Interaction Mechanism between α-Lactalbumin and Caffeic Acid: A Multispectroscopic and Molecular Docking Study

Caffeic acid (CA) is a phenolic acid found in a variety of foods. In this study, the interaction mechanism between α-lactalbumin (ALA) and CA was explored with the use of spectroscopic and computational techniques. The Stern-Volmer quenching constant data suggest a static mode of quenching between CA and ALA, depicting a gradual decrease in quenching constants with temperature rise. The binding constant, Gibbs free energy, enthalpy, and entropy values at 288, 298, and 310 K were calculated, and the obtained values suggest that the reaction is spontaneous and exothermic. Both in vitro and in silico studies show that hydrogen bonding is the dominant force in the CA-ALA interaction. Ser112 and Lys108 of ALA are predicted to form three hydrogen bonds with CA. The UV-visible spectroscopy measurements demonstrated that the absorbance peak A_280nm increased after addition of CA due to conformational change. The secondary structure of ALA was also slightly modified due to CA interaction. The circular dichroism (CD) studies showed that ALA gains more α-helical structure in response to increasing concentration of CA. The surface hydrophobicity of ALA is not changed in the presence of ethanol and CA. The present findings shown herein are helpful in understanding the binding mechanism of CA with whey proteins for the dairy processing industry and food nutrition security.