Effect of tannic acid on lysozyme activity through intermolecular noncovalent binding

Lysozyme (Ly) is a good natural food preservative. However, its enzyme activity is easily influenced by food components, such as tannins. However, the specific mechanism is still unknown. In this study, tannic acid (TA) was used as model tannin to bind with Ly. The interactional properties of Ly-TA complexes were characterized with intrinsic fluorescence intensity, fourier transform infrared spectroscopy, circular dichroism and dynamic light scattering. The enzyme activities of Ly were analyzed by the lysis rate of Micrococcus lysodeikticus . The results indicated that TA can bind well with Ly through hydrophobic, hydrogen and electrostatic interactions, which induced the unfolding of Ly molecule. Consequently, the enzyme activity of Ly was inhibited for conformational changes and masking its active sites by TA, as well as the enzyme stability further declined in pH changes, thermal treatments and high salt concentrations. Our findings shed some light on the possible explanation of negative effects from tannins on the activity of Ly in plant foods.