Carotenoids and retinoids in human nutrition.

Since the discovery of vitamin A as a fat-soluble growth factor in the early part of the century, research into carotenoids and retinoids has attracted the attention of many scientists. These two groups of compounds are still being actively studied all over the world since many gaps in knowledge exist and new frontiers are being pursued. Recent developments in studies into the possible roles of carotenoids and retinoids beyond their classical functions in vision have created a great deal of excitement in the biomedical community. This review covers a wide range of topics pertaining to these two closely related compounds. Particular emphasis is given to the functions of these compounds and their roles in human nutrition. Various aspects of vitamin A deficiency and studies on carotenoids and retinoids in cancer development and prevention are reviewed in some detail.     

Technical note: Measurement of total estrone content in foods. Application to dairy products

Estrone is a powerful growth-inducing hormone that is present in milk, mainly in the form of fatty acid esters, at concentrations that promote growth in experimental animals. We present here a method useful for the measurement of this natural hormone in foods and applied it to several common dairy products. Samples were frozen, finely powdered, and lyophilized then extracted with trichloromethane/methanol; the dry extract was saponified with potassium hydroxide. The free estrone evolved was extracted with ethyl acetate and was used for the estimation of total estrone content through radioimmunoassay. Application of the method to dairy products showed high relative levels of total estrone (essentially acyl-estrone) in milk, in the range of 1 microM, which were halved in skimmed milk. Free estrone levels were much lower, in the nanomolar range. A large proportion of estrone esters was present in all other dairy products, fairly correlated with their fat content. The amount of estrone carried by milk is well within the range, where its intake may exert a physiological response in the sucklings for which it is provided. These growth-inducing and energy expenditure-lowering effects may affect humans ingesting significant amounts of dairy products.     

Microstructure of dairy foods. 2. Milk products based on fat

Cold-stage scanning electron microscopy and transmission electron microscopy of replicas of freeze-fractured samples have been suggested as the electron microscopic techniques best suited to study the microstructure of milk products based on fat. New developments in other techniques such as fixation of fat with imidazole-buffered osmium tetroxide and embedding in a resin also have been mentioned. Microstructure of various forms of cream, ice cream, cream cheese, cream cheese spread, and butter, established by the techniques mentioned, has been reviewed with respect to the specific properties of each of the fat-based milk products.     

Probiotic bacteria: selective enumeration and survival in dairy foods

A number of health benefits have been claimed for probiotic bacteria such as Lactobacillus acidophilus, Bifidobacterium spp., and Lactobacillus casei. Because of the potential health benefits, these organisms are increasingly incorporated into dairy foods. However, studies have shown low viability of probiotics in market preparations. In order to assess viability of probiotic bacteria, it is important to have a working method for selective enumeration of these probiotic bacteria. Viability of probiotic bacteria is important in order to provide health benefits. Viability of probiotic bacteria can be improved by appropriate selection of acid and bile resistant strains, use of oxygen impermeable containers, two-step fermentation, micro-encapsulation, stress adaptation, incorporation of micronutrients such as peptides and amino acids and by sonication of yogurt bacteria. This review will cover selective enumeration and survival of probiotic bacteria in dairy foods.     

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.     

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。     

Milk intolerance and microbe-containing dairy foods

The relationship between primary lactase deficiency, the amount of lactose in the diet, and symptoms of intolerance continues to be debated. Primary adult lactase deficiency is common with a worldwide occurrence of near 70%. Lactase-deficient individuals malabsorb lactose but may or may not show intolerance symptoms. The development of symptoms appears to depend on the dose of lactose ingested, whether it is accompanied by a meal or other food, rate of gastric emptying, and small intestine transit time. Lactose loads of 15 g or greater produce symptoms in the majority of lactase-deficient persons. However, when lactose loads of up to 12 g are fed, symptoms can be minimal or absent. Tolerance to yogurt, acidophilus milk, and other microbe-containing dairy foods has been suggested and is thought to be due to either a low lactose content or in vivo autodigestion by microbial beta-galactosidase. Up to 20 g of lactose in yogurt is tolerated well by lactase-deficient persons. Associated with the consumption of yogurt is a three- to fourfold reduction in lactose malabsorption as compared with similar lactose consumption in milk. Improved lactose digestion appears due to autodigestion by microbial beta-galactosidase. This enzyme may be released from yogurt culture by gastric or bile acid digestion. Feeding yogurt that was pasteurized following fermentation, with only trace amounts of microbial beta-galactosidase activity, results in a threefold increase in lactose malabsorption as compared with feeding yogurt with a viable culture. However, pasteurized yogurt also is tolerated well by lactase-deficient persons, suggesting that tolerance of up to 20 g of lactose in yogurt may be independent of lactose malabsorption. The enhanced lactose absorption and tolerance observed with yogurt feeding are not apparent when unfermented acidophilus milk or cultured milk are fed.     

Packaging system and probiotic dairy foods

The consumption of foods containing probiotic cultures has greatly increased over the past years as a result of their benefits to human health. Along with other factors, the choice of the packaging material plays an important role in maintaining viable counts of these microorganisms at sufficiently high levels to assure their therapeutic activity throughout shelf-life. The aim of this article is to provide an overview of the main issues related to the importance of the packaging system and/or materials on the stability of probiotic dairy foods.     

Invited review: Sensory analysis of dairy foods

Sensory quality is the ultimate measure of product quality and success. Sensory analysis comprises a variety of powerful and sensitive tools to measure human responses to foods and other products. Selection of the appropriate test, test conditions, and data analysis result in reproducible, powerful, and relevant results. Appropriate application of these tests enables specific product and consumer insights and interpretation of volatile compound analyses to flavor perception. Trained-panel results differ from dairy judging and grading and one objective of this review is to clearly address and demonstrate the differences. Information on available sensory tests, when and how to use them, and the powerful results that can be obtained is presented.     

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: A review

Milk and dairy products continue to raise concerns with regard to contamination with mycotoxins, most of which have a likely or confirmed carcinogenic status. Such concerns are more serious for certain cheeses due to their frequent contamination with high concentrations of mycotoxins from various sources, including the milk used as a raw material and moulds found as contaminants or purposely added for ripening. Different control measures have been suggested to prevent the formation or to remove mycotoxins in dairy products once formed therein. However, these methods either provide an insufficient degree of protection or are onerous to implement. This review surveys the main mycotoxins associated with dairy products and discusses their health significance. Attention is drawn to the lack of knowledge on the emerging and masked mycotoxins with relevance to dairy products. Known control measures are discussed from the perspective of their application while presenting their strengths and weaknesses.     

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.     

The shelf-life of dairy products: 3. Factors influencing intermediate and long life dairy products

In this, the third part of a series of four reviews, the factors -which control the shelf-life of long and intermediate life dairy products are discussed. Two distinct types of product degradation are addressed. Firstly, the degradative potential of heat-resistant lipase, protease and phospholipase, derived from psychrotrophic bacteria commonly found in refrigerated milk, is examined. Secondly, the chemical composition of milk is reviewed and lipid oxidation, calcium induced aggregation of milk protein and Maillard reaction are identified as likely routes to product spoilage. The relative importance of these reactions to specific products will be discussed in the final part of this series of articles.     

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.     

Fermented dairy products: knowledge and consumption.

PURPOSE: Much has been published on the nutritional and health benefits of fermented dairy products, especially those containing probiotic microorganisms. However, consumers may not be familiar with the term "fermented dairy products," and therefore may not take full advantage of them. University students' knowledge and consumption patterns of fermented dairy products were assessed. METHODS: University students (n=223) completed a survey consisting of a section on demographics and another on knowledge and consumption patterns. RESULTS: The majority of respondents (62%) were not familiar with the term "fermented dairy products." Most respondents consumed yogourt a few times a week (40%) or a few times a month (30%). Almost all respondents (92%) were unable to identify the difference between regular and probiotic yogourt. Most respondents (93%) had not heard of acidophilus milk, but the majority (65%) would be willing to try it. Most respondents were unsure whether sour cream (65%), yogourt beverages (74%), and cheddar cheese (61%) were fermented dairy products. Sixty percent of respondents never consumed yogourt drinks. CONCLUSIONS: Education is needed about fermented dairy products, especially probiotics, and their nutritional and health benefits. Such education may increase their acceptability and consumption.     

Invited review: Sugar reduction in dairy products

Sugar overconsumption continues to increase worldwide and contributes to multiple health-related issues. Dairy foods represent a large market, grossing more than $125 billion per year worldwide. Consumer demands for healthier products are leading to a large push for sugar reduction in dairy foods. Sugar plays an important role in dairy foods, not only in flavor but also in texture, color, and viscosity. Replacing sugar can have negative effects, making substitution inherently difficult. Natural and artificial nonnutritive sweeteners exist for sugar reduction. Natural nonnutritive sweeteners are popular, particularly for label appeal, but many consumers still prefer the taste of artificial nonnutritive sweeteners. Sweet taste perception can also be affected by texture of the food matrix and the presence of fat. Other sugar reduction techniques include hydrolysis of lactose, ultrafiltration, and direct reduction. This review will address the role of sugar, alternative sweeteners, and sugar reduction in ice cream, yogurt, and flavored milk.