Like other Vicia species, the seeds of Vicia faba contain numerous antinutritional factors, notably tannins, pyrimidine glycosides (vicine and convicine), protease inhibitors, lectins, and phytic acid.
Tannins
The seed teguments of faba beans contain variable amounts of tannins, especially condensed tannins (proanthocyanidins), depending on the variety: some varieties are tannin-free while other contain 0.5-1% DM condensed tannins. The flowers of tannin-rich cultivars grown in Europe display a large black spot on the petals, and are often coloured in pale pink, pink or red, while tannin-free cultivars have white flowers (Crépon et al., 2010). Tannin-rich faba beans were found to have lower in vitro digestibility (Bond, 1976) and lower in vivo digestibility in pigs and poultry, whereas tannin-free cultivars have higher protein and amino acid digestibilities (Grosjean et al., 2001; Gatel, 1994; Crépon et al., 2010). This effect has not been reported in rabbits (Lebas, 1981; Seroux, 1984).
Vicine and convicine
The cotyledons of faba beans contain high concentrations of vicine and convicine (up to 1% DM or more, Lattanzio et al., 1983). These are pyrimidine glycosides responsible for favism, an acute hemolytic disease resulting from oxidative damage in red blood cells that affects human populations suffering from glucose-6-phosphate dehydrogenase deficiency (Enneking, 1995). Vicine and convincine are not toxic per se but are hydrolysed by ß-glycosidase in the intestine into divicine and isouramil. Low vicine and convicine cultivars have been developed (Duc et al., 1999). Vicine and convicine were not shown to affect faba bean digestibility in pigs but they were reported to be responsible for lower egg weight in laying hens (Lessire et al., 2005; Grosjean et al., 2001; Gatta et al., 2013).
Protease inhibitors and lectins
Trypsin and chimotrypsin inhibitors and lectins are present in faba beans but their activities are low compared to other legume seeds (Thacker, 1990; Vidal Valverde et al., 1998). The trypsin inhibiting activity of faba beans seems similar to that of spring peas cultivars (Gatel, 1994).
Phytic acid
The phytic acid concentration of faba bean was reported to be in the range 0.2-0.7% DM and to be generally lower than that of the common bean (Phaseolus vulgaris, 0.5-1% DM) (Vasic et al., 2012).