Tannins in faba bean seeds: effects on the digestion of protein and amino acids in growing chicks

Abstract

Tannins from faba bean hulls were extracted with 70% aqueous acetone; after filtration and removal of some contaminants, the clear solution was lyophilized. The protein precipitation capacity of faba bean tannins was measured by the precipitation assay; the relationship between BSA precipitated ( y, mg) and condensed tannins ( x, mg) was: y = 0.367 + 1.538 x. Experimental diets based on 67.5% dehulled faba beans without or with supplemental freeze-dried tannin extract (0, 8, 16 and 24 g kg −1 diet) were given to 25-day-old chicks for 3 days, after which the chicks were killed and the digesta from the ileum collected. The addition of tannins to the basal diet significantly ( P < 0.01) reduced the protein digestibility from 88.8 to 80.8% and there was a high correlation between the level of tannins in the diet and digestibility values. Amino acid digestibility followed the pattern shown by the crude protein and the mean differences among treatments were in the range of 5.4–12.6%.