Genetic reduction of antinutrients in common bean (Phaseolus vulgaris L.) seed, increases nutrients and in vitro iron bioavailability without depressing main agronomic traits

In common bean, lectins, phytic acid, polyphenols and tannins exert major antinutritional effects when grains are consumed as a staple food. Reduced iron and zinc absorption, low protein digestibility and high toxicity at the intestinal level are the causes of their antinutritional effect. To improve grain nutritional characteristics, the “low phytic acid” (lpa) trait recently obtained in bean and carried by the bean mutant lpa-280-10, was introgressed into different lectin-free (lf) lines, a few of which were white-seeded. The “white seed coat” (wsc) trait is correlated with a reduced amount of tannins and polyphenols in bean seed, and thus higher Fe bioavailability. Lf + lpa bean lines producing colored and white seeds, were developed. Three of these lines were submitted to a first field performance test carried out in two Italian locations, and two of them to biochemical analyses that evaluated fourteen nutritional parameters. Seedling emergence and grain yield of lf + lpa beans were statistically comparable to those of wild type cultivars, confirming the absence of major agronomic defects associated with the lpa trait. The presence of the three genetic traits lf, lpa and wsc in the same genetic background leads to a significant increase of the content of important nutrients such as crude proteins, total zinc, free phosphorus, and, in part, total iron. Iron bioavailability (as measured in vitro via a Caco-2 cell model) in lf + lpa brown and black seeds, was not significantly different from that surveyed in the wild type colored parents, while, it was on average twelve times higher in lf + lpa white bean seeds. Up to now, the white-seeded lf + lpa beans seem thus to be the only materials having really improved nutritional qualities.