Milk Composition and Fortification: Nutritional Benefits Across Species

Co-author: Collins Lawrence Omogiade

Milk is a rich source of essential nutrients, including proteins, fats, vitamins, and minerals. The composition of milk varies across species, and fortification has played a key role in enhancing its nutritional value.

Milk Composition and Variations Across Species

Milk is typically a white liquid, but its appearance varies across species. For instance, buffalo milk appears creamy white, while reindeer milk has a bluish tint due to differences in fat and protein content (Elbagerma et al., 2014). The pH of milk ranges from 6.7 to 6.9, classifying it as slightly acidic. Notably, colostrum—the first milk produced postpartum—differs from mature milk in composition, containing higher levels of immunoglobulins (antibodies), proteins, and vitamins to support neonatal immunity (Uruakpa et al., 2002). Milk composition varies significantly across species, breeds, lactation stages, and diets, reflecting evolutionary adaptations to environmental and nutritional demands (Skibiel et al., 2013). These variations highlight the potential of non-cattle milk, such as goat, sheep, and camel milk, which are often considered more similar to human milk in terms of composition and digestibility. This makes them promising candidates for specialized nutritional products, particularly for infants, children, and the elderly (Roy et al., 2020).

Milk Composition and Biochemistry

The composition of milk is a key factor in its nutritional value (Figure 1). Milk comprises approximately 87% water and 13% total solids, including fat (3.7%), protein (3.4%), lactose (4.8%), and minerals (0.7%) (Månsson, 2008; Gadzama, 2017). The solid-not-fat (SNF) fraction, which includes proteins, lactose, and minerals, forms the basis for dairy processing into products like cheese and yogurt. Milkfat exists as emulsified globules surrounded by a phospholipid membrane, which prevents coalescence and influences texture and creaminess (Singh, 2006). 

Key Components of Milk

1. Water: As the primary constituent, water acts as a solvent for milk’s nutrients and influences its physical properties, such as viscosity and freezing point.
2. Milk fat: Milkfat exists as emulsified globules surrounded by a phospholipid membrane, which prevents coalescence (Singh, 2006). The size of these globules affects texture and creaminess, with smaller globules enhancing mouthfeel in products like ice cream (Michalski et al., 2004).
3. Milk Proteins: Milk proteins include caseins (80%) and whey proteins (20%). Caseins form micelles that bind calcium phosphate, enabling efficient nutrient delivery (Goff, 2010). Whey proteins, such as α-lactalbumin and β-lactoglobulin, remain soluble after casein removal and are valued for their high bioavailability (Lönnerdal, 2003).
4. Lactose: This disaccharide, unique to mammalian milk, influences milk’s osmotic balance (Figure 1).  Approximately 68% of humans experience lactose intolerance due to reduced lactase enzyme activity post-weaning (WHO, 2021).
5. Minerals and Vitamins: Milk is rich in calcium, potassium, and phosphorus, with a 250 mL serving providing 30% of the daily calcium requirement (Weaver et al., 2016). Fortification with vitamin D is common in commercial milk to enhance calcium absorption (FDA, 2020).

Figure 1. The nutritional composition of milk

Fortification of Milk: Enhancing Nutritional Value

The nutritional profile of milk makes it an ideal candidate for fortification, a strategy used to address nutrient deficiencies and enhance its functional properties. Fortified milk can provide additional vitamins and minerals, such as vitamin A, vitamin D, iron, and zinc, which are critical for public health, especially in developing countries. For example, vitamin D fortification enhances calcium absorption and supports bone health (Bailey et al., 2010), while iron fortification addresses iron deficiency anemia, a prevalent issue in many populations. These efforts have been shown to improve nutritional status and reduce the prevalence of micronutrient deficiencies, making fortified milk a valuable tool in global nutrition programs.

Comparative Composition of Cattle and Non-Cattle Milk

Milk from different species varies significantly in composition, with non-cattle milk like goat, sheep, and camel milk offering unique nutritional benefits (Table 1).

Protein Profiles

Non-cattle milk, such as goat and camel milk, have lower casein-to-whey protein ratios compared to cow milk, making them more digestible and suitable for individuals with cow milk protein allergy (Roy et al., 2020).

Fat Composition

Goat and sheep milk are rich in medium-chain triglycerides, which are more easily digested than the long-chain triglycerides found in cow milk (Roy et al., 2020).

Digestive Dynamics

Non-cattle milk form softer curds during gastric digestion, leading to faster nutrient delivery and better tolerance, particularly for infants and the elderly (Roy et al., 2020).

Adapted from Alhadrami et al. (2016)

Implications for Human Nutrition

The unique composition and digestive properties of non-cattle milk make them valuable for developing specialized nutritional products. Their softer curd formation and faster digestion rates may benefit infants, the elderly, and individuals with digestive disorders. Additionally, the hypoallergenic potential of certain non-cattle milk, such as camel milk, offers opportunities for addressing cow milk protein allergy.

Conclusion

Milk's diverse composition across species highlights its nutritional significance and adaptability. Fortification enhances its value, addressing nutrient deficiencies and improving public health. Non-cattle milk offer unique benefits, particularly for individuals with digestive concerns. As dairy science evolves, optimizing milk's nutritional potential will remain crucial for global nutrition.

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