3.8.3. Effect of pH on Foaming Capacity and Stability

Foam capacity (FC) and stability (FS) were measured according to the method of Jezowski et al. [ ˙ 71]. Briefly, one gram of the preparation was weighed into the tube and 200 mL of distilled water was added to it. The resulting mixture was adjusted to the appropriate pH (2, 4, 6, 8, 10 or 12) using 0.5 M NaOH or 0.5 HCl. The sample was then homogenized for 2 min at 16,000 rpm (T25 basic ULTRA-TURRAX®; IKA Werke, Staufen, Germany). The beaten sample was immediately transferred to a measuring cylinder, where the total foam volume was determined after 0, 5, 10, 30 and 60 min. FC and FS were calculated according to the following equations (Equations (2) and (3)):

$$\text{FC} = \frac{\text{VA}}{\text{VB}} \times 100 \, (\%) \tag{2}$$

where VA denotes the volume after whipping (mL), and VB is the volume before whipping (mL).

$$\text{FS} = \frac{\text{VB}}{\text{VT}} \times 100 \,\text{(\%)}\tag{3}$$

where VB denotes the volume before whipping (cm<sup>3</sup> ), and VT is the volume after a certain time (mL).
