Effect of tannin source and pH on stability of tannin-protein complexes

Quebracho (Schinopsis quebracho-colorado Schlecht) is the most extensively tannin extract explored in order to improve the use of protein in ruminant feed. The rock rose (Cistus ladanifer L.) and the grape seed (Vitis vinifera L.) are alternative sources of condensed tannins (CT). The objective of this study was to evaluate the effect of pH on the stability of complexes formed between the rock rose tannins and grape seed and the protein and fiber of soybean meal and compare the results with those obtained with the quebracho tannin extract. The results obtained show that the rock rose and grape seed tannins, such as quebracho tannins, have the ability to bind to soybean meal protein at pH between 6 and 8, reducing the solubility of nitrogen. These complexes are dissociated at pH 2, releasing the protein. This binding pattern supports the concept of using these tannin sources in ruminant nutrition as additives to protect the protein feed from excessive rumen degradation. However it was observed differences among tannin sources. Rock rose and grape seed tannins seem be more effectives in reducing protein degradation in the rumen than quebracho tannins.