Shift of pH-Value During Thermal Treatments in Buffer Solutions and Selected Foods

The pH value is one of the most important process parameters during thermal treatments, regardless if the medium is a simple buffer solution or a complex food matrix. When the temperature increases after an initial measurement of the pH at ambient temperature (25 degrees C), a significant pH shift could occur, which could produce incomparable results in different buffer solutions or lead to side reactions during food preservation. Consequently, a measurement cell was constructed to record online the pH-value and temperature up to 130 degrees C. By applying the Nernst equation, it was possible to exclude the temperature-dependent influence of the pH glass electrode on the total pH value. The pH shift was measured over a wide temperature range (T 20-130 degrees C) in the most commonly used buffer solutions and some selected food matrices. The pH of certain buffer solutions, namely TRIS and ACES, showed a significant pH decrease of -2.01 +/- 0.08 (T 20-130 degrees C) and -1.27 +/- 0.1 (T 20-130 degrees C), respectively, whereas the pH of PBS buffer solution was nearly independent of temperature. The pH decrease recorded in milk (-0.89 +/- 0.6, T 20-130 degrees C) as well as commercial and self-made baby food (-0.56 +/- 0.05, T 20-130 degrees C) is of special interest for the food industry to get a deeper insight in occurring reactions during thermal preservation processes.