A novel method to evaluate the relative tannin-binding capacities of salivary proteins

Many herbivore species have a diet containing high proportions of polyphenolics, principally lignins and tannins; the latter reduce the conversion of ingested nutrients into biomass and exert systemic toxicity at high levels of intake. It has been proposed that tannin-binding proteins in the saliva might be responsible for minimizing these tannin-related effects by forming soluble protein-tannin complexes. We have developed a method that permits evaluation of the relative tannin-binding properties of salivary proteins at a pH of 8.0-8.5. It is aimed at facilitating both the identification of tannin-binding proteins and the investigation of their relative tannin binding. The principle of the assay is the inhibition of trypsin by tannins and the subsequent reversal of that inhibition when other tannin-binding proteins are added (indirect assay). The method is rapid; large sample numbers may be processed by virtue of its microtiterplate format.