Effect of carboxymethylcellulose on the affinity between lysozyme and liposome monolayers: evidence for its bacteriostatic mechanism

Lysozyme (Ly), as an important natural preservative, easily interacts with anionic polysaccharides in food, which results in low and unstable bacteriostatic activity. The interaction of carboxymethylcellulose (CMC) with Ly was used to investigate the mechanism of the bioactivity changes caused by Ly binding polysaccharides. The affinity of Ly or Ly-CMC complexes for a mixed monolayer liposome (Lip) as an in vitro biomembrane model was characterized by using dynamic light scattering, Fourier transform infrared spectroscopy, circular dichroism spectroscopy, fluorescence analysis and interface activity measurements. The results showed that the affinity between Ly and Lip mainly depended on hydrophobic and electrostatic forces. The electrostatic interaction in Ly-CMC weakened the Ly-Lip affinity and altered the spatial conformation of Ly molecules. Furthermore, CMC screened the active sites of Ly and neutralized the charge of Ly, which may reduce its bioactivity. The presence of CMC decreased the increase in surface pressure in the Lip-Ly interface, which means that Ly-CMC has a lower insertion capacity and ability to induce lipid molecule rearrangement than Ly alone, indicating an inferior bacteriostatic ability. Our work explains how the bacteriostatic mechanism of Ly is affected by food biopolymers.