pH of Milk and Milk Products

Smartphone-based determination of pH after reaction with a chemically bound pH indicator

Introduction

The pH value of milk and milk products is one important parameter when checking the quality of your milk. E.g., the pH value of fresh milk should lie between 6.6 - 6.8. A higher pH value indicates a mastitis infection in the cow and a pH of below 6.5 indicates towards acidification of the sample.¹

A quick and easy way to check the pH of milk and milk products is using test strips. In combination with your smartphone, you get fast, convenient, and precise results. This low-priced and easy-to-use analytical detection system provides reliable quantification of water, food & beverage samples in research, industries, environmental analyses, and diagnostics.

The following application note describes the determination of the pH value of milk and milk products using the MQuant^® pH test strips in combination with the MQuant^® StripScan App.

Experimental Method

Special indicator dyes that are covalently bound to the reagent papers, change their color depending on the pH value of the sample.

• Measuring range
  pH 0 – 14
• Sample material
  Milk and milk products

Reagents, Instruments and Materials

Reagents

• MQuant^® pH-indicator strips pH 0 - 14 Universal indicator (1.09535)

Accessories

• MQuant^® Card (provided with the test strip box)
• MQuant^® StripScan App (can be downloaded via Apple App Store or Google Play Store)

Sample preparation

The sample can be analyzed in its original form.

Sample analysis

For the analysis, follow the below steps:

1. Start the App.
2. Get your MQuant^® pH indicator test strip and the MQuant^® Card ready.
3. Dip the test strip into the undiluted sample (15 – 25 °C) for approx. 2 seconds, ensuring that the reaction zone is completely immersed.
4. Remove the strip from the sample and if necessary, quickly rinse the reaction zones with distilled water to remove adherent sample, e.g., if yogurt is used.
5. Shake off excess liquid from the strip and dry the backside of the strip using a paper towel.
6. Select the parameter pH (1.09535) in the app. Wait for 15 seconds, till the color of the pH strip completely develops (a countdown is displayed on the screen, which begins immediately after selecting the parameter pH).
7. Just before the end of the countdown, place the test strip on the MQuant^® Card.
8. After the waiting time has elapsed, place the MQuant^® Card with the test strip within the viewfinder on your phone screen, and align the camera along the reference points.
9. The picture is captured automatically by the camera of the smartphone.
10. The result is displayed on the screen.

Results

Comparison with visual evaluation, Reflectoquant^® pH test (1.16894), and pH electrode seen in Table 1.

Table 1.

* Results are based on the average of a 5-fold determination
** UHT – Ultra-High Temperature

Note: Result graduation provided by MQuant^® StripScan is identical with graduation on test strip package.

Sample	pH value
	StripScan*	Visual Readout*	Reflectoquant®*	pH Electrode
UHT** Milk 1.5 % fat	6.5	7-Jun	6.4	6.58
UHT Milk 3 % fat	6.5	7-Jun	6	6.62
Whey, tropical	3.5	4-Mar	3.3	3.6
Cream	6.1	6	5.4	6.83
Cream, lac.-free	5.9	7-Jun	5.4	6.86
Quark	4.2	5-Apr	4.3	4.39
Yogurt, natural (1.5%)	4.5	5-Apr	4.4	4.4
Yogurt, natural (0.1%)	4.5	5-Apr	4.3	4.3
Yogurt, strawberry	4	5-Apr	4	4.22
Yogurt, blueberry	4.1	5-Apr	4	4.14
Butter Milk, peach	4	5-Apr	4.1	4.27
Butter Milk, cherry	4	4	4	4.17
Yogurt Lassi, strawberry	4	4	3.5	3.92

Conclusion

The MQuant^® pH strip in combination with the MQuant^® StripScan app is a quick and easy way to analyze the pH-values of milk and milk products. The measured values are comparable to those measured with the Reflectoquant^® system and the pH electrode.

For more information

• MQuant^® pH Indicator Test Strips see SigmaAlrich.com/phtests
• MQuant^® StripScan see SigmaAldrich.com/mquant-stripscan
• Applications see SigmaAldrich.com/wfa-applications

References

1. Töpel A. 2016. Chemie und Physik der Milch. 4. Auflage: Behr' s GmbH.