Composition and Quality of Milk
Milk represents one of the most complex naturally organized food systems, in which chemical composition and quality are inseparably linked. Milk quality cannot be reduced to individual numerical indicators but must be considered as the result of interactions among the main components – water, fats, proteins, lactose, and minerals – as well as their physicochemical state and biological origin. This review article examines milk as an integrated biochemical system, analyzing its composition, the factors determining it, and contemporary concepts of quality in a scientific, technological, and analytical context.
Introduction
In scientific and technological practice, the concept of “milk quality” is frequently used but rarely defined unequivocally. This is due to the fact that milk is not a simple mixture of substances but a dynamic biological system whose composition and properties reflect the physiological state of the animal, the conditions of rearing, the method of milking, and subsequent handling.
From this perspective, milk quality cannot be assessed solely through fat or protein content. It includes the structural organization of components, their stability, biological activity, and suitability for processing. Examining composition and quality within a review article requires a systemic approach that integrates chemistry, biology, and technology.
Milk as a Multiphase System
Physicochemically, milk is a multiphase system in which true solutions, colloidal particles, and emulsions coexist. Water constitutes the continuous phase in which the remaining components are distributed. Lactose and part of the minerals are present as true solutions, proteins form a colloidal system, and fats are dispersed as an emulsion.
This complex organization underlies the unique properties of milk—its stability, white color, nutritional completeness, and technological flexibility. Any change in one component leads to cascade effects throughout the entire system, making quality evaluation essentially an integrative process.
Water – The Carrier Medium of the Milk System
Water constitutes the largest portion of milk and serves as the medium in which all physicochemical and biological interactions occur. It is not a passive component but actively participates in stabilizing protein structures, distributing minerals, and regulating osmotic pressure.
Milk quality is closely related to the state of the aqueous phase. Dilution with water, for example, not only reduces the concentration of total solids but also disrupts the established equilibrium among components, which can be detected through changes in freezing point, electrical conductivity, and the relative ratios of major constituents.
Milk Fat as a Quality and Economic Factor
Milk fat is a key component from both nutritional and technological perspectives. It determines the energy value, flavor, and creamy texture of milk. In raw milk, fat exists as a stabilized emulsion of fat globules whose membrane is biologically active and structurally integrated into the milk system.
Milk quality is often evaluated through the content and condition of milk fat. Deviations in fat percentage, disruption of fat globule structure, or changes in fatty acid profile may indicate physiological disorders, improper feeding, or intentional adulteration.
Protein Composition as a Structural and Functional Indicator
Milk proteins perform a dual role—nutritional and structural. Caseins form the colloidal framework of milk, while whey proteins contribute to biological value and system reactivity. The ratio between these protein fractions is relatively stable and serves as an indicator of naturalness.
From a quality standpoint, protein composition is crucial for the technological suitability of milk. Coagulation properties, fermentation behavior, and thermal stability are directly related to protein–mineral interactions. Disturbances in this balance often lead to defects in the final product.
Lactose as a Regulator of Stability and Fermentation
Lactose is the most stable component of milk and plays a central role in maintaining osmotic equilibrium. It determines the amount of water in milk and serves as the primary energy substrate for microbiological processes.
From an analytical perspective, the stability of lactose makes it a valuable quality marker. Deviations in its content are often associated with dilution or whey addition. Technologically, lactose governs fermentation and acidity development, which are critical for the quality of fermented dairy products.
Mineral Composition and Ionic Equilibrium
Mineral substances in milk constitute a small proportion of its mass but have disproportionately large significance for quality. Calcium and phosphorus stabilize protein structures, determine buffering capacity, and influence coagulation. Alkali minerals regulate osmotic pressure and electrical conductivity.
Milk quality depends less on the absolute mineral content than on the way minerals are integrated into the milk system. Heat treatment, physiological changes, and adulteration can rearrange mineral equilibrium without significantly altering total mineral content.
Biological and Physiological Factors Determining Composition
Milk composition and quality are strongly influenced by biological factors such as breed, stage of lactation, health status, and animal nutrition. These factors determine not only the quantities of individual components but also their structural state.
From this perspective, milk quality can be viewed as a biological imprint of the animal and the conditions under which it was produced.
Milk Quality – An Analytical and Conceptual Approach
Modern assessment of milk quality is increasingly less limited to individual indicators. Instead, a comprehensive analytical approach is applied, considering the relationships among components, physicochemical parameters, and their interdependence.
In this sense, milk quality is not merely compliance with standards but the degree of structural and functional integrity of the milk system.
Milk composition and quality are inseparably linked and must be considered within a systemic context. Milk is not simply a collection of water, fats, proteins, and sugars, but a highly organized biological matrix in which each component performs structural, regulatory, and functional roles.
Understanding milk quality as an integrative property rather than a set of individual indicators is essential for modern dairy science, technology, and analytical control. This approach enables a more accurate assessment of naturalness, technological suitability, and nutritional value of milk.
