The amino acid absorption from legume protein isolates (from chickpeas, CPI; and lupins, LPI) was studied in in vivo and in vitro experiments in comparison to animal proteins (casein and lactalbumin). In the in vivo experiment on rats, the diets were isoenergetic and isonitrogen (per kg diet 15.5 MJ digestible energy and 150 g protein, respectively). At 150 min after feeding, the concentration of free amino acids in arterial and portal blood plasma of rats fed legume proteins was significantly different (p < 0.05) from rats fed animal protein (lactalbumin). In arterial plasma the concentration for Met, Leu, Trp and Lys in rats fed legume proteins was lower than lactalbumin controls and for Val and Cys higher; in portal plasma, the concentration of free Met, Leu, Trp and Lys was lower, and the concentration of Cys was higher in rats fed legume proteins than in rats fed lactalbumin. The cumulative (total mM at 195 min after ingestion) and net absorption (% of ingested amounts) of Met, Leu, Trp and Lys were higher (p < 0.01) for rats fed lactalbumin as compared to those fed legume protein isolates or casein. In the in vitro study (Caco-2 cell monolayers), after 2 h incubation the transport values of all the individual amino acids in CPI and LPI, except for Glu, Val and Ile, were lower (p < 0.01) than for casein or lactalbumin. The results indicate that amino acids from chickpea and lupin protein isolates are absorbed at slower rates than those from animal proteins, which might explain the lower nutritional utilisation of legume storage proteins as compared with lactalbumin or casein.
Keywords: Cicer arietinum; Lupinus angustifolius; absorption; amino acids; in vitro; protein isolates; rats.