2.3.4 Foaming properties
The foaming properties were determined according to Stone et al.(2015). In brief, a 1.0% (w/w) protein solution (corrected by protein content) was prepared at pH 3, 5, and 7 and stirred overnight at 4℃. For each protein solution, 15 mL (V li) was transferred into a 400 mL tall glass beaker (inner diameter = 69 mm; height = 127 mm; as measured with a digital caliper) and foamed using an Omni Macro homogenizer (Omni International, Marietta, GA, USA) with a 20 mm saw tooth generating probe for a total of 5 min at speed 4 (~7,200 rpm). The foam was immediately transferred to a 50- or 100-mL graduated cylinder (inner diameter = 26 mm) after homogenization. The foam volume was recorded at time zero (V fi) and after 30 min (V ft) at room temperature. The foaming capacity (FC) and foaming stability (FS) were determined using following the equations:
\(\%FC=\frac{V_{\text{fi}}}{V_{\text{li}}}\times 100\%\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (3)\)
\(\%FS=\frac{V_{\text{ft}}}{V_{\text{fi}}}\times 100\%\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (4)\)
where Vfi is the volume of foam immediately after homogenization, and Vft is the volume of foam remaining after 30 min.
2.3.5 Statistical analysis
All protein products were prepared in triplicate on separate fermented meals (n=3). The results were reported as mean ± one standard deviation. A two-way analysis of variance (ANOVA) was used to study the statistical differences in protein functionality using a Tukey’s test with a significance level of p <0.05. A simple Pearson correlation (r ) was used to describe the relationship between the functional properties. The statistical analysis was performed using the IBM SPSS Version 28.0 software (IBM Corp. NY, IL, USA).