The effect of proanthocyanidin-rich hulls and proanthocyanidin extracts from bean (Vicia faba L.) hulls on nutrient digestibility and digestive enzyme activities in young chicks

Proanthocyanidins were prepared from three bean (Vicia faba L.) varieties by extracting hulls in aqueous acetone. The amounts of freeze-dried extracts recovered were 74, 89 and 97 g/kg hull for the varieties Brunette, Statissa and Minica respectively. Chicks (3 weeks old) were fed on a maize–soya-bean control diet or the same control diet substituted with either 30 g proanthocyanidin extracts/kg or 300 g proanthocyanidin-rich hulls/kg. Chicks were tube-fed diets twice daily for 4 d. Nutrient digestibilities were calculated from amounts present in diets and freeze-dried excreta with the aid of titanium dioxide as a marker. Enzyme activities were measured in digesta removed from the jejunum. Extracts of proanthocyanidins depressed the digestibility of protein by 34%, starch by 3% and had no effect on the digestibility of lipid. Proanthocyanidin-rich hulls depressed the digestibility of protein by 62%, starch by 6% and lipid by 4%. Digestive enzyme activities were depressed to the same extent by extracts and hulls, trypsin (EC 3.4.21.4) by 55 and 62%, α-amylase (EC 3.2.1.1) by 75 and 78% and lipase (EC 3.1.1.3) by 31 and 32% for proanthocyanidin-extract and proanthocyanidin-rich-hull diets respectively. The susceptibility of substrates as well as enzymes to the effects of proanthocyanidins is discussed.