Influence of the method of protein extraction on the in-vitro evaluation of mineral dialysability from legumes

Abstract

The aim of this study was to investigate to what extent the in-vitro evaluation of iron, zinc and protein dialysability from legumes is influenced by the method of globulins extraction (G1, G2). According to classical methods, globulins were first extracted into salt solutions containing ascorbic acid. Because of the enhancing effect of ascorbic acid on iron availability, globulins extraction was also carried out in the absence of ascorbic acid. In the presence of ascorbic acid, a parallel reduction in total protein content and in iron and zinc content was detected, suggesting an interaction between minerals and protein components. Ascorbic acid markedly improved protein dialysability and G2 always showed a higher dialysability than G1. In the absence of ascorbic acid, iron dialysability was 3.0% from G1 and 5.5% from G2, while ascorbic acid caused up to a three-fold increase in iron dialysability. Ascorbic acid did not influence zinc dialysability (20% for G1 and 24% for G2). For both globulins, the higher the iron/protein ratio the higher the iron dialysability, indicating that the extent of interaction between iron and protein, as well as influencing protein digestion, likely affects in-vitro iron availability.