pH influences the interfacial properties of blue whiting (M. poutassou) and whey protein hydrolysates determining the physical stability of fish oil-in-water emulsions

Abstract

This work investigates the influence of the interfacial properties of whey protein (WPH) and blue whiting protein (BPH) hydrolysates on the physical stability of fish oil-in-water emulsions stabilized with these hydrolysates at pH 2 or 8. Measurements of interfacial tension and dilatational rheology confirmed that pH is a key factor affecting these interfacial properties of WPH and BPH. WPH, when tested at 1 and 10 mg/mL, showed a higher interfacial activity at pH 8 when compared to pH 2 or to BPH at pH 8 or 2, despite having a lower protein content. Moreover, when tested at 0.1 and 1 mg/mL, the dilatational modulus of WPH was significantly higher at pH 8 than at pH 2. These findings correlate with the formation of smaller oil droplets and a more resistant interfacial peptide layer for WPH at pH 8, hence explaining the improved physical stability of the 5% fish oil-in-water emulsion stabilized with WPH at pH 8. BPH did not show significant differences in interfacial activity with pH but exhibited significantly higher dilatational elasticity and viscosity at pH 2 compared to pH 8 (when measured at 0.1 mg/mL and 0.01 or 0.1 Hz). This correlates with the formation of stable 5% fish oil-in-water emulsions with BPH at pH 2 but not at pH 8.