Bioactive peptides derived from milk proteins and their health beneficial potentials: an update

It has been well recognized that dietary proteins provide a rich source of biologically active peptides. Today, milk proteins are considered the most important source of bioactive peptides and an increasing number of bioactive peptides have been identified in milk protein hydrolysates and fermented dairy products. Bioactive peptides derived from milk proteins offer a promising approach for the promotion of health by means of a tailored diet and provide interesting opportunities to the dairy industry for expansion of its field of operation. The potential health benefits of milk protein-derived peptides have been a subject of growing commercial interest in the context of health-promoting functional foods. Hence, these peptides are being incorporated in the form of ingredients in functional and novel foods, dietary supplements and even pharmaceuticals with the purpose of delivering specific health benefits.     

Major advances in concentrated and dry milk products, cheese, and milk fat-based spreads

Advances in dairy foods and dairy foods processing since 1981 have influenced consumers and processors of dairy products. Consumer benefits include dairy products with enhanced nutrition and product functionality for specific applications. Processors convert raw milk to finished product with improved efficiencies and have developed processing technologies to improve traditional products and to introduce new products for expanding the dairy foods market. Membrane processing evolved from a laboratory technique to a major industrial process for milk and whey processing. Ultra-filtration and reverse osmosis have been used extensively in fractionation of milk and whey components. Advances in cheese manufacturing methods have included mechanization of the making process. Membrane processing has allowed uniform composition of the cheese milk and starter cultures have become more predictable. Cheese vats have become larger and enclosed as well as computer controlled. Researchers have learned to control many of the functional properties of cheese by understanding the role of fat and calcium distribution, as bound or unbound, in the cheese matrix. Processed cheese (cheese, foods, spreads, and products) maintain their importance in the industry as many product types can be produced to meet market needs and provide stable products for an extended shelf life. Cheese delivers concentrated nutrients of milk and bio-active peptides to consumers. The technologies for the production of concentrated and dried milk and whey products have not changed greatly in the last 25 yr. The size and efficiencies of the equipment have increased. Use of reverse osmosis in place of vacuum condensing has been proposed. Modifying the fatty acid composition of milkfat to alter the nutritional and functional properties of dairy spread has been a focus of research in the last 2 decades. Conjugated linoleic acid, which can be increased in milkfat by alteration of the cow's diet, has been reported to have anticancer, anti-atherogenic, antidiabetic, and antiobesity effects for human health. Separating milk fat into fractions has been accomplished to provide specific fractions to improve butter spreadability, modulate chocolate meltability, and provide texture for low-fat cheeses.     

Invited review: bovine studies on optimal lengths of dry periods

Milk production per cow has increased as a result of progressive changes in the genetics and management of the dairy animal population. A management constant during many decades of progress has been the widely adopted dry period length of 51 to 60 d. The scientific basis for that industry standard was examined to assess its validity as the appropriate standard for the modern dairy industry. If subsequent milk yields can be sustained fully after dry periods that are shorter than the current standard, then considerable milk is being forfeited by retaining longer dry periods. Conversely, failure to allow any dry period will result in a significant decrease in subsequent milk synthesis and secretion. Most studies to determine the minimum length of dry period required have involved retrospective analyses of observational data. Only five experiments have been reported in which dairy cows were assigned, at random, to planned 30- and 60-d dry periods. Estimates of the change in subsequent milk production when days dry were decreased from 50 to 57 d to 30 to 34 d ranged from a 10% decrease to a 1% increase. However, lower yields after shorter dry periods may be partially offset by greater milk yields in the previous lactation if such cows are milked 3 to 4 wk longer. Environmental factors that influence milk production as well as the biological processes that occur within the mammary gland during the nonlactating period must be considered when dry period lengths are compared. Importantly, additional animal trials that specifically assign cows randomly to the dry period lengths to be evaluated are needed to determine optimal dry period lengths for modern dairy cows in differing management scenarios.     

Current Immunoassay Methods for the Rapid Detection of Aflatoxin in Milk and Dairy Products

The presence of mycotoxins in foodstuff causes serious health problems to consumers and economically affects the food industry. Among the mycotoxins, aflatoxins are very toxic and highly carcinogenic contaminants which affect the safety of many foods, and therefore endanger human health. Aflatoxin M₁ (AFM₁) found in milk results from the biotransformation of aflatoxin B₁. Many efforts have been made to control the source of AFM₁ from farmers to dairy product companies. However, AFM₁ escapes ordinary methods of food treatment such as cooking, sterilization, and freezing, hence it appears in milk and dairy products. The presence of high levels of AFM₁ constitutes an alarming threat as milk and dairy products contain essential nutrients for human health, especially for infants and children. For this reason, there is a pressing need for developing a fast and reliable screening method for detecting trace aflatoxins in food. Several analytical methods based on high‐performance liquid chromatography (HPLC) and mass spectroscopy have been used for aflatoxin detection; however, they are expensive, time‐consuming, and require many skills. Recently, immunoassay methods, including enzyme‐linked immunosorbent assay (ELISA), immunosensors, and lateral flow immunoassay (LFIA), have been preferred for food analysis because of their improved qualities such as high sensitivity, simplicity, and capability of onsite monitoring. This paper reviews the new developments and applications of immunoassays for the rapid detection of AFM₁ in milk.     

Aspects of milk-protein-stabilised emulsions

Milk proteins are widely used as ingredients in prepared foods, in which they perform a wide range of key functions, including emulsification, thickening, gelling and foaming. An important functionality of milk proteins in food colloids is their ability to facilitate the formation and stabilisation of oil droplets in emulsions. The ability of milk proteins to adsorb at the oil–water interface and to stabilise emulsions has been exploited by the food industry in the manufacture of nutritional products, specialised medical foods, dietary formulations, cream liqueurs and dairy desserts. This article provides an overview of the properties and functionalities of food emulsions formed with milk proteins, focusing on the structure and composition of adsorbed protein layers, competition between proteins and the physical and chemical stability of emulsion droplets. Of particular importance is the understanding of the behaviour of milk-protein-based emulsions under the conditions relevant to digestion in the human gastrointestinal tract. Recent relevant research in this area is reviewed and discussed.     

Invited review: Dairy intake and bone health: a viewpoint from the state of the art

The aim of this review was to focus on the complex relationships between milk and dairy products intake and bone health, with particular emphasis on osteoporosis. The literature was extensively examined to provide an objective overview of the most significant achievements on the subject. Osteoporosis can be defined as a disease characterized by low bone mass and microarchitectural deterioration of bone tissue, leading to enhanced bone fragility and a consequent increase in fracture risk. Although the major determinants of peak bone mass and strength are genetic, major factors during childhood and adolescence may affect the ability to achieve peak bone mass. These include nutrition, particularly calcium and protein intake, physical activity, endocrine status, as well as exposure to a wide variety of risk factors. The role of calcium intake in determining bone mineral mass is well recognized to be the most critical nutritional factor to achieve optimal peak bone mass. The greatest amount of dietary calcium is obtained from milk and dairy foods, which also provide the human diet with vitamin D (particularly for products fortified with vitamin D), potassium, and other macro- and micronutrients. Although studies supporting the beneficial effects of milk or calcium on bone health are predominant in the literature, perplexity or discordance on this subject was expressed by some authors. Discordant data, mainly on the risk of fractures, provided limited proof of the unfavorable effect of dairy intake. More often, discordant works indicate no effect of dairy consumption on bone safety. Some considerations can be drawn from this viewpoint. Milk and dairy products are an optimal source of calcium as well as of other limiting nutrients (e.g., potassium and magnesium), with important effects on bone health. Bioactive components occurring in milk and dairy products may play an essential role on bone metabolism, as shown by in vivo and in vitro studies on colostrum acidic proteins and milk basic proteins. Calcium intake positively affects bone mass and is crucial in childhood and youth for correct bone development. In elderly people, calcium intake as well as vitamin D availability should be carefully checked. As a general conclusion, calcium is essential for bone health, although it will not prevent bone loss due to other factors; in this context, milk and dairy foods are bioavailable, relatively inexpensive sources of calcium for the human diet.     

Investigation of the Putative Associations Between Dairy Consumption and Incidence of Type 1 and Type 2 Diabetes

A growing body of evidence suggests a possible relationship between the consumption of dairy products and the incidence of diabetes. A positive correlation between the early introduction of dairy in infancy and the incidence of type 1 diabetes (T1D) in genetically predisposed infants has been suggested by studies on rodents and humans. However, the lines of evidence supporting this association, including epidemiological studies and the observation of antibodies to bovine serum albumin, β-casein and bovine insulin in the serum of patients with T1D, are not without controversy. On the other hand, an inverse relationship between the consumption of dairy foods and the development of metabolic syndrome and/or type 2 diabetes (T2D) has been implied by epidemiological studies. Several dairy components, especially milk proteins, are believed to play a role in the beneficial effect of dairy consumption on glucose regulation by modulation of incretin hormones. Other dietary factors have also been associated with the incidence of T1D and T2D, indicating that dairy foods might be only one among many dietary agents possibly implicated in the development of diabetes. The present paper critically reviews the evidence and plausible mechanisms for the putative associations between dairy food consumption and incidence of T1D and T2D.     

Peptides from milk proteins and their properties

This review has attempted to study the literature pertaining to peptides derived from milk proteins. Hydrolysis of milk proteins to generate peptides has been practiced for a long time and it was recognized early on in this process that the taste of hydrolyzates might hinder use of these products in food formulations. Modification of protein is necessary to form a more acceptable or utilizable product, to form a product that is less susceptible to deteriorative reactions and to form a product that is of higher nutritionall quality. Modifications may be achieved by a number of chemical and enzymatic means. This review has considered only enzymatic modification of dairy proteins. Modified proteins contain peptides and some of these peptides have been purified and their functionalities have been compared with unmodified proteins. This paper has examined the literature pertaining to improvement in functionality of enzyme-modified proteins. Improvements in solubility, emulsification, foaming and gelation were examined. There is limited information available on the sequence of the peptides necessary to improve the functional characteristics of proteins. Knowing the sequences of desirable functional peptides can lead to genetic alteration of proteins to improve functionality. Addition of synthetic peptides to intact proteins may be another way in which the functionality of proteins can be augmented. Some of the peptides in milk proteins are capable of affecting biological functions of an organism. These effects can be antimicrobial and probiotic, i.e., prevent the growth and proliferation of undesirable and pathogenic organisms, or they may promote the growth of desirable bacteria in the digestive tract of humans and animals. Peptides derived from milk protein have been shown to exert digestive and metabolic effects as well. They may also influence the immune system. These biological effects may play an important role in the development of medical foods that treat or mitigate the effects of diseases. Proteins are allergens and therefore it is possible that products derived from modification of proteins may also be allergens. The known literature about the allergenicity of peptides derived from milk proteins has been examined in this article. Last, but not the least, the taste attributes of peptides is also considered. Bitterness of hydrolyzates is a common occurrence and the origins of these bitter peptides and possible ways of mitigating this sensory defect has been discussed. Many of the peptides that enhance functionality and exert biological activity are likely to be bitter. Therefore, the bitter taste of hydrolysis products has to be dealt with in boosting the functional or nutraceutical aspects of foods containing these peptides. Analytical techniques for sequencing peptides have become more accessible and purification of peptides is commercially feasible. Computer based modeling techniques have aided the prediction of structures in these peptides. These advances, coupled with the advances in biotechnology, promise to revolutionize the future of nutraceutical and functional foods.