Milk is a perfect beverage for all ages due to its high nutritious value. However, no one likes to drink a glass of spoiled milk for breakfast, not even accidentally! The bad taste is definitely a reason, but it is mainly because consuming spoiled or contaminated milk can also cause severe health issues.

To keep milk fresh and healthy for consumption, it is crucial to keep a close eye on its pH values. pH, which stands for 'potential of hydrogen,' is a measure of acidity or alkalinity and is a crucial factor in maintaining milk quality. The pH value of fresh raw milk is between 6.4 and 6.8, making it slightly acidic. A deviation from these values is quite noticeable in its taste and flavor. Over time, excess lactic acid can cause the pH value to change, making the milk smelly and sour in taste — far from being desirable.

So, how do we keep it fresh and healthy for consumption? By keeping a close eye on its pH values! pH, which stands for the potential of hydrogen, is a measure of acidity or alkalinity and is one crucial factor in maintaining milk quality. The pH value of fresh raw milk is between 6.4 and 6.8, which is slightly acidic. A deviation from these values is quite noticeable in its taste and flavor. This value changes over time due to excess lactic acid that makes it smelly and sour in taste, far from being preferred.

Importance of measuring pH in dairy samples

Dairy product manufacturers must maintain and monitor the pH values of milk as they play a vital role in achieving the desired characteristics of the products. For instance, the hardness and softness of cheese are determined by its pH. The milk cream is maintained at a particular pH in butter manufacturing to generate sweet butter. For sour butter, this cream is acidified further to a pH of 4.6 to 5.0 range. Lower pH values in dairy products also enhance their shelf life.

Not only that, the pH range of milk can also help detect signs of infections in lactating cattle, allowing for prompt intervention. The sterilization process is faster when the pH is lower. Hence, pH is an important quality parameter in the dairy industry, be it during packaging for human consumption or further processing for other dairy products.

Measurement of pH

pH is measured using a pH meter comprising an electrode and a meter. Conventional pH sensors face several challenges when it comes to measuring the pH of milk samples. The high protein and fat content of milk can cause precipitation and junction clogging in conventional pH sensors. Moreover, inefficient cleaning of sensors can lead to fouling of the pH membrane, resulting in a sluggish response. These pain points can hamper routine pH measurements and result in inaccurate and fluctuating pH readings. Therefore, selecting the sensors that are easy to clean, require low maintenance, and are robust to use is important.

Various other factors, including the calibration, temperature, cleanliness and storage of the sensors, also impact the accuracy of the pH measurements. Calibration, for example, is one of the most essential requirements for accurate readings. A two-point calibration (pH 4.01 and pH 7.00) is recommended for milk samples. While calibrating, one must handle buffers carefully and avoid any contamination.

Similarly, temperature must be constant while measuring the samples. Most of the pH meters these days automatically compensate for this. However, paying attention to this before starting the measurements is important. A pH sensor with an integrated temperature probe and Intelligent Sensor Management feature allows users to accurately capture critical parameters like calibration history.

Tips for maintaining dairy sample electrodes

  • If there is excessive clogging at the junction of the pH sensor, soak the sensor in a pepsin/HCl solution for one hour. It is ideal for removing protein contamination. Rinse and then recalibrate the sensor.
  • Clean the electrode regularly to remove accumulated fat and protein using deionized water, followed by ethanol, and finally again with deionized water.
  • Do not leave milk samples to dry over the sensor; this will clog the junction, making it difficult to clean and might damage the pH-sensitive glass membrane.
  • Maintain calibration buffers, samples and sensors at the same temperature for accurate pH measurement.
  • For quick and consistent measurement, ensure that the junction of the pH sensor is completely immersed in the sample.

Mettler Toledo offers an application note on “pH measurement in milk samples,” providing step-by-step guidance for pH analysis in dairy. Download to learn more. You can also visit their website for the right pH tool for your applications.

To contact the author of this article, email pHmatters@mt.com