PH and NaCl effects on the interactions between safranal and whey protein isolate

Abstract

The molecular binding between whey protein isolate (WPI) and safranal, as a function of pH (4–9) and NaCl concentration (0–0.5 M), was studied using headspace solid phase micro-extraction coupled with gas chromatography (HS-SPME/GC) and fluorescence spectroscopy. Structural changes of WPI were also investigated using 3D-fluorescence and circular dichroism spectroscopies. Elucidation of the binding properties of WPI and safranal using HS-SPME/GC showed that pH 9 and 0.5 M NaCl favored the binding constant (Ka) being equal to 2.3 × 103 and 2.3 × 103 M−1, respectively. In addition, WPI had a single class of binding site for safranal with all conditions, except at pH 5 with two classes of binding sites. Structural studies of WPI using dynamic light scattering and atomic force microscopy showed its aggregation at pH 4, which could be a consequence of associations of whey proteins. WPI had looser secondary and tertiary structures with acidic (pH 4 and 5) and basic (pH 9) conditions compared with pH 7.2 and 6; as well as at 0.1 and 0.3 M NaCl compared with other NaCl concentrations. Both the secondary and tertiary structures of WPI were affected by complexation with safranal, with various solvent conditions. WPI could be introduced as a promising safranal carrier in dairy products with different pH and ionic strengths.