Functional Properties
Changes of water holding capacity (WHC) and oil holding capacity (OHC) were determined according to the methods described by Choe et al. with minor modifications [9]. The sample (1.0 g) was placed in pre-weighed 25 mL centrifuge tubes and dispersed in 10 mL of distilled water/soybean oil under magnetic stirring with occasional vortex agitations for 10 min at room temperature. Afterwards, the samples were centrifuged at 4000 × g for 15 min at ambient temperature. Then, the centrifuge tube containing sediment was weighed. The WHC or OHC was appraised as g water or oil per g dry sample, respectively.
The emulsifying capacity (EC) and emulsifying stability (ES) were evaluated according to the described method of Di et al. with small modifications [21]. Briefly, 5 mL of soybean oil and 5 mL of sample solution (80 mg mL-1) was mixed. Then the mixture was homogenized by a high-speed shearing blender (PT-10-35GT, BUCHI Labortechnik AG, Switzerland) at 10, 000 rpm for 2 min at room temperature and centrifuged at 3000 ×g for 5 min at room temperature. The emulsion formed was admitted to keep for some minutes until the emulsion layer was stable. EC was calculated as follows Di et al:21
\(\text{EC\ }\left(\%\right)=\frac{H_{2}}{H_{1}}\times 100\) (2)
Where H1 was the total height of liquid, cm; H2 was the height of the emulsified layer, cm.
The above emulsion was centrifuged again after heating at 80 °C for 30 min and then cooled at room temperature. ES was expressed by the following equation Di et al [21]:
\(\text{ES\ }\left(\%\right)=\frac{H_{4}}{H_{3}}\times 100\) (3)
Where H3 was the total height of the liquid after heating; cm; H4 was the height of emulsion layer after heating, cm.
The foaming capacity (FC) and foaming stability (FS) were evaluated according to the described method of Di et al. with small modifications [21]. Sample solutions were prepared at 10 mg mL-1and pH of the phosphate buffer was adjusted to 7.0. The solutions were whipped in graduated plastic tubes using a homogenizer (PT-10-35GT, BUCHI Labortechnik AG, Switzerland) at 10, 000 rpm for 3 min at room temperature. The volume was recorded before and after whipping. FC and FS were reported by the formula (4).
\(\text{FC\ }\left(\%\right)=\frac{V_{1}-V_{0}}{V_{0}}\times 100\)(4)
Where V0 represented the volume prior to homogenization, mL; V1 represented the volume after homogenization, mL.
Following, the determination of FS was performed by a similar procedure and the residual foam volume was measured after sample keeping for 30 min at ambient temperature. The formula (5) was applied to express the FS value.
\(\text{FS\ }\left(\%\right)=\frac{V_{3}-V_{0}}{V_{0}}\times 100\)(5)
Where V3 represented the residual volume after standing, mL.