FACTORS AFFECTING IN-VITRO FORMATION OF TANNIN-PROTEIN COMPLEXES

In interaction of condensed tannins from Desmodium intortum and Lotus pedunculatus and tannic acid (hydrolysable tannin) with salivary mucop roteins (from sheep and goats), plant leaf proteins and bovine serum a lbumin were evaluated. These studies were carried out over a pH range of 2.0-9.0 and different inorganic ion conditions to simulate conditio ns in which dietary proteins would interact with tannins in a ruminant digestive tract. Insoluble tannin-protein interactions were found at pH 4.5-5.5 for bovine serum albumin and 3.5-5.5 for plant leaf protein . The present study showed that pH alone was not the sole determinant for tannin-protein complex formation, since tannin-protein complexatio n was found in the pH range 6.0-6.5 when different inorganic ions were added to the solutions. Insoluble complexes were not formed with sali vary proteins, although precipitation by tannic acid was achieved at 5 degrees C. This suggests that tannins may form soluble rather than in soluble complexes with salivary proteins. It was concluded that purifi ed F1 leaf protein (the major protei occurring in leaf tissue) ought t o be used as the test protein for evaluating tannin-protein interactio ns for in vitro assay procedures. Using this method it was calculated that 27-43% and 19-40% of available plant protein may interact with co ndensed tannins from Desmodium intortum and Lotus pedunculatus, respec tively.