Determining the accuracy of colorimetric pH testing compared to potentiometric methods

Abstract

Background: Bacterial growth in foods can be prevented by applying various controls to the food product, including adjusting the acidity of the food. Research has indicated that a pH level of 4.6 or lower will be effective to prevent most bacterial growth. In order to verify this level has been achieved pH test strips (colorimetric) or a digital calibrated pH meter (potentiometric) can be used. This study attempted to quantify the degree of accuracy that pH test strips have compared to the calibrated pH meter. Method: MColorpHastTM pH indicator strips with a pH range of 0-14 were tested against a calibrated Extech pH100 meter. In this study 40 samples of rice were acidified to varying levels. Each sample was measured with both colorimetric and potentiometric method. Results were compared to determine the level of accuracy of the pH test strips. As well, test strips were used to measure pH in a variety of different coloured preserves. Results: A two-tailed test showed that there was a statistically significant difference between the readings from the pH test strips and the digital pH meter (P=0.0003). Conclusion: Based on the results, it can be concluded that both methods of measurement are not equally accurate. A calibrated pH meter will give more accurate readings of pH levels and should be used in most cases to confirm food safety with a high degree of confidence. In testing dark coloured jellies and preserves, pH test strips should not be relied on as they will be stained by the food, making the colorimetric reading difficult to determine accurately.