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

Abstract

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 ( T 20-130 • 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 • C) and −1.27 ± 0.1 ( T 20-130 • 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 • C) as well as commercial and self-made baby food (−0.56 ± 0.05, T 20-130 • C) is of special interest for the food industry to get a deeper insight in occurring reactions during thermal preservation processes.

Thermal inactivation of Bacillus cereus spores in micellar casein concentrates–effect of protein content and pH development

“…The slopes of the pH decrease over temperature were not significantly different (P≥0.05) for all the media examined except for whole milk against MCC with 3.3% protein. Walstra (2006) The decrease of the pH of milk, milk concentrates, and casein solutions with increasing temperature was already described in literature (Anema 2009;Chaplin and Lyster 1988;Reineke et al 2011) and the slopes were in the same range as the slopes observed in this study. The decrease of pH in milk and milk concentrate was attributed to the changing dissociation of ions and the supersaturation of calcium phosphate (Anema 2009;Walstra et al 2006).…”

“…It changes with increasing temperature. The pH value during heating can increase, decrease, or stay constant, depending on the buffer system (Reineke et al 2011). The pH development influences the heat resistance of spores.…”

“…The pH development influences the heat resistance of spores. It was shown that spores suspended in buffers having the same initial pH but a different pH development during heating do not exhibit the same inactivation behavior (Mathys et al 2008;Reineke et al 2011). Therefore, the heating media were further characterized regarding the buffering capacity as well as the pH development during heating at different protein contents.…”

“…The pH values of both milk and liquid MCC are in the neutral range (Beliciu et al 2012;Walstra et al 2006). During heating, the pH value of milk and milk concentrates decreases (Anema 2009;Reineke et al 2011;Walstra et al 2006) due to changing dissociation constants, the precipitation of calcium phosphate and the simultaneous formation of H + (Walstra et al 2006). The inactivation of spores is influenced by this pH development during heating depending on the properties of the buffer system of the heating medium (Mathys et al 2008;Reineke et al 2011).…”

“…During heating, the pH value of milk and milk concentrates decreases (Anema 2009;Reineke et al 2011;Walstra et al 2006) due to changing dissociation constants, the precipitation of calcium phosphate and the simultaneous formation of H + (Walstra et al 2006). The inactivation of spores is influenced by this pH development during heating depending on the properties of the buffer system of the heating medium (Mathys et al 2008;Reineke et al 2011). In milk concentrates with high micellar casein concentration such as MCC, the buffering capacity is enhanced because of the high amount of caseins (Salaün et al 2005;Wolfschoon-Pombo et al 2012).…”