A feeding experiment was conducted with growing male Wistar rats to determine the effects of extruded faba bean (Vicia faba) on in vivo and in vitro intestinal absorption of D-galactose. The extrusion process abolishes haemagglutinating activity, trypsin, chymotrypsin and α-amylase inhibitory activity (Gujska & Khan, 1990). Condensed tannins and phytic acid content were also reduced significantly after processing (Liener, 1994).

Rats were fed raw faba beans (RFB) or an extrusion diet (EFB). A significant (P < 0.05, Student’s paired t test) impairment in growth rate and a significant (P < 0.05) inhibition in vivo and in vitro of intestinal absorption of galactose were found in raw faba beans (RF)-fed rats compared with casein (C)-fed rats. Moreover, extruded faba bean (EFB)-fed rats showed a significant (P < 0.05) improvement in growth rate and a significant increase (P < 0.001) in the rate of in vivo and in vitro intestinal absorption of D-galactose compared with RF and RFB groups, respectively. Animals fed with extruded legume-based diets showed a marked decrease in growth and a reduced in vivo and in vitro intestinal absorption of D-galactose compared with C rats.

The raw faba bean diet produced a 59 % inhibition (P < 0.001, Student’s paired t test) of 2 mM D-galactose uptake by intestinal rings. But the same extruded blend only produced an 18 % inhibition (P < 0.001) of the sugar intestinal uptake. Both inhibitions were different (P < 0.01). The inhibition was not completely abolished by thermal processing, suggesting that the remaining antinutritional factors after extrusion could be responsible for the reported effects. Gross denaturing of the glycocalix and of the brush border of the epithelial intestinal cells or the formation of complexes between some of faba bean components and nutrients are some of the mechanisms proposed by different investigators to explain these inhibitory effects.

This work was supported partially by the Spanish DGICYT97-0675 project.