In vitro studies were carried out to determine the factors that affect formation and dissociation of the protein-tannin complex (PTC) under conditions simulating those found in the digestive tract of the ruminant. For this study purified condensed tannins (CT) from the following tropical plants were used: Acacia harpophylla, Acacia aneura, Acacia saligna, Acacia holosericea, Tipuana tipu, Albizia chinensis, Flemingia macrophylla, Grevilea robusta, Casuarina cristata, Casuarina cunninghamiana, Azadarachta, Leucaena leucocephala, Leucaena pallida and Leucaena diversifolia. English spinach was selected as the source of soluble protein and during the growing phase, the plants were exposed to a 14C-CO2 atmosphere for 48 h. Following exposure, the foliar protein ribulose 1,5 biphosphate carboxylase/oxygenase, (rubisco) was isolated. The radioactive labelled protein was incubated with the isolated samples of CT for 2h at 39°C. The mixtures were then centrifuged and the percentages of bound protein (precipitate) and unbound protein (fluid phase) were determined. Formation of the protein-tannin complex (PTC) occurred over a range of pH 3-7. Above this pH 7, no PTC was formed. To determine the effects of pH on the dissociation of the PTC, the precipitate was incubated with buffers over a range of pH 3-9. It was found that acidic or alkaline pH was responsible for only 8 and 14% of the dissociation of the PTC, respectively. However, addition of abomasal and intestinal fluid from both sheep or cattle increased dissociation of PTC to more than 60%. Further analysis showed that pepsin and trypsin are largely responsible for the dissociation which occurs with the abomasal and intestinal fluids respectively.
Proceedings of the New Zealand Society of Animal Production, Volume 57, , 116-119, 1997
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