What is the pH of milk?
In this brief article, we will provide you with the answer to the question: “What is the pH of milk?”, discuss what is pH and the benefits of cow’s milk consumption.
What is the pH of milk?
Bovine milk (excluding mastitis and colostrum) exhibits a pH range of 6.6 to 6.8. Additionally, various physicochemical properties of milk, such as rennetability, ethanol stability, and heat stability, undergo fluctuations throughout the lactation period. (1)
Bovine milk primarily comprises water, constituting approximately 87% (w/w) of its composition. This aqueous component contains dissolved and suspended elements, serving as a vital source of hydration and nutrient supply for the neonate.
The pH of milk is a dynamic parameter, subject to constant changes during milk processing. These fluctuations can be attributed to factors like temperature variations, pressure adjustments, alterations in dry matter content, water removal, or microbial activity. (2)
What is pH?
pH represents the concentration of H+ ions, denoted as [H+], in an aqueous solution through a logarithmic expression. It offers a convenient way to express a wide range of [H+] values using small positive numbers. The letter “p” is used to signify the negative logarithm to the base10.
The pH scale extends from 0 to 14, encompassing hydrogen ion concentrations found in both dilute aqueous solutions and biological systems. A pH of 7 is considered neutral, which is characteristic of pure water.
When the pH value is less than 7, it indicates acidity, while a pH value greater than 7 signifies alkalinity or basicity. Due to its logarithmic nature, a change of one pH unit represents a tenfold difference in hydrogen ion concentration. (3)
What are the components of milk?
The composition of milk is subject to various influences, including the species of the animal, lactation stage, and genetics. Additionally, environmental conditions and the provided diet can also bring about changes in milk composition.
On average, milk is primarily composed of approximately 87% water, 4%-5% lactose, 3% protein, 3%-4% fat, 0.8% minerals, and 0.1% vitamins. When comparing milk from different species, cow milk stands out with the lowest fat content, second only to human milk in protein content. (4)
What factors affect milk pH?
The pH of milk is predominantly influenced by its amino acid profile, temperature, and mineral composition. While other milk components, such as lactose, lactose breakdown products, and microorganisms, also have an impact on milk pH, they are often considered as secondary or external factors.
To assess the overall influence of the milk ecosystem on pH, examining its buffering capacity is a useful approach.
Although minerals constitute a relatively small fraction of milk when compared to fat, protein, lactose, and water, they play a crucial role in stabilizing and configuring casein micelles. Consequently, they significantly affect the physicochemical and functional properties of dairy products. (2)
What are the Effects of Solids Content and Temperature on Milk pH?
The removal of water from milk systems causes a higher ratio of solute to solvent, leading to an increase in the ionic strength of the solution. This elevated ionic strength directly affects the hydrogen ion activity and, consequently, the pH.
During the evaporation process, the pH of milk decreases, and the ionic strength increases, resulting in a reduction in the activity coefficient of soluble calcium and phosphate.
Additionally, heat treatment often accompanies evaporation simultaneously, adding further complexity to consider when measuring the pH of milk concentrates. Therefore, multiple factors need to be taken into account to accurately assess the pH in such situations.
As the temperature of milk rises, the soluble contents of both calcium and phosphate decrease, and hydrogen ions are released simultaneously, leading to a decrease in pH. (2)
Can pH be used as a measure of milk spoilage ?
Yes, the pH of fresh milk is approximately 6.7, creating an environment suitable for the growth of various bacteria.
In the pH range of 4.0 – 5.0, lactic acid bacteria can thrive and produce lactic acid.
While these bacteria play a positive role in inhibiting the growth of harmful pathogens and are intentionally used in fermenting milk to produce dairy products like yogurt and cheese, they can also contribute to undesirable spoilage in specific circumstances.
As milk spoils, its acidity increases, making acidity a measurable indicator of milk quality. (5)
What happens if you consume spoiled milk?
Consuming spoiled milk can lead to food poisoning, manifesting as symptoms such as nausea, vomiting, diarrhea, abdominal cramps, fever, weakness, headaches, and dehydration.
Typically, a mild food poisoning episode lasts for approximately one to two days, while a more severe case may persist for up to 10 days. If the symptoms worsen or if diarrhea and vomiting persist for more than three days, seeking medical assistance is advisable. (6, 7)
In this brief article, we provided you with the answer to the question: “What is the pH of milk?”, discussed what is pH and the benefits of cow’s milk consumption.
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- Aydogdu T, O’Mahony JA, McCarthy NA. pH, the Fundamentals for Milk and Dairy Processing: A Review. Dairy. 4(3):395-409. 2023.
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- Lu, M., & Wang, N. S. Spoilage of Milk and Dairy Products. The Microbiological Quality of Food, 151–178. 2017.
- Adda Bjarnadottir, Kelli McGrane, How Long Is Milk Good for After the Expiration Date? Them. Healthline Media LLC. 2020