FACTORS AFFECTING IN VITRO RUMEN DIGESTION OF FABA BEAN CULTIVARS (Vicia faba L.)

Experiments were conducted investigating the in vitro dry matter digestibility of eight faba bean (Vicia faba L. var. Major and Vicia faba L. var. Minor) cultivars. The testa of the different cultivars had a tannin content of 0−6.4%. The effect of adding condensed tannins on in vitro dry matter digestibility and in vitro protein digestibility of faba bean protein concentrate was also examined. Whole bean in vitro dry matter digestibility was greater (P < 0.05) in tannin-free faba bean cultivars than in those containing tannin. When the cotyledons and testa of some of the cultivars were examined separately, this difference was shown to be largely due to the higher digestibility of testa from the tannin-free cultivar. Regression analysis indicated that the in vitro digestibility of the whole bean was related to both the tannin and lignin contents of the testa. Autoclaving various faba bean fractions decreased (P < 0.05) the in vitro dry matter digestibility of the protein concentrate, whole bean and cotyledons, but had no effect on the digestibility of testa and starch. Adding condensed tannins, isolated from faba bean testa (cv. Diana), to the in vitro fermentation media decreased (P < 0.05) the in vitro dry matter and protein digestibility of the faba bean concentrate. The added tannins may have exerted their effect by binding the substrate protein.