula and UHT milk, and at 100 mg/100 g for yogurt were 1.62 to 3.10 mg/100 g. Reproducibility-within-laboratory due to analysis (morning, noon, and evening) for raw milk was 1.59 mg/100 g. Trueness, accuracy in determining known amounts added for BLF-supplemented dairy products was -4.7 to -2.0 mg/100 g. BLF concentration in raw milks was 20.3 to 21.8 mg/100 g. Although interference by the matrixes took place in infant formula and raw milk, BLF assays were accurately carried out by 2000-fold dilution or standard-addition method. Automated latex assay for BLF is simple, rapid, precise and accurate enough for a routine method in various dairy products containing BLF.     

乳品加工中超高压技术对乳品质量的影响及其应用前景分析

高静水压技术是一种重要的非热物理技术,其能耗小、无污染、效率高、对食品品质几乎无影响。因此,在食品加工中有较好的应用前景。乳及乳制品作为人们日常消费的食品,其营养物质组成丰富,也具有诸多有益的生理功能,对改善人体健康、预防疾病有重要价值。本文系统地总结了高静水压技术的特点、作用机制以及近年来在乳制品方面应用的研究状况,旨在为高静水压技术在科学研究和食品加工应用提供一定的理论参考。     

乳及乳制品中L-羟脯氨酸的测定

采用比色法对乳及乳制品中的L-羟脯氨酸质量分数进行测定.结果表明,本方法的检出限为2.1 μg/g,回收率为91.6%～101.3%.RSD为1.71%～2.45%,可用于判定乳及乳制品中是否添加动物胶原水解蛋白或者舍有游离L-羟脯氨酸.     

Proteomics of major bovine milk proteins: Novel insights

Milk proteomics covers the identification, characterisation and quantification of milk proteins. Its applications vary from the basic composition of milk proteins to their post-translational modifications (PTMs), occurring naturally or via processing and storage. Through the combination of liquid chromatography or two-dimensional gel electrophoresis with advanced mass spectrometry, milk proteomics has revealed PTMs that affect milk protein structural and functional properties. This review discusses detection by proteomics-based methods with special emphasis on natural and process induced PTMs in the major bovine milk proteins. The review covers the importance of milk proteomics in determining PTMs, especially those formed by heat treatment and during storage, and highlights some breakthroughs in PTM studies. Furthermore, aspects and applications of quantitative proteomics on milk proteins and bioinformatics are covered.     

Cold plasma processing of milk and dairy products

BackgroundThermal pasteurization and sterilization are predominantly used in the dairy industry due to their efficacy in improving the product safety and shelf life. However, heat treatment can cause undesirable protein denaturation, non-enzymatic browning, loss of vitamins and volatile flavor compounds, freezing point depression, and flavour changes. Cold plasma is a non-thermal technology that has gained attention in recent years as a potential alternative method for chemical and thermal disinfection in foods using ambient or moderate temperatures and short treatment times.Scope and approachThis review aims to describe the fundamentals, parameters, and technology on cold plasma, discussing the critical processing factors involved in this technology. Also, it describes the mechanisms of microbial inactivation and provides an overview of the effects of non-thermal plasma on the quality of dairy products, considering a physicochemical, sensory and microbiology perspective.Key findings and conclusionsCold plasma uses less aggressive mechanisms of action to the milk matrix when compared to the techniques currently used, and has shown an excellent performance on the elimination of pathogenic and spoilage microorganisms besides maintaining, in many cases, the nutritional, functional, and sensory characteristics of the product.     

Polycyclic aromatic hydrocarbons in milk and dairy products

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds with a structure consisting of carbon and hydrogen atoms that have more than two fused aromatic rings. Most PAHs have carcinogenic effects on animal or humans and induce various cancers. Polycyclic aromatic hydrocarbons are a consequence of environmental pollutants, imperfect burning or pyrolysis of organic substances during industrial processing. Additionally, foods can be contaminated during their processing and preparation through different heat treatments. This review highlights the formation, occurrence and health impacts of PAHs in milk and milk products, and analytical technique used for their determination in dairy products.