Calcium redistribution contributes to the hard-to-cook phenotype and increases PHA-L lectin thermal stability in common bean low phytic acid 1 mutant seeds

•Genetic reduction of phytic acid results in hard-to-cook phenotype in common bean seeds.•Cooking increases stability of PHA-L lectin in low phytic acid1 mutant.•Addition of a cation chelator during cooking reverses stability of PHA-L lectin.•Calcium redistribution occurs in black low phytic acid1 seeds.•Low phytic acid1 seeds contain fewer phytate globoids than wild type. Seed phytic acid reduces mineral bioavailability by chelating minerals. Consumption of common bean seeds with the low phytic acid 1 (lpa1) mutation improved iron status in human trials but caused adverse gastrointestinal effects, presumably due to increased stability of lectin phytohemagglutinin L (PHA-L) compared to the wild type (wt). A hard-to-cook (HTC) defect observed in lpa1 seeds intensified this problem. We quantified the HTC phenotype of lpa1 common beans with three genetic backgrounds. The HTC phenotype in the lpa1 black bean line correlated with the redistribution of calcium particularly in the cell walls, providing support for the “phytase-phytate-pectin” theory of the HTC mechanism. Furthermore, the excess of free cations in the lpa1 mutation in combination with different PHA alleles affected the stability of PHA-L lectin.