Structure and Composition of Milk and Milk Products

Milk is a white liquid produced by the mammary glands of mammals to nourish their young, secreted naturally after parturition. It is a major source of dietary energy, protein, and fat, contributing on average 134 kcal of energy per capita per day, 8 g of protein per capita per day, and 7.3 g of fat per capita per day.

Milk can be fermented to produce products such as cheese and yoghurt, and is also used to make ice cream, butterfat, and other derivatives.

This article explores the milk and milk product class in detail, covering typical examples and their detailed nutrient composition.

Nutritional Significance of Milk

Milk provides approximately 3 percent of dietary energy supply in Asia and Africa, compared to 8–9 percent in Europe and Oceania; 6–7 percent of dietary protein supply in Asia and Africa, compared to 19 percent in Europe; and 6–8 percent of dietary fat supply in Asia and Africa, compared to 11–14 percent in Europe, Oceania, and America.

Water is the primary component in all milks, ranging from 68 percent in reindeer milk to 91 percent in donkey milk. The main carbohydrate, lactose, aids in the intestinal absorption of calcium, magnesium, and phosphorus, and the utilization of vitamin D.

Lactose also provides a ready energy source for neonates, contributing 30 percent of the energy in bovine milk, nearly 40 percent in human milk, and 53–66 percent in equine milks. The proximate composition of cow and goat milk

Proximate Composition of Cow and Goat Milk (per 100 g)

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Unfermented Milk Products

1. Liquid Milk and Skim Milk as Beverages

Liquid milk is the most widely available form for human consumption. Raw milk, collected directly from animals, is typically heat-treated through pasteurization to eliminate disease-causing microorganisms and extend shelf life.

Pasteurization involves heat-treating every particle of milk to ensure safety and prolonged storage. Skim milk, with as much fat removed as possible, contains approximately half the calories of whole milk, making it the preferred choice for adults, particularly those on strict low-fat diets.

2. Cream and Butter Production

1. i. Cream: Cream is the fatty portion of milk, separated from nonfat solids to produce products with fat content ranging from 10–50%. Its rich flavor makes it desirable for desserts, cakes, and some chocolate confectionery.
2. ii. Butter: Butter is a fatty product derived exclusively from milk, containing a minimum of 80 g fat, a maximum of 16 g water, and 2 g nonfat milk solids per 100 g.

Read Also: Major Genetic Differences between Tropical and Temperate Livestock Breeds

Fermented Milk Products

1. Yoghurt and Its Nutritional Benefits

Yoghurt is a milk product fermented by lactic acid bacteria, representing the most popular milk product worldwide. It is produced from preheated milk with added flavorings or colorants to enhance consumer appeal.

The health-promoting properties of yoghurt are widely recognized, offering a good source of micronutrients that improve diet quality and support metabolic well-being within a healthy, energy-balanced dietary pattern.

Yoghurt has a more concentrated micronutrient composition than milk and is significantly associated with lower levels of circulating triglycerides, glucose, systolic blood pressure, and insulin resistance.

2. Nono: Nigerian Indigenous Yoghurt

Nono is a spontaneously lactic acid-fermented milk originating from northern Nigeria. It is prepared by inoculating freshly drawn cow milk with a small amount of leftover nono as a starter, followed by fermentation for 24 hours at room temperature. During fermentation, some lactose is converted to lactic acid.

After fermentation, the milk butter is removed by churning, leaving nono as a delicious and refreshing beverage. The fermentation involves bacteria (e.g., Lactobacillus acidophilus, L. bulgaricus, Lactococcus cremoris, L. lactis, Streptococcus thermophilus, Leuconostoc species), yeast, and molds, with Saccharomyces species being prominent, each contributing to the characteristic flavor.

Nono has a sharp, yoghurt-like acid taste and is typically consumed with sugar and fura, a millet flour product compressed into balls and cooked for 20–40 minutes.

3. Cheese and Its Production

Cheese production is an art combining science and technology to transform milk into a highly nutritious food using selected microorganisms.

Milk is the primary raw material, and the main step, coagulation of the casein component, is achieved through one or a combination of the following methods:

1. Limited proteolysis using enzymes.
2. Acidification by adding acids or a starter culture.
3. Acidification combined with heating to about 90°C.
   Most cheeses are produced by enzymatic (rennet) coagulation, traditionally using rennet from the stomachs of young calves, kids, lambs, or buffalo.

4. Wara: Nigerian Indigenous Cheese

Wara is a Nigerian cheese-type product prepared by coagulating fresh cow milk with Calotropis procera (Sodom apple) leaf extract. It is manufactured using rudimentary equipment, often without starter cultures, and processing conditions are typically not standardized.

Wara production is widespread in Nigeria, and a similar cheese, Wogachi, is made in the northern provinces of Benin Republic. Wara is rich in protein, containing approximately 20% protein.

Nutritional Composition of Milk Products

Milk and milk products, such as yoghurt and cheese, provide significant amounts of essential nutrients, particularly protein and calcium. Milk can be consumed fresh, as skim milk, or as cream, and can be fermented to produce yoghurt or cheese.

In Nigeria, nono and wara are notable examples of fermented milk products, valued for their nutritional content and cultural significance.

This article has detailed the foods within the milk and milk product class, including fresh milk, skim milk, cream, yoghurt, cheese, and Nigerian specialties like nono and wara.

These products are excellent sources of high-quality protein and calcium, contributing significantly to dietary nutrition. Their diverse forms and processing methods enhance their versatility and appeal in various culinary and cultural contexts.

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