Effect of trans-cinnamaldehyde or citral on sodium caseinate: Interfacial rheology and fluorescence quenching...

The interactions between sodium caseinate (CAS) and two natural aldehydes (trans-cinnamaldehyde (TC) and citral) were studied by evaluating oil/water (O/W) interfacial and fluorescence quenching properties. A small amount of TC in the oily phase resulted in lower O/W interfacial tension (9.12 mN/m). Particularly, the use of TC developed a stronger interface with higher elastic moduli (∼16.21 mN/m). This was supported by the fluorescence measurements: the quenching effect of TC on CAS was more pronounced than that of citral. Kinetic analysis indicated that both dynamic and static quenching occurs. The large binding constant (1.78 × 10⁵ M^-1) at 25 °C suggests that TC has strong affinity for CAS. Meanwhile, this binding process seemed to be spontaneous and driven by hydrogen bond formation with unfavorable conformational changes. This work would provide guidance for using the binding properties of natural aldehydes to enhance the interfacial properties of proteins.