Milk Proteins: From Expression to Food

By Harjinder Singh

Milk Proteins: From Expression to Food, Third Edition contains contributions from internationally recognized authors from academia and industry. Professionals, academics and graduate students working in any of the dairy-related industries or disciplines will continue to find this updated information valuable to their work. Using a unique "field-to-table" approach, this third edition provides comprehensive coverage of new developments and insights into the entire dairy food chain – from the source, to the nutritional aspects affecting the customer.

Containing three new chapters, this new edition continues to present a comprehensive overview of the biology, processing, chemistry, and nutrition of milk proteins and features the latest science and developments. Valuable application-based information is made available through the exploration of the use of milk proteins from industry viewpoints.

• Presents a comprehensive overview of the biology, processing, chemistry and nutrition of milk proteins
• Features the latest science and developments
• Explores the use of milk proteins from industry viewpoints
• Features internationally recognized editors and authors who bring academic and industrial insights to this important topic

• Language: English
• Publisher: Academic Press
• Release date: Nov 20, 2019
• ISBN: 9780128152522

Book preview

reality.

Chapter 1

World supply of food and the role of dairy protein

Mike Bolanda; Jeremy Hilla,b    a The Riddet Institute, Massey University, Palmerston North, New Zealand

b Fonterra Co-operative Group, Palmerston North, New Zealand

Abstract

World hunger continues to be a major problem. The main focus is on the availability of adequate calories for all, but this overshadows another problem: the availability of enough protein and enough of the dietary essential amino acids. We estimate that about a quarter of the world's population is getting barely enough protein and that there is a particular issue with the essential amino acid lysine, which is deficient in cereal proteins, the biggest source of protein nutrition. Milk protein is an important source of dietary protein and is particularly rich in lysine and branched-chain amino acids. It accounts for 10% of all the global protein supply, the third highest supply after cereals and meat; however, it is more important than the amounts would suggest because of its rich supply of essential amino acids and high digestibility (in contrast to cereal protein) and because of its acceptability to vegetarians. Global trade in dairy is still small (about 11% of dairy production is traded) but growing. Supplementation of cereal protein with milk protein has a potentially important role to play in balancing world protein nutrition.

Keywords

Protein nutrition; Milk protein; Dairy trade; Dairy production

Introduction and outline of chapter

As one of the basic necessities of life, the availability, quality, and affordability of food are of concern to individuals and nations alike. The Green Revolution started in the late 1960s and involved the introduction of high-yielding new seed varieties and better use of irrigation and fertilizers. Following this, the world enjoyed several decades of relative stability in the price of basic items of food, including food grains. The period from the early 1970s to 1990 saw the world output of food grains, and oilseeds rise steadily by an average of 2.2% a year, with periodic fluctuations. With the exception of parts of the African continent, the rate of growth of food crops exceeded that of the world population, leading to an increase in their per capita availability, and to relatively stable prices. Indeed, world food prices in real terms were at their lowest in 100 years in 2000 (Trostle, 2008). However, from the early 1990s, the global rate of the growth of grain and oilseed production declined, reaching a net 0% for the decade to 2016. Over the same decade, milk production grew by, on average, 2%.

The inflation-adjusted Food and Agriculture Organization (FAO) of the United Nations Food Price Index stood at 141.1 points in October 2018, having risen from its 2002 to 2004 base of 100.0 points (FAO, 2018) and reached a high of 229.9 points in 2011. The October 2018 decline in the Food Price Index was the result of falling dairy, meat, and oil prices, which more than offset a surge in sugar prices and a more moderate increase in the prices of cereals. The FAO Dairy Price Index averaged 181.8 points in October 2018, continuing a downward trend for a fifth consecutive month. The price decrease reflects the growing evidence of increased export supplies across all major dairy products. In contrast, the FAO Cereal Price Index averaged 166.3 points in October 2018, representing a 13.6 point (8.9%) year-on-year increase. Among the major cereals, maize quotations from the United States firmed the most, supported by strong export sales, and wheat prices also averaged higher, driven by a tighter supply outlook, especially in view of deteriorating crop prospects in Australia.

Side by side with this worsening situation with respect to the availabilities and prices of the major cereals, there has been another recent development involving food consumption patterns in a number of countries. With growing affluence, tastes change, and consumers shift to more varied diets, which usually include larger proportions of noncereal items. Over the last few decades, several poorer countries, among them, the two most populous, namely, China and India, have experienced rapid growth and transformation in their economies. This has helped to lift several million people out of extreme poverty and to make many others more affluent, bringing in its trail significant changes in food consumption. One of the more noticeable changes has been an increase in the consumption of animal protein. These developments have important policy implications for the global food economy. At the same time, hunger still afflicts a large number of people globally and is in need of policies to resolve or mitigate it.

This chapter examines several interrelated issues relating to the evolving world food situation. In particular, it investigates the issue of nutrition and the role of proteins and their constituent amino acids. It starts by looking at the issue of hunger, its measurement, its global incidence, and mitigation targets. It then addresses the issue of nutrition, its global and regional perspectives, and the role of animal and vegetable proteins. The evolving global demographic trends, with a rapidly increasing elderly population that has special nutritional needs, call for policies to deal with the issue of nutrition for the aged, and the role of proteins in it. As the production and the consumption of protein foods in different countries do not always match, significant international trade in protein products exists. This is briefly discussed to identify the major players in the global protein markets. The chapter concludes with some observations on the policy implications deriving from its discussions. In the examination of proteins in their various dimensions, the particular focus of this chapter is the evolving role of dairy proteins and its implications for future policy.

Hunger and need for food

Every day, millions of people around the globe do not get enough food to eat and remain hungry. Hunger has been referred to as the uneasy or painful sensation caused by a lack of food and the recurrent and involuntary lack of access to food (Anderson, 1990). There is no assurance that these hungry people will get the minimum required quantity of food on a daily basis. This unpredictability about where the next meal will come from is called food insecurity. The FAO (2000) defines food insecurity as: "A situation that exists when people lack secure access to sufficient amounts of safe and nutritious food for normal growth and development and an active and healthy life."

Following this definition, people are hungry if they do not get enough energy supply from food (fewer than about 1800 kilocalories a day), or if the food they consume is not of sufficiently high quality (containing essential nutrients). Hunger is usually understood to refer to the discomfort associated with a lack of food (von Grebmer et al., 2012).

Hunger-reduction targets

The United Nations 2030 Agenda for Sustainable Development (United Nations, 2015a) is a framework for advancing the well-being of humankind. It aims to ensure peace and prosperity for all on a healthy planet. The 17 sustainable development goals address global challenges related to poverty, inequality, climate, environmental degradation, prosperity, and peace and justice and are targeted to be reached by 2030. Goal 2 specifically addresses hunger and is simply stated as: Goal 2: Zero Hunger. The goal has five subgoals.

2.1 By 2030, end hunger and ensure access by all people, in particular the poor and people in vulnerable situations, including infants, to safe, nutritious, and sufficient food all year round.

2.2 By 2030, end all forms of malnutrition, including achieving, by 2025, the internationally agreed targets on stunting and wasting in children under 5 years of age, and address the nutritional needs of adolescent girls, pregnant and lactating women, and older persons.

2.3 By 2030, double the agricultural productivity and incomes of small-scale food producers, in particular women, indigenous peoples, family farmers, pastoralists, and fishers, including through secure and equal access to land, other productive resources and inputs, knowledge, financial services, markets and opportunities for value addition, and nonfarm employment.

2.4 By 2030, ensure sustainable food production systems and implement resilient agricultural practices that increase productivity and production; that help to maintain ecosystems; that strengthen capacity for adaptation to climate change, extreme weather, drought, flooding, and other disasters; and that progressively improve land and soil quality.

2.5 By 2020, maintain the genetic diversity of seeds, cultivated plants, and farmed and domesticated animals and their related wild species, including through soundly managed and diversified seed and plant banks at the national, regional, and international levels, and promote access to and fair and equitable sharing of benefits arising from the utilization of genetic resources and associated traditional knowledge, as internationally agreed.

Goal 2.2 is particularly important with respect to protein supply, as insufficient protein is one of the major contributors to childhood stunting. According to the United Nations, childhood stunting is one of the most significant impediments to human development, globally affecting approximately 162 million children under the age of 5 years. Stunting, or being too short for one's age, is defined as a height that is more than two standard deviations below the World Health Organization (WHO) Child Growth Standards median. It is a largely irreversible outcome of inadequate nutrition and repeated bouts of infection during the first 1000 days of a child's life (WHO, 2014).

In 2012, the World Health Assembly Resolution 65.6 endorsed a comprehensive implementation plan on maternal, infant, and young child nutrition. It specified six global nutrition targets for 2025, with the first target being a 40% reduction in the number of children under 5 years who are stunted (WHO, 2014).

World hunger and undernutrition status

According to the most recent FAO report, the total number of undernourished people in the world was estimated to be 815 million in 2016, up from 777 million in 2015 although still down from about 900 million in 2000 (FAO et al., 2017). The largest numbers of undernourished people live in the developing countries. More than half live in just seven countries (Bangladesh, China, the Democratic Republic of the Congo, Ethiopia, India, Indonesia, and Pakistan) and over 40% live in China and India alone (data from FAO et al., 2017). The territory with the highest number of undernourished people is sub-Saharan Africa, with an estimated 307 million (Fig. 1.1). The food security situation has worsened in recent times, in particular in parts of sub-Saharan Africa, South-Eastern Asia, and Western Asia. Deteriorations have been observed most notably in situations of conflict and conflict combined with droughts or floods (FAO et al., 2017).

Fig. 1.1 Undernourishment (severe food insecurity) in 2016, by region (millions). Data from FAO, IFAD, UNICEF, WFP, WHO, 2017. The State of Food Security and Nutrition in the World 2017. Building Resilience for Peace and Food Security. Food and Agriculture Organization of the United Nations, Rome, Italy.

Global hunger index

The International Food Policy Research Institute has introduced the Global Hunger Index (GHI) tool to measure and track global hunger. The index combines three hunger indicators as follows: (1) the number of the undernourished as a proportion of the total population, (2) the proportion of underweight children under the age of 5 years, and (3) the mortality rate of children under the age of 5 years. The three indicators are assigned equal weights. On a 100-point scale, the higher is the value of the index, the worse is the incidence of hunger, implying that a score of 0 indicates no hunger and a score of 100 indicates the worst possible hunger—both of these extremes are, obviously, just notional and not observed in practice. Different hunger scenarios are defined with the help of the GHI. An index value of less than 4.9 indicates low hunger; values between 5 and 9.9 indicate moderate hunger; values between 10 and 19.9 indicate serious hunger; values between 20 and 29.9 indicate alarming hunger; values in excess of 30 indicate extremely alarming hunger.

The 2017 world GHI showed improvement over the 2000 value, decreasing by 27%. The countries of greatest concern (rated alarming or extremely alarming) are mostly in sub-Saharan Africa. At the regional level, South Asia and Africa south of the Sahara have the highest 2017 GHI scores, indicating serious levels of hunger. Fig. 1.2 graphs these values for the different regions.

Fig. 1.2 Global and regional trends of the Global Hunger Index: contribution of components in 1992, 2000, 2008, and 2017. From von Grebmer K., Bernstein J., Hossain N., Brown T., Prasai N., Yohannes Y., Patterson F., Sonntag A., Zimmermann S.-M., Towey O., Foley C., 2017. 2017 Global Hunger Index: The Inequalities of Hunger. International Food Policy Research Institute, Washington, DC. Reproduced with permission from the International Food Policy Research Institute, www.ifpri.org. The publication from which this figure originates can be found online at https://doi.org/10.2499/9780896292710.

The importance of protein in world nutrition

Most reports on hunger and undernutrition are primarily focused on calories and rightly so. If a person does not get enough calories, their well-being will be compromised. However, calories are a necessary, but not sufficient, condition for good nutrition. Many nutrients and micronutrients, such as essential fatty acids, omega-3 lipids, and complex lipids, as well as vitamins and minerals, are also an important part of the diet, but are not the focus of this discussion.

A further aspect of undernutrition occurs when people are not getting enough protein and particularly not enough of the dietary essential amino acids. This aspect of undernutrition and the role of dairy protein in meeting these needs are the focus of the rest of this chapter. Table 1.1 lists the recommended daily intake of protein and of the dietary essential amino acids. It is necessary to have an adequate intake of total protein and of all the essential amino acids to maintain health.

Table 1.1

Data from WHO, 2007. Protein and Amino Acid Requirements in Human Nutrition: Report of a Joint FAO/WHO/UNU Expert Consultation. World Health Organization, Geneva, Switzerland.

Protein and its composition and bioavailability

The assessment of protein nutrition is more complex than that for calories, because proteins vary widely in terms of their composition and bioavailability.

Protein composition

All proteins are composed of linear chains of amino acids, and each species of protein has its own defined amino acid sequence, which is determined by the genetics of the producing organism. Thus, the amino acid composition and, by implication, the amount of each essential amino acid in a given protein are defined. In practice, most food protein sources contain a complex mixture of proteins; nevertheless, the overall composition can be determined empirically and is generally quite constant over time and geographic origin. This has enabled the compositions of almost all the major food protein sources in terms of essential amino acids to be determined, and thus, intakes of dietary essential amino acids can be estimated from the knowledge of the types and amounts of food protein in a diet. In practice, it turns out that the intake of most essential amino acids in most diets is adequate, provided the total protein intake is adequate (although the timing of intake is also important—see later in this chapter). The exception to this is the dietary essential amino acid lysine. This is discussed in detail later in this chapter.

Bioavailability

Adequate protein supply is one aspect of protein nutrition. A further important aspect is bioavailability: getting the amino acids from the food structures in the gastrointestinal tract to the cells that need them throughout the body. In the adult gastrointestinal tract, proteins must be broken down to very small oligopeptides (at most di- or tripeptides) to be taken up and to single amino acids to enter most metabolic pathways. Thus, it is necessary for the protein in foods to be both accessible to digestive enzymes and broken down by the digestive enzymes in the stomach and small intestine in particular. Furthermore, it is necessary that the broken-down protein is able to be taken up into the bloodstream, where it can be redistributed to the tissues that need it. The efficiency of the digestion of most of the common food protein sources has been determined, using a range of different methods. Past methodology has largely been based on so-called fecal digestibility. This method is now known to be flawed, particularly with respect to foods with poor digestibility; however, it has been widely used and is the only method for which literature values for most common foods are available. For a full discussion on protein quality and nutritional requirements, the reader is referred to an FAO report on Protein quality evaluation in human nutrition (FAO, 2013).

Using digestibility values, dietary intakes can be converted to an estimated uptake into the body for these proteins, noting that, as these values are derived from a flawed methodology, particularly in the case of plant-derived proteins, they represent an upper limit of their true bioavailability. The digestibilities of a range of dietary proteins are given in Fig. 1.3.

Fig. 1.3 True protein digestibility of common food proteins. Data from FAO, 1970. Amino-Acid Content of Foods and Biological Data on Proteins. Food and Agriculture Organization of the United Nations, Rome, Italy, http://www.fao.org/docrep/005/ac854t/ac854t00.htm (Accessed 10 February 2011).; WHO/FAO, 1991. Protein Quality Evaluation. Report of Joint FAO/WHO Expert Consultation. Food and Agriculture Organization, Rome, Italy.

Animal-derived proteins generally have good bioavailability and content of dietary essential amino acids, but many plant proteins are deficient in one or more dietary essential amino acids, and many are not efficiently digested, and therefore, the constituent amino acids are not highly bioavailable. As most western countries are characterized by a high-protein diet with a strong emphasis on animal-derived protein, protein nutrition is not generally a problem (although there may be some issues with the protein nutrition of the elderly, as discussed later in this chapter). Most developing countries are very dependent on plant protein as the main dietary source; that protein may be inadequate, because of poor digestibility and poor amino acid balance, particularly in the case of lysine.

World protein supply and its regional distribution

Information on the amount of protein available per capita and by protein source in each country is available from the FAOSTAT database (http://faostat.fao.org/). In Fig. 1.4, we present the average protein availability for individual countries, along with their total populations. This is presented as the total number of people who reside in countries with corresponding average protein availability for each incremental 5-g band.

Fig. 1.4 Protein availability by population on a country average basis. Each bar represents the total population of countries with average per capita daily protein availability in bands of 5 g per capita per day. Protein figures for 2013 from FAOSTAT September 2018; 2013 population data from United Nations, 2018. World Population Prospects 2017. Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat, New York, NY.

The figure is striking in having two clear peaks, one in the range 60–65 g of protein per capita per day and another in the range 95–100 g of protein per capita per day, with a considerable tail to the right.

The first of these peaks represents nearly a third of the world's population, including the populations of India and Indonesia. It is simple to calculate that, with a standard body weight of 70 kg and based on the dietary recommendations for protein requirements, a person will need 56-g protein/day to stay healthy. This band is 5–10 g of protein per capita per day more than that but will include a significant proportion of the population below this average. The band at 55–60 g of protein per capita per day is of greater concern as it is on the margin. It notably includes the countries of Bangladesh and the Philippines and a range of sub-Saharan African countries. This band is of great concern because, although the average availability figure is just above the minimum requirement, disparities of income and situation in these countries will mean that a large proportion of these people are not getting enough protein. Furthermore, these figures are for total protein supply only, with no correction for bioavailability. When the dietary pattern is corrected for the digestibility of the main protein components of the diet (from FAOSTAT), the situation is more serious, with more than 150 million people getting, on average, less than 55-g protein/day based on FAOSTAT figures for 2013. Although this is an improvement on the situation previously, there is still a large requirement to be met.

Plant and animal protein sources with a focus on dairy foods

In the consideration of global sustainability, there is considerable debate over the merits of vegetarianism and eating only vegetable-origin foods. It is often estimated that the production of 1 kg of animal-origin food requires 10 kg of plant-origin food, leading on to the simplistic assumption that 10 times as many people could be fed from the same resources if everyone was vegetarian. For a full discussion of the subject, the reader is referred to Fairlie (2010). In the case of dairy produce and eggs, the situation is somewhat better than it is for meat, because the animal can continue producing throughout its adult lifetime. This leads to conversion ratios of about 4:1. In fact, the argument is much more complex, partly because of the role of animals in subsistence agriculture, largely eating food waste or processing residue, or grazing and browsing plant species that are not suitable for human consumption and partly because of the niche many animals occupy in developed agricultural economies, either grazing pastures intensively or being farmed on country that is not suitable for arable cultivation (see, e.g., Elferink et al., 2008). In Livestock: On our plates or eating at our table? A new analysis of the feed/food debate by the FAO, it is estimated that, although livestock consume 6 billion tonnes of feed each year—including one-third of global cereal production—86% is composed of materials currently not eaten by humans (Mottet et al., 2017). In a recent analysis of the global food chain (Ritchie et al., 2018), it is estimated that 72 g of human-digestible protein per person per day is fed to livestock (all livestock, including monogastrics), but that meat and dairy (cows and buffaloes) on their own contribute more than half of this amount, that is, 37 g per person per day, to the human diet. In a simple analysis, we have calculated that, in the Canterbury Plains in New Zealand (the main wheat growing area), the yield per hectare per annum of protein from the wheat crop, processed to the form of white flour and its consequent baked products, is somewhat less that the yield of protein from milk that is produced over the same period in the same area. Thus, the efficiencies of production need to be considered in the context of what is the target of that production (there is no doubt that wheat produces the greater number of calories). Nevertheless, it must be recognized that the changing protein consumption patterns, involving more animal-based products, have significant implications for global land-use patterns, agriculture, agrifood industries, cereal prices, and the environment.

Growing global demand for animal proteins and implications

The demand for animal protein foods is expected to increase to about double the present consumption by 2050, driven off population growth and by emerging middle classes in developing countries (FAO, 2006). As people get more money, one of the first priorities is better food, and this usually means animal protein foods. This was first described by Bennett (1941), who related comparative studies of the consumption of staple foods, leading to what has come to be known as Bennett's law, the empirical generalization that there is an inverse relationship between the percentage of total calories derived from cereals and other staple foods and per capita income. This has since become generalized to mean a move away from carbohydrate-based foods to protein-based foods.

A simple extrapolation from past increases in animal production indicates that we should be able to meet this demand if past rates of increase can be sustained (Boland et al., 2013). However, past increases have been based on bringing in new land for farm production, increases in efficiency through breeding gains, better livestock management and nutrition, and other factors of the Green Revolution covered earlier. Most of these options are reaching their limits or entering a phase of diminishing returns in developed economies, but there is considerable scope for increased efficiencies of production in developing economies (Mottet et al., 2017). The carbon footprint of livestock production is a further constraint, although the good news is that, as animal production has intensified, the carbon footprint has massively decreased. For example, Capper et al. (2009) have calculated that the carbon footprint for milk in the United States in 2007 was just 37% of that for the same milk in 1944. Nonetheless, past increases will not continue, and infinitum and new ways of sustainably meeting the increasing demand are needed.

The dietary essential amino acids in proteins

Although there are nine dietary essential amino acids, it is rare for a diet with adequate overall protein intake to be deficient in any of them. The exception is lysine.

Lysine may be an issue for two reasons. The first is that many staple protein sources, particularly the cereals, are deficient in lysine. The second is that lysine is chemically unstable under heating and undergoes a range of reactions when food is heated. The most important of these is the Maillard reaction, in which the side chains of the lysine residues in the protein cross-react with sugar molecules to produce glycosyl lysine side chains that are indigestible and thus no longer bioavailable. This reaction can occur under mild heating conditions and, under more extreme conditions, is responsible for much of the browning of food that occurs on cooking. Another reaction of importance for dairy products is the reaction with phosphoserine, leading to the formation of lysinoalanine, which is not bioavailable. This problem is mostly restricted to casein-containing products (mainly milk powders and caseinate), because of their high phosphoserine content (see Chapter 11 for a detailed discussion of this reaction); however, it is seldom a nutritional problem because dairy proteins are rich in lysine.

Identifying the countries deficient in dietary essential amino acids

In an attempt to get an understanding of the dietary availability of the essential amino acids, countries with low intakes of protein were analyzed to determine the dietary essential amino acid content of the mix of protein sources for that country (from FAOSTAT), corrected for digestibility for each protein source. Because literature values were unavailable for some minor protein sources, a sensitivity test was performed, changing the digestibility figure from 1.0 to 0.8 for plant proteins and from 1.0 to 0.9 for animal proteins in these cases. As this change did not make a noticeable difference to the overall lysine bioavailability for the countries in question, the method was considered to be robust. The countries found to be lysine deficient are given in Table 1.2, together with information about the main dietary protein sources. It is noted that the number of countries and the degree of deficiency are considerably less than we have previously reported (Chatterjee et al., 2014).

Table 1.2

a RDI, recommended daily intake.

The countries that are lysine deficient show a clear pattern of low levels of consumption of animal protein and strong dependence on cereals for their protein.

Protein and dietary essential amino acid contents of food items

The amino acid composition and particularly the lysine content of proteins are of particular concern for countries that tend to be protein deficient. Thus, the maintenance of an adequate intake of lysine, particularly in populations with a high dependence on cereals, requires attention. Fig. 1.5 indicates the levels of bioavailable lysine in a range of common dietary protein sources. Meat is clearly the best source of lysine but may not be a suitable dietary component for many because of cost, of utility—as meat can be used in only a number of food applications and of cultural restrictions. Dairy protein is also an excellent source of lysine and can be used in a wide range of food applications. The inclusion of supplementary dairy protein in the diet may offer an effective solution that is acceptable to vegetarians, price notwithstanding.

Fig. 1.5 Bioavailable lysine content in a range of food proteins (in g/100 g protein, corrected for digestibility).

Demographic changes, aging populations, and the need for quality protein and dietary essential amino acids

Recent global demographic trends indicate a steady increase in the number of people aged 60 years and over. The projection is for this population to more than triple from 600 million in 2000 to over 2.1 billion in 2050 (United Nations, 2015b). As a consequence, in the more developed world, the fastest growing section of population is adults aged 80 years or over. This clearly presents unique challenges for healthcare, diets, and nutrition, as well as certain age-specific clinical conditions.

Both the number and the proportion of older persons are growing in virtually all countries, and these trends are likely to continue worldwide (United Nations, 2015b). In 2015, one in eight people worldwide was aged 60 years or over. By 2030, older persons are projected to account for one in six people globally. By the middle of the 21st century, one in every five people will be aged 60 years or over. Fig. 1.6 shows the predicted percentage of elderly population in 2050 in major continents. By 2050, it is projected that there will be more than 1.3 billion elderly people (> 60 years) in Asia alone.

Fig. 1.6 Percentage of elderly population in 2050 (numbers in millions). Data from United Nations, 2015b. World Population Ageing 2015 (ST/ESA/SER.A/390). Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat, New York, NY.

Aging is a continuous, ongoing, and progressive process of damage accumulation. It is associated with a reduction in muscle mass and function and reduced physical activity. The loss of muscle mass with aging is known as sarcopenia. With the aging of the population globally, the prevalence of sarcopenia is likely to increase. Sarcopenia is accelerated by inadequate diet, mainly because of a lack of quality protein in optimal quantity and a lack of essential amino acids. The issue of the nutritional needs of the growing aging population, in terms of the role of dietary protein and essential amino acids with particular reference to sarcopenia, is described in more detail in the following sections.

Overall, a strong case can be made that an aging population will require a substantially increased intake of protein, and of essential amino acids (particularly leucine), a demand that milk proteins are particularly well suited to meet.

Protein nutritional needs of the elderly

The aging process is characterized by changes in body composition, with a progressive loss of muscle and bone mass, strength, and metabolic function. The loss of muscle with aging is the result of a chronic imbalance between muscle protein synthesis and breakdown. There are many causes of sarcopenia, and an understanding of the complex mechanism is evolving. This degenerative loss of skeletal muscle occurs at a rate of 3%–8% per decade after the age of 30 years and accelerates with advancing age; chronic muscle loss is estimated to affect 30% of people older than 60 years and 50% of those older than 80 years (Katsanos et al., 2006; Paddon-Jones et al., 2008). With the aging of the population, the prevalence of sarcopenia and the resulting burden of disability are likely to increase. Strategies to prevent sarcopenia are, therefore, of considerable importance, and there is a need for public awareness, as simple health strategies can be effective.

Researchers have identified two measures that can play a role in the fight against sarcopenia: diet and exercise. However, in the case of many elderly individuals, the ability to perform exercise is compromised because of disease and disability. In this case, a daily high-quality protein intake can be helpful to slow or prevent muscle protein loss. Different protein sources have been found to stimulate muscle protein synthesis to varying degrees. The most important factor is the amount of essential amino acids in the protein, in particular, leucine. Differences in the digestibility and the bioavailability of certain protein-rich foods may also influence muscle protein synthesis (Paddon-Jones et al., 2008).

Currently, there is no agreement on whether dietary protein needs change with advancing age. For adults, the recommended dietary allowance (RDA) for protein is 0.8 g of protein per kilogram of body weight per day (WHO, 2007). It is recommended in the report of the FAO/WHO/UNU expert consultation, published in 2007, that the essential amino acid requirement for elderly people should be the same as that for adults, as the current acceptable methodologies are not apposite for making a separate set of essential amino acid values for elderly people (WHO, 2007). A more recent FAO-sponsored expert consultation has failed to resolve this. One group maintains that: The data based on the currently acceptable methodologies … are inadequate to make a separate recommendation for dietary IAA requirements in elderly people (Pillai and Kurpad, 2012); another group advises that: Dietary protein intake, and the resulting increased availability of plasma amino acids, stimulates muscle protein synthesis. If all other variables are controlled, increased muscle protein synthesis leads to improved muscle mass, strength and function over time. Increased muscle mass, strength and function are related to improved health outcomes in older individuals. Since adverse effects of reasonable increases in protein intake above the RDA of 0·8 g protein/kg/day have not been reported, it is reasonable to conclude that the optimal protein intake for an older individual is greater than the RDA (Wolfe, 2012).

It has been suggested in some studies that, instead of the RDA value, an intake of 1.0–1.5 g of protein per kilogram of body weight per day or about 15%–20% of the total caloric intake is essential to preserve a proper nitrogen balance in the healthy elderly (Morais et al., 2006; Wolfe et al., 2008). Many older people struggle to consume even the current recommended intake.

Role of essential amino acids in nutrition of the elderly

It is recognized that essential amino acids are mainly responsible for the stimulation of muscle protein anabolism in the aged (Volpi et al., 2003). It is considered that 15 g of essential amino acids taken as a bolus is required for maximum stimulation of muscle protein synthesis (Wolfe, 2002). This indicates that the quality of protein is very important in the diet of the elderly.

Preliminary data from a recent randomized controlled trial indicate that it is more important to ingest a sufficient amount (25–30 g) of high-quality protein with each meal rather than one large bolus, because more than 30 g in a single meal may not further stimulate muscle protein synthesis (Symons et al., 2009). It is also recognized in recent studies that the intake of whey protein brings beneficial effects to muscle protein anabolism in the elderly. Further, the ingestion of intact whey protein has been found to provide a greater anabolic benefit than the ingestion of the equivalent essential amino acids alone. Thus, whey protein may be more than just a simple source of essential amino acids with respect to providing a stimulus for enhancing muscle protein anabolism in the elderly (Katsanos et al., 2008). For a fuller discussion of the function of whey proteins and other milk proteins in human health, the reader is referred to Chapter 18 of this volume.

There is general agreement that the essential amino acid leucine increases protein anabolism and decreases protein breakdown (Paddon-Jones and Rasmussen, 2009). Leucine-rich food sources include legumes such as soybeans and cowpea and animal products such as beef, fish, and particularly dairy proteins (whey protein). It is reported that amino acid supplements without adequate leucine do not stimulate protein synthesis (Rieu et al., 2007; Hayes and Cribb, 2008). Leucine has recently been acknowledged to be especially important as a signaling molecule and a building block for muscle. Rat studies show that leucine can directly stimulate muscle protein synthesis through increasing mRNA translation (Anthony et al., 2000). Insulin and leucine are anabolic stimuli for muscle, and both share a common pathway of action via activation of a kinase known as mTOR. mTOR is the main regulator of cell growth and acts by phosphorylating target proteins involved in mRNA translation. Because insulin sensitivity decreases with age, one possible mechanism by which amino acids (mainly leucine) might improve muscle mass is by providing another anabolic stimulus to activate the mTOR-controlled pathway (Gaffney-Stomberg et al., 2009; Casperson et al., 2012).

No differences exist in the protein balance in the elderly relative to that in the young following the administration of either 30 g of beef protein or 15 g of essential amino acids as a bolus (Paddon-Jones et al., 2004). However, when 6.7 g of a mix of the dietary essential amino acids is given, the overall protein synthetic response is reduced in the elderly relative to the young (Katsanos et al., 2005). This anabolic resistance has been attributed to a decrease in leucine sensitivity and may be overcome by increasing the proportion of this amino acid in the diet. For example, when a 6.7-g bolus of dietary essential amino acids enriched with leucine (46% leucine compared with the 26% normally found in whey protein) was given to elderly individuals, protein synthesis was fully restored (Katsanos et al., 2006).

Global trade in proteins and the long term prospects, with a focus on dairy foods

Global food consumption patterns have been changing in recent decades in several significant ways. Among them is the noticeable and continuing shift in favor of proteins, especially animal proteins. The global consumption of protein is forecast to grow significantly by 2050, although the extent of this growth will depend upon various assumptions (Henchion et al., 2017). Henchion et al. (2017) determined that consumption would increase 32%–78% by 2050. The growth is largely due to the rising incomes in the developing world, more particularly in some of the more populous countries such as China, Brazil, and, to a lesser extent, India. As only a few countries currently have surplus protein to export, the projected increase in its demand is likely to pose serious challenges to these countries and to the world in general.

In overall world protein nutrition, milk products, representing about 10% of all protein consumption, are the third most important source of protein after cereals (40%) and meat (18%) (data for 2016 from FAOSTAT). When the low levels of lysine in cereals are taken into account (about one-third of that in dairy products), it is clear that milk protein plays a very important nutritional role in the world today.

The global dairy food scene: An overview

Milk and other dairy products have always been among the major everyday food items in human consumption in many cultures. It is a particularly useful food for the large, and possibly growing, number of vegetarians and flexitarians around the world. Its value for both infants and the elderly is easily recognized. Apart from its consumption in liquid form, there are many other ways in which milk is transformed and consumed. Innovations to make new milk-based products available in the market keep occurring.

With the growing world population and changing food habits, the production and the consumption of milk and other milk-based products have also been increasing over time. Over the five decades since 1961, world milk production more than doubled from 3.4 million tonnes to 7 million tonnes in 2009 (FAOSTAT) and 9.7 million tonnes in 2017 (IDF, 2018). Of this, 7 million tonnes or 82% is cows’ milk, with the rest from buffalo, goat, sheep, and camel.

The pattern of the regional production of cows’ milk (IDF, 2018) reveals that, as of 2017, Asia's share is the highest—with 30% of global production; Europe comes next, with 32%, followed by North America with 18%, South America with 9%, Africa with 5%, and Oceania with 4.5%.

It is important to note that much of the milk produced is consumed in the country (or economic bloc, in the case of the EU) in which it is produced and that just over 11% of dairy production is involved in international trade (2017 figures; IDF, 2018). In this context, it is noted that about 50% of whole milk powder, 49% of skim milk powder, and only about 12% of cheese are traded internationally (IDF, 2018). In 2017, the major exporters of cheese were the EU-27, the United States, New Zealand, Belarus, and Australia, and the main importers were Russia, Japan, the United States, Saudi Arabia, Korea, Mexico, Australia, and China (IDF, 2018). There is, evidently, some intraindustry trade in cheese. Given its variety and established regional specialties, this is not difficult to understand.

Five major exporters account for nearly 80% of world dairy trade in cows’ milk (IDF, 2018). In 2017, they were New Zealand (26%), the EU-28 (24%), the United States (14%), and Australia and Belarus (5% each). All of the exported milk consists of processed products, of which the main protein-containing products (in order of importance) are whole milk powder, skimmed milk powder, and cheese. Different countries dominate the export markets of these products (Table 1.3).

Table 1.3

a Excludes other products such as casein, whey products, and liquid and condensed milks. Values are based on protein of whole milk powder 25%, skim milk powder 35%, and cheese 25%. The cheese value is based on the bulk of traded cheese being cheddar.

Data from IDF, 2018. World Dairy Situation 2018. Bulletin of the International Dairy Federation 494/2018. International Dairy Federation, Brussels, Belgium.

One notable feature of the discussion earlier is perhaps the absence of the poorer developing countries among the major exporters and importers of such processed high value milk products as butter and cheese. One explanation for this may be that the consumption of these products is income sensitive. In some of these countries (e.g., Algeria and Mexico), the major purchase of dairy imports is by the government as part of a cost-effective strategy to support good nutrition.

This presumption is further confirmed when the trade patterns with respect to milk powders are examined. Milk powders are usually reconstituted for consumption as liquid milk and the demand for them is likely to be less income sensitive. Among the major importers of whole milk powder are China, Algeria, Saudi Arabia, Sri Lanka, and Nigeria; the major exporters are New Zealand, the EU-28, and Uruguay. For skimmed milk powder, the major importing countries are Mexico, China, Indonesia, Algeria, and the Philippines, and the major exporters are the EU-28, the United States, New Zealand, and Australia.

Whereas China features as a milk importer, India, perhaps surprisingly, is neither a major importer nor a major exporter of dairy products, although it has the largest bovine herd in the world. With the introduction around the mid-1960s of a system of dairy cooperatives under the umbrella of the National Dairy Development Board (NDDB), India's dairy industry has achieved a remarkable transition. Set up in 1965, the NDDB oversaw the dairy cooperatives collecting the often-small marketable surplus milk from the small herds scattered around the villages and supplying the growing market for milk in the urban areas. This linking of the milk producers with the markets—both groups being scattered in locations and large in numbers—generated a fivefold growth in India's milk production in three decades from the late 1960s, as domestic consumption of milk also rose steadily (Chatterjee, 1990; Brown, 2009). This transformation is all the more remarkable in that India's dairy industry is built almost entirely on crop residues—wheat or rice straw, corn stalks, vegetable residues, and grass gathered from the roadside—a rather different protein production model.

Although the consumption of dairy products is projected to grow as the standards of living improve in the developing world, some new developments, so far mainly in the more affluent countries, have also been creating additional demand for certain types of foods that are referred to as specialty foods. These include functional foods, defined as food and drink products making a specific health claim, organic foods, and genetically modified foods. Although international trade in specialty foods is still relatively small and confined to a few countries, evidence suggests that it is growing rapidly (Chatterjee, 2012). Dairy products feature prominently among both functional foods and organic foods that are currently traded internationally; other animal protein products feature less. The market for these products is likely to grow over time as the rising affluence spreads globally. Resources, including land devoted to mostly export-oriented organic farming, for example, have also been growing, particularly in the developing countries of Asia, Africa, and Latin America.

Conclusions

World hunger continues to be a major problem, although some of the drivers have changed, particularly the effects of climatic events and of conflict. Hunger has several dimensions, notably the need first and foremost for an adequate intake of calories; a close second is the need for adequate intakes of protein and of dietary essential amino acids. Protein nutrition is more complex than calories because all proteins are not equal: nutritional value depends on the type of protein and how it has been treated prior to consumption, as much as the amount of protein itself. Milk protein is a very high-quality protein, with a good supply of the dietary essential amino acids and high bioavailability. It can therefore be used to supplement poorer plant-derived proteins, such as cereal protein, to greatly improve the nutritional value of the combination. Milk production is growing globally, and the amounts of dairy products (and implicitly milk protein) traded internationally are also growing. Milk protein already accounts for 10% of the global food protein supply and makes a disproportionate contribution to global protein nutrition, based on its bioavailability and desirable composition. The future role of milk proteins in the global food protein economy continues to deserve special attention.

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Chapter 2

Milk proteins: An overview

D.A. Goulding; P.F. Fox; J.A. O’Mahony    School of Food and Nutritional Sciences, University College Cork, Cork, Ireland

Abstract

Proteins represent one of milk's macroconstituents (along with water, lipids, and carbohydrates), accounting for ~ 3.0%–3.5% of the total composition. In bovine milk, there are two main protein families, namely, casein and whey protein. Caseins are milk-specific proteins that exist as colloidal aggregates dispersed in milk serum. The bovine milk protein system is casein dominant, which enables large quantities of calcium to be delivered to the neonate. The natural function of milk is to supply the neonate of the species with its complete nutritional requirements for a period of time postpartum. Milk proteins (and their peptides) provide essential amino acids and amino groups for the biosynthesis of nonessential amino acids and, when in excess, also supply energy. They also provide many of milk's physiological functions, performed by immunoglobulins, enzymes, enzyme inhibitors, growth factors, hormones, and antibacterial agents. The development of advanced fractionation and processing techniques has led to the production of many milk-derived ingredients that have different functional properties and applications.

Keywords

Milk protein; Protein chemistry; Protein analysis; Protein ingredients

Introduction

Milk is a fluid that is secreted by the female of all mammals, of which there are about 4500 extant species (about 80% of mammalian species are extinct), primarily to meet the complete nutritional requirements of the neonate. The proteins of milk are essential in meeting many of the neonate's nutritional requirements as they provide essential amino acids and amino groups for the biosynthesis of nonessential amino acids. Milk proteins and peptides, including immunoglobulins, enzymes, enzyme inhibitors, growth factors, hormones, and antibacterial agents, also perform most of milk's physiological functions. The other requirements are for energy (supplied by lipids and lactose and, when in excess, by proteins), essential fatty acids, vitamins, inorganic elements, and water. Because the nutritional requirements of the neonate depend on its maturity at birth, its growth rate, and its energy requirements (which depend mainly on environmental temperature), the gross composition of milk shows large interspecies differences, which reflect these requirements (see Fox and McSweeney, 1998; Fuquay et al., 2011; McSweeney and Fox, 2013; Fox et al., 2015).

Although milk is designed to be species specific, humans have consumed the milk of other mammalian species for at least 8000 years (Kindstedt, 2012). World milk production has increased rapidly in recent decades, rising from 500 million tons in 1983 to 811 million tons in 2017 (FAO, 2018). Assuming an average protein content of ~ 3.5%, this equates to ~ 28 million tons of milk protein. The world's largest milk producers are India and the EU with ~ 20% of global production each, followed by the United States, China, Pakistan, and Brazil. Dairy is an integral part of the human diet in many parts of the world, with more than 6 billion people worldwide consuming milk and milk products; the majority of these people live in developing countries (FAO, 2018).

Of the milk constituents, the protein fraction represents the most value-added component. This is primarily due to an increasing acceptance that bovine milk proteins have superior nutritional and functional attributes compared with many other protein sources. Consequently, many types of milk protein ingredients are produced globally to satisfy market demands for a variety of industrial applications. The various milk protein ingredient types differ in nutrient composition, protein profile, and functional properties, facilitating a diverse range of industrial applications. The demand for milk protein ingredients will probably continue into the future because of constant developments in global socioeconomic conditions and large increases in world population (Lagrange et al., 2015). By 2050, the FAO predicts that the world's population will increase to 9.8 billion (United Nations, 2017). This increase in population will be coupled with the need for a 70% increase in food production to meet the added nutritional demands of the global population (Lagrange et al., 2015). The latest OECD/FAO report projects a 22% increase in global milk production by 2027, compared with the 2015–17 period, with most of that growth being in developing countries (OECD/FAO, 2018).

The chemistry and the physicochemical properties of milk have been studied for about 200 years and are now understood in considerable detail, as described in a voluminous literature. This chapter aims to provide an overview of milk proteins. The main chemical and physicochemical properties of the individual proteins are documented, followed by a summary of the analytical methods used to study milk proteins and an overview of the various milk protein ingredients available commercially throughout the world. Numerous textbooks and review articles are cited to assist the reader in identifying further reading material.

Bovine milk composition

Milk is a very complex fluid containing several hundred molecular species (several thousand, if all triglycerides are counted individually). The principal constituents are water, lipids, sugar (lactose), and proteins. In addition, there are numerous minor constituents, mostly at trace levels (e.g., minerals, vitamins, hormones, enzymes, and miscellaneous compounds). Reflecting mainly the nutritional and physiological requirements of the neonate, the composition of milk and even the profile of the constituents therein change markedly during lactation. The changes are most marked during the first few days postpartum, especially in the immunoglobulin fraction of proteins. The composition of milk remains relatively constant during midlactation but changes considerably in late lactation, reflecting the involution of the mammary gland tissue and the greater influx of blood constituents. The main constituents of bovine milk and their relative concentrations are listed in Table 2.1. The nonprotein constituents of milk are summarized here, and the protein system of