Extrusion increases in vitro bioaccessibility of mineral elements in pinto bean (Phaseolus Vulgaris L) flour
P. GULATI (1), F. Sumargo (2), M. Guttieri (2), S. Weier (2), D. Rose (2) (1) University of Nebraska-Lincoln, Lincoln, U.S.A.; (2) University of Nebraska-Lincoln, , U.S.A..
Pinto beans (<i>Phaseolus vulgaris</i>) are “good sources” (>10% of the US Daily Value per serving) of Fe, Mg, P, and K. However, previous reports have suggested low bioavailability, especially of the divalent cations, due to the chelating effects of phytic acid, tannins, and dietary fibers. Extrusion may be a strategy to improve the bioaccessibility of these elements. In this study, <i>in vitro </i>bioaccessibility of Fe, Mg, P, and K, as well as two heavy metals (Cd and Pb), were analyzed in unprocessed and extruded pinto bean flours. Physical properties (radial expansion, apparent bulk density, water solubility index and water absorption index) and chemical composition (dietary fiber, phytic acid, and tannins) were also determined. Extrusion parameters (temperature, moisture content, screw speed) significantly affected physical properties, but not element bioaccessibility or chemical properties, except in a few isolated cases. Extrusion did, however, increase the bioaccessibility of all essential elements (Fe, Mg, P, and K) by 1-5% without a comparable increased in toxic elements (<0.5% for Cd and Pb) compared to unprocessed flour. A significant reduction in phytic acid and tannins together with an increase in soluble dietary fiber was found after extrusion. Correlation analysis suggested that bioaccessibility of Fe is associated with phytic acid concentration, while Mg is associated with tannins and heavy metals are associated with soluble dietary fiber. The increase in element bioaccessibility by extrusion cooking is related to the changes in chemical components, whereas the severity of the extrusion process affected physical properties of pinto bean extrudates.
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