Tannins and Their Complex Interaction with Different Organic Nitrogen Compounds and Enzymes: Old Paradigms versus Recent Advances

Abstract

Tannins, an abundant group of plant secondary compounds, raise interest in different fields of science, owing to their unique chemical characteristics. In chemical ecology, tannins play a crucial role in plant defense against pathogens, herbivores, and changing environmental conditions. In the food industry and in medicine, tannins are important because of their proven positive effect on human health and disease treatment. Such wide interests fueled studies on tannin chemistry, especially on their flagship ability to precipitate proteins. In this Review, we expand the basic knowledge on tannin chemistry to the newest insights from the field. We focus especially on tannin reactions with different non-protein organic N compounds, as well as the complex interactions of tannins with enzymes, resulting in either an increase or decrease in enzyme activity.

Keywords: organic nitrogen compounds; tannin chemistry; tannin–enzyme interactions; tannin–non-protein interactions; tannin–protein interactions.

Figure 1

Structure of tannins. A) simple gallotannin, B) simple ellagitannin, C) basic unit of condensed tannins, and D) condensed tannin trimer. Modified from Ref. 6.

Figure 2

Influence of tannins on enzymatic activity of acid phosphatase: A) changes in enzymatic activity after addition of tannins in different concentrations, B) residual activity of enzymes after formation of complex with tannins, C) infrared spectra of enzyme secondary structure presented as a stacked plot of second derivative. Black lines represent enzyme without tannins and blue lines enzymes with low tannin concentrations. Red lines show enzymes with high tannin concentration. Spectra are smoothed by using eight points. Region of alfa‐helix marked in yellow. Modified from Ref. 42.