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

Figures & data

Figure 1 (a) Calculated increase of pressure inside the measurement cell as filling volume increases for a temperature increase of ΔT 20–130°C. (b) Temperature profile for UHT-Milk measured inside the treatment chamber (fixed silicon oil temperature of 140°C) (color figure available online).

Figure 2 (a) Measured slope shift in a certified temperature-stable standard buffer solution versus 99.7% of Nernst-slope up to 100°C^[20], data up to 130°C were extrapolated. (b) Linear function of the electrode response from 20°C to 120°C in correlation with pH (color figure available online).

Figure 3 (a) pH shift in PBS buffer solution (0.05 M) and certified reference buffer-solution; (b) pH shift in ACES- (0.05 M) and TRIS buffer solution (0.05 M); C) pH shift in acetate- (0.05 M) and citrate buffer solution (0.05 M). Error bars indicate the standard error (color figure available online).

Figure 4 Thermal inactivation of Bacillus subtilis spores at 100°C in PBS and ACES buffer with an initial pH of 7 (0.05 M) at 20°C. Error bars indicate the standard error (color figure available online).

Table 1 pK_A values and standard molar enthalpies (Δ _r H ⁰) at 25°C^[17]

Buffer system	pKAat 25°C	Δ r H ^0[kJ mol-1]
TRIS	8.07	+47.4
ACES	6.84	+30.4
PBS (2nd)	7.19	+03.6
Citrate (2nd)	4.76	+02.2
Acetate	4.75	−00.4

Figure 5 (a) pH shift in raw milk and ultra heat treated milk (UHT-Milk) as well as; (b) pH shift in raw milk and its components (whey protein, casein and lactose [4.5%]) in dependence of temperature. Error bars indicate the standard error (color figure available online).

Figure 6 pH shift in commercial canned baby food versus pH shift in fresh prepared baby food by increase in temperature. Error bars indicate the standard error (color figure available online).