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°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°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 (ΔT 20–130°C) in the most commonly used buffer solutions and some selected food matrices. The ΔpH of certain buffer solutions, namely TRIS and ACES, showed a significant pH decrease of −2.01 ± 0.08 (ΔT 20–130°C) and −1.27 ± 0.1 (ΔT 20–130°C), respectively, whereas the pH of PBS buffer solution was nearly independent of temperature. The ΔpH decrease recorded in milk (−0.89 ± 0.6, ΔT 20–130°C) as well as commercial and self-made baby food (−0.56 ± 0.05, ΔT 20–130°C) is of special interest for the food industry to get a deeper insight in occurring reactions during thermal preservation processes.