Influence of protein components (G1, G2 and albumin) on Fe and Zn dialysability from bean (Phaseolus vulgarisL.)

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Abstract
The influence of bean proteins on in vitro Fe and Zn dialysability was studied. Albumin and globulins (G1, G2) from Phaseolus vulgaris were characterised by SDS-PAGE and disc electrophoresis. Fe and Zn dialysability from whole flour was 2.28 and 27.5% respectively. Among protein fractions, albumin showed the lowest mineral dialysability (0.4% for Fe, 2.5% for Zn) in spite of having the highest Fe and Zn content. Globulins (G1 and G2) differed mainly in Fe dialysability (2.99 and 5% respectively), while presenting a similar Zn dialysability (20.3 and 23.6% respectively). Protein dialysability from bean protein fractions showed the same trend observed for minerals (albumin < G1 < G2). Unlike the whole seed, in protein fractions protein and Fe solubility showed the same behaviour, i.e. rising in the pepsin phase of digestion and decreasing in the pancreatic phase. These differences suggest that the intermediate products of protein digestion are responsible for Fe binding and solubilisation from bean protein fractions. Peptides dialysed from whole flour contained a low amount of all amino acids. Among protein fractions, albumin showed the lowest percentage of amino acids dialysability. A high amount of cysteine was found in the dialysates from globulins. The differences in the quantities of amino acids dialysed from albumin and globulins confirm how important the composition of protein digestion products is for mineral availability.