Rediscover Dairy

Dairy Kids
Dairy Gives You Go

As one of the five core food groups, dairy foods have a key role in a balanced diet. Dairy foods are convenient and cost effective and naturally contain more than 10 essential nutrients, including calcium, vitamin A, vitamin B12, riboflavin, carbohydrates, protein, potassium, phosphorus, magnesium and zinc.1,2 As a result of new technologies in genetics, molecular biology and analytical chemistry, a number of milk constituents with physiological benefits beyond milk’s traditional package of nutrients are being recognized.3

Energy

The energy (kilojoule) content of milk and other dairy foods varies widely and depends mostly on the specific fat content. However, the addition of non-fat milk solids, sweeteners and other energy-yielding components to dairy foods contributes to the total energy provided by the selected food.5 Milk is considered to be a nutrient-dense food that provides a meaningful amount of nutrients relative to its energy content.6

Proteins

Cow’s milk protein is an important protein source in the diet owing to its high quality and biological value. It is a good source of essential (i.e. required for growth and which cannot be synthesized by the body) and branched-chain amino acids.7,8 Cow’s milk contains about 3.5% protein, of which 80% is casein and 20% is whey protein. Each of these proteins has unique amino acid profiles, characteristics and biological functions, including exerting antibacterial, antiviral, antifungal, opioid and immunomodulatory effects in addition to improving absorption of other nutrients.7

Carbohydrates

Lactose (B-D-galactopyranosyl-(1,4)-D-glucopyranose) is the principal carbohydrate in milk. It is more commonly known as ‘milk sugar’ and consists of a glucose and a galactose molecule bound together. Lactose varies slightly in concentration in milk (4.5-5.2 g/100 g) and exists as two forms (a and B), which differ in their solubility and sweetness (B-lactose is slightly sweeter than the a form). Lactose is also used as a fermentation substrate by lactic acid bacteria.4,9

Fats

Milk fat contributes unique characteristics to the appearance, texture, flavour and stability of dairy foods. It is the main source of energy in milk and provide essential vitamins and several other potential health-promoting components. The majority of the lipids in milk occur as fat globules, with 96-98% consisting of triglycerides. The rest is free fatty acids, cholesterol, diglycerides, monoglycerides and phospholipids.9 The composition of milk fat varies somewhat according to the animal origin, stage of lactation, presence of mastitis, ruminal fermentation or feed-related factors.

Typically, about 70% of the fat is in the form of saturated fatty acids (SFAs) and 30% exists as unsaturated fatty acids. Palmitic, myristic and stearic acid constitute 30%, 11% and 12% of the SFAs, respectively. Short-chain fatty acids make up 11% of SFAS. Oleic acid is the main monounsaturated fatty acid in milk (25-35%), with polyunsaturated fatty acids constituting only approximately 2% of the total fatty acid content.7

Current dietary recommendations advise moderation in total fat intake (20-35% of total energy value), with less than 10% of energy to be contributed by SFAs. Intake of trans fatty acids should be kept to a minimum. When selecting milk or milk products, low-fat or fat-free choices are recommended.

Vitamins

Almost all of the vitamins known to be essential to humans are found in milk, including the fat-soluble vitamins A, D and E, as well as the water-soluble B-complex vitamins and vitamin C. The fat content of milk determines the concentration of fat- soluble vitamins and therefore low-fat and skim milk varieties have lower amounts of these vitamins.7

Vitamin A has an important role in vision, gene expression, cellular differentiation, embryonic development, growth, reproduction and immunocompetence.2 Milk and milk products are an important dietary source of vitamin A.

Three servings of full-cream dairy, consisting of 250 ml milk, 200 ml yoghurt and 40 g cheese, will provide 29% and 36% of the RDA for vitamin A in adult men and women, respectively.10,11

Vitamin D, a fat-soluble vitamin that enhances the intestinal absorption of calcium and phosphorus, is essential for the maintenance of a healthy skeleton throughout life.2 As milk is not fortified in South Africa, vitamin D is present in low concentrations. However, exposure to sunlight should provide adequate vitamin D for most people living in South Africa.

Vitamin E is an antioxidant that protects cell membranes and lipoproteins from oxidative damage by free radicals. This vitamin helps to maintain cell membrane integrity and stimulates the immune response.2 Vitamin E is present in low concentrations in milk (109 μg/100 g).10 In addition to the essential fat-soluble vitamins, milk and other dairy foods contain all of the water-soluble vitamins required by humans in varying amounts. Significant amounts of thiamine (vitamin B1), which acts as a coenzyme for many reactions in carbohydrate metabolism, are found in milk. Three servings of dairy provide about 8% and 10% of the thiamine recommended for adult men and women, respectively.

Milk is also an excellent source of riboflavin (vitamin B2). This vitamin functions as a precursor for some of the essential coenzymes in the oxidation of glucose, fatty acids, amino acids and purines. The average riboflavin content of fluid full- cream milk is 0.158 mg/100 g.2,10,11

Niacin functions as part of a coenzyme involved in fat synthesis, tissue respiration and utilisation of carbohydrates. This vitamin promotes a healthy digestive tract, skin and nerves, as well as aiding in digestion and fostering a normal appetite. The niacin content of milk is 0.107 mg/100 g.2,10,11

Milk is also a good source of pantothenic acid, a component of coenzyme A, which is involved in fatty acid metabolism.

Folate as found in milk is a growth factor and functions as a coenzyme in the transfer of nucleotides necessary for DNA synthesis. Cow’s milk contains a high-affinity folate- binding protein, which is a minor whey protein that promotes retention and increases the bioavailabilty of folate by slowing the rate of its absorption. Adequate folate nutrition is especially important for women of childbearing age to reduce the risk of neural tube defects in infants.

Three servings of dairy will supply approximately 9% of the 400 μg folate recommended for adults per day.10,11

References

  1. International Dairy Federation. Health Professionals. IDF World Dairy Summit. Mexico, 2008.
  2. Whitney EN, Rolfe SR. Understanding nutrition. 14th ed. Stamford: Cengage Learning, 2016.
  3. German JB. Bioactive components in milk. Curr Opin Clin Nutr Metab Care. 2002; 5(6):653-658
  4. Chandan R. Dairy based ingredients. St Paul: Eagern Press, 1997.
  5. US Department of Agriculture. Agricultural Research Services. Nutrient Data laboratory.
  6. International Dairy Federation. Health Professionals. Final IDF position on general principles of nutrient profiling, 2008.
  7. Pereira PC. Milk nutritional composition and its role in human health. Nutrition. 2014; 30:619-627.
  8. Haug A, Høstmark AT, Harstad OM. Bovine milk in human nutrition – a review. Lipids Health Dis. 2007; 6:25.
  9. Mourad G, Bettache G, Samir M. Composition and nutritional value of raw milk. Issues Biol Sci Pharm Res. 2014; 2(10):115-122.
  10. Smit LE. Schönfeldt H. The nutritional content of South African milk and liquid milk products. Irene: Dairy Industry Centre, 1998.
  11. Institute of Medicine. Dietary reference intakes. Washington, DC: National Academies Press, 2012.

Leave a Comment

Your email address will not be published. Required fields are marked *


[vc_row][vc_column][vc_column_text]

Nutrient Components

As one of the core food groups, dairy plays a key role in a balanced diet. Dairy products are convenient, cost effective and tasty and naturally contain more than ten essential nutrients, including protein, carbohydrates, vitamin A, riboflavin, vitamin B12, calcium, potassium, phosphorus, magnesium and zinc. As a result of new technologies in genetics, molecular biology and analytical chemistry, a number of milk constituents with physiological benefits beyond milk’s traditional package of nutrients are being recognised. Milk is the primary ingredient of dairy products and the nutrients found in milk are therefore discussed first. Fresh, full­-cream cow’s milk is a liquid food (87.5% water) and it contains an average of 12.5% total solids of which 9% are non­fat solids. Refer to Figure 1 for a schematic diagram of the major components of milk.

imageEnergy

The energy (kilojoule) content of milk and other dairy products varies widely and depends mostly on the fat content of the product. However, the addition of non­fat milk solids, sweeteners and other energy­ yielding components to dairy products contributes to the total energy provided by the selected food. Milk is considered to be a nutrient ­rich food, providing a meaningful amount of nutrients relative to its energy content.

Protein

Cow’s milk is recognised as an excellent source of high ­quality protein. Cow’s milk contains about 3.25% protein, of which 82% is casein and 18% is whey protein. Each of these proteins have unique characteristics and biological functions. Whey protein concentrates and isolates are used as ingredients in a number of formulated food products.

Nutritionally, cow’s milk protein is considered to be a ‘complete protein’, because it contains, in varying amounts, all nine essential amino acids required for growth and which cannot be synthesised by the body.

Carbohydrates

Lactose, the principal carbohydrate in milk, is synthesised in a cow’s the mammary glands. Lactose accounts for approximately 54% of the total non­fat solids of milk and contributes about 30% of the energy of full­cream milk. Cow’s milk contains about 4.63% lactose, which translates to 12 g lactose per 250 ml.

Minor quantities of glucose, galactose and oligosaccharides are also present in milk. Glucose and galactose are the products of lactose hydrolysis by the enzyme lactase.

Fat

image Milk fat contributes unique characteristics to the appearance, texture, flavour, and stability of dairy products. It is a source of energy, essential fatty acids, fat­-soluble vitamins, and several other potential health promoting components.

Milk fat, the most complex of dietary fats, exists in microscopic globules in an oil-in-­water emulsion in milk. These fats are unique amongst animal fats, because it contains a relatively high proportion of short-­chain and medium­-chain saturated fatty acids.

The composition of milk fat varies somewhat according to the breed of the cow, stage of lactation, season, geographical location and feed composition.

In full­-cream milk, approximately 56% of the fat is in the form of saturated fatty acids, 25% is monounsaturated fatty acids, and 3% is polyunsaturated fatty acids.

Although saturated fatty acids generally contribute to an increase in blood cholesterol levels, individual saturated fatty acids differ in their blood cholesterol ­raising effects. Long-­chain saturated fatty acids, such as lauric, myristic and palmitic acids, raise total and low-­density lipoproteins (LDL) blood levels, whereas stearic acids and short-­chain saturated fatty acids, such as butyric, caproic, caprylic and capric acids have either a neutral effect or may lower blood cholesterol levels. Oleic acid is the main monounsaturated fatty acid in milk fat. Polyunsaturated fatty acids, such as arachidonic acid, are present in trace amounts.

Omega­3 ­linolenic acid and its products, eicosapentaenoic acid (EPA) and docosahexa­aenoic acid (DHA), are also present in small but significant amounts. Current dietary recommendations advise moderation in total fat intake (20–35% of total kilojoules), with less than 10% of kilojoules from saturated fatty acids, and keeping intake of trans fatty acids as low as possible.

Vitamins

Almost all of the vitamins known to be essential to humans are found in milk. Vitamin A, D, E and K are associated with the fat component of milk. Vitamin A plays an important role in vision, gene expression, cellular differentiation, embryonic development, growth, reproduction and immune competence.

Both vitamin A and its precursors – principally beta-­carotene – are present in variable amounts in milk fat.

Milk and milk products are an important dietary source of vitamin A. Three servings of full-­cream dairy consisting of 250 ml milk, 200 ml yoghurt and 40 g cheese will provide 29% and 36% of the RDA for vitamin A for adult males and females, respectively. Cow’s milk is a good source not only of vitamin A, but also of beta­ lacto-globulin, the major protein component of bovine milk whey, which may enhance vitamin A absorption.

Vitamin D, a fat-­soluble vitamin that enhances the intestinal absorption of calcium and phosphorus, is essential for the maintenance of a healthy skeleton throughout life. Vitamin D is present in low concentrations in South African milk as it is unfortified, but exposure to sunlight should provide adequate vitamin D for most people living in South Africa.

Vitamin E is an antioxidant, protecting cell membranes and lipoproteins from oxidative damage by free radicals. This vitamin helps to maintain cell membrane integrity and stimulate the immune response. Vitamin E is present in low concentrations in full-­cream milk (109 μg per 100 g).

In addition to the essential fat­-soluble vitamins, milk and other dairy products contain all of the water-­soluble vitamins in varying amounts required by humans. Thiamine (vitamin B1), which acts as a coenzyme for many reactions in carbohydrate metabolism, are found in milk. Three servings of dairy provide about 8% and 10% of the thiamine recommended for adult males and females, respectively. Milk is also an excellent source of riboflavin, or vitamin B2. This vitamin functions as a precursor for certain essential coenzymes important in the oxidation of glucose, fatty acids, amino acids and purines. The average riboflavin content of full­-cream milk is about 0.158 mg/100 g.

Niacin functions as part of a coenzyme in fat synthesis, tissue respiration and utilisation of carbohydrates. This vitamin promotes healthy skin, nerves and digestive tract, and aids digestion and the fostering of a normal appetite. The average amount of niacin in milk is 0.107 mg/100 g.

Milk is also a good source of pantothenic acid, a component of the coenzyme A involved in fatty acid metabolism. Folate, found in milk, is a growth factor and functions as a coenzyme in the transfer of nucleotides necessary for DNA synthesis. Cow’s milk contains a high-­affinity folate-­binding protein (FBP), a minor whey protein that promotes retention and increases the bio-availabilty of folate by slowing the rate of absorption.

Adequate folate nutrition is especially important for women of childbearing age and can reduce the risk of neural tube defects in infants. Three servings of dairy would supply approximately 9% of the 400μg folate recommended per day for adults.

Dairy is very high in vitamin B12, which is necessary for growth, maintenance of nerve tissue and normal blood formation. Milk provides 0.44 μg vitamin B12 per 100 g.

Minerals

Milk and other dairy products are a good source of readily bio-available calcium, providing approximately 300 mg per serving.

It is also an important source of other minerals, such as phosphorus, magnesium, potassium, and trace minerals such as zinc.

Phosphorus is an essential mineral that plays a central role in metabolism and is a component of lipids, proteins, and carbohydrate. Magnesium, a required cofactor for more than 300 enzyme systems in the body, is related to calcium and phosphorus function. This mineral activates many of the body’s enzymes, participates in the synthesis of protein from amino acids, and plays a role in the metabolism of carbohydrates  and fat. Because magnesium is widely distributed in foods, particularly those of vegetable origin, a deficiency of this nutrient is rare.

Potassium contributes to the transmission of nerve impulses and helps to control skeletal muscle contraction. Accumulating scientific evidence supports the beneficial role of potassium in blood pressure control as well as the prevention of hypertension. Milk contains about 157 mg potassium per 100 g and is ranked as the top food source of potassium.

imageMilk and other dairy products contain many trace elements or nutrients needed by the body at levels of only a few milligrams per day, such as zinc, selenium and iodine. Trace elements in cow’s milk are highly variable and depend on the stage of lactation, season, milk yield, the amount of trace elements in each cow’s diet, post-­pasteurisation handling of milk and storage conditions.

Zinc is essential for growth and development, wound healing, immunity, and other physiological processes. Zinc is also a regulator of gene expression and helps maintain the integrity of cell membranes. Dairy products such as milk, cheese, yoghurt and maas are a source of zinc.

Iodine, which is naturally present in milk, is an essential component of the thyroid hormones, which regulate growth and metabolism. The iodine content of cow’s milk varies widely, depending on the geographical area and iodine intake of the cow.

[su_spoiler title=”References” class=”my-custom-spoiler”]

1. International Dairy Federation. 2008. Health Professionals. IDF World Dairy Summit. Mexico. http//www.idfdairynutrition.org.

2. Whitney EN & Rolfes SR. 2002. Understanding Nutrition. 9th ed. Wadsworth. USA

3. Foote JA et al. 2004. J Nutr. 134: 1779­1785.

4. German JB. 2002. Curr Opn Clin Metab Care. 5: 653.

5. Miller GD et al. 2007. Handbook of dairy foods and nutrition.3rd ed. National Dairy Council. New York.

6. Chandan R. 1997. Dairy based ingredients. Eagern Press. StPaul.

7. US Department of Agriculture. Agricultural Research Services.Nutrient Data laboratory. http://www.ars.usda.gov/ba/bhnrc/ ndl.

8. International Dairy Federation. 2008. Health Professionals.Final IDF Position on general principles of nutrient profiling. http://www.idf.org.

9. International Dairy Federation. 1994. Milk protein definition &standardization. Brussels. Belgium.

10. Institute of Medicine of the National Academics. 2002. Dietary reference intakes for energy, carbohydrates , fibre, fat, fatty acids, cholesterol, protein and amino acids. The national academic press. Washington DC.

11. Phillips SM et al. 2009. J Am Coll Nutr. 28(4): 343–354.

12. Bos C et al. 2000. J Am Coll Nutr. 19(2): 191S–205S.

13. Fox PF. 1992. Advanced dietary chemistry. Vol 1. Proteins.Chapman & Hall. New York.

14. Suavez FL. 1997. Food Technology. 51: 74–76

15. Jensen RG. 1995. Handbook of milk composition.Academic press. New York.

16. Parodi PW et al. 2004. Australia J Dairy Technology.59(3): 3­59.

17. Lorenzen JK & Astrup A. 2011. Br J Nutr. 31: 1­10.

18. Schaafsma G. 2000. J Nutr. 130: 1865S–1867S.

19. Institute of Medicine of the National Academics. 2001. Dietary reference intakes for Vit A & Zinc.

20. Yetley EA et al. 2009. Am J Clin Nutr.89(3): 719–727.

21. Smit et al. 1998. The nutritional content of South African Milk and Liquid Milk Products. Dairy Industry Center. Irene.

22. Institute of Medicine. 1998. Dietary reference intakes for Thiamin, Riboflavin & Niacin. National Academic Press.

23. Miller GD et al. 2001. J Am Coll Nutr.20(2 suppl): 168S­185S.

24. Weaver CM & Heaney RP. 2006.Calcium in human health. Chapter 9, Food sources, supplements and bioavailability. p. 129­142. Humana Press. Totowa. NJ.

[/su_spoiler][/vc_column_text][/vc_column][/vc_row]

Leave a Reply

Your email address will not be published. Required fields are marked *


Scroll to Top
Rediscover Dairy