Tannins digestive inhibitors

More complex, second order interactions may be imagined, involving more than one natural enemy. For example, consider insects to which tannins are important deterrents and digestion inhibitors. As mentioned above, elevated gut pH appears to be a way of dealing with tannins, since tannin-protein complexes are dissociated or inhibited at alkaline pH (16,32). Indeed, using a model in vitro system in which hemoglobin is employed as a protein substrate, we found that several natural tannins and phenolic extracts do not precipitate this protein when the pH exceeds about... 

Faba beans contain several ANFs such as tannins, protease inhibitors (vicin/ convicin) and lectins. Use of low-vicin/convicin cultivars may allow substantial levels of faba beans to be included in poultry diets (Danner, 2003). The levels of trypsin inhibitor and lectin activities are low compared with other legume seeds and do not pose problems in poultry diets when faba beans are incorporated into diets at the levels shown below. Of most concern for poultry is the tannin fraction, which has been shown to depress digestibility of the protein and AA (Ortiz et al., 1993). Tannins in whole faba beans are associated with the seedcoat (testa), and the tannin content is related to the colour of the seedcoat (and flowers). Tannins are lower in white than in the colour-seeded varieties. 

Some of the best investigated anti-nutrients are the enzyme inhibitors present in legumes and other plants. The Bowman-Birk and the Kunitz inhibitors of trypsin and other proteases are among the best characterized. In contrast to the non-specific and widespread influences of tannins and lectins (Carmona, 1996), the Bowman-Birk, Kunitz and other such inhibitors target specific enzymes. Corresponding with this, proteases and other digestive enzymes vary in sensitivity to the different inhibitors. 

Skills in separation of grain components and their analysis are needed to address these problems. Some examples of naturally occurring antinutritional compounds are phytates (already mentioned), phenols, tannins, and trypsin- and a-amylase inhibitors. Phenols and tannins bind with and precipitate proteins in food systems, thus decreasing digestibility. Minimizahon of these compounds in cereals is an objective. 

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