Functional properties and Angiotensin-I converting enzyme inhibitory activity of soy-whey proteins and fractions

Soy proteins when prepared to high purity can confer good functional properties and the whey by-product is a potential source for bioactivity. In this study, we determined the protein, moisture, fiber, solubility, foaming, emulsion properties, as well as Angiotensin-I converting enzyme (ACE-I) inhibitory activity of prepared soy-whey proteins and its fractions. The soy-whey proteins were fractionated into < 5, > 5, > 10, and > 50 kDa using ultrafiltration. The expanded AACC methods were used to determine protein, moisture, and fiber analyses of the whey and its fractions. Solubility method was conducted to determine the protein solubility profile of the soy-whey and its fractions at varying pHs. Turbidimetric method was used to evaluate emulsifying activity (EA) and emulsion stability (ES). There were significant differences observed in moisture, protein and salt contents between unfractionated, > 50 kDa and smaller sized fractions. No significant differences were observed with phytic acid and total dietary fiber contents among all samples. The unfractionated whey protein and > 50 kDa fraction showed better solubility than other fractions. Unfractionated whey protein had the highest foam capacity (42.7 mL) while the fraction > 5 kDa showed the greatest foaming stability (46 min). The highest emulsion activity (0.33 ± 0.1) and stability (825.1 ± 45.1) was obtained with the > 50 kDa fraction while the unfractionated whey protein had the highest ACE-I inhibition activity. The findings indicate that soy-whey protein fraction (> 50 kDa) had good solubility, emulsion activity and stability, while the unfractionated whey protein exhibited the strongest ACE-I inhibition percentage (19%).