Modulation of antinutritional compounds in common bean seeds: exploitation of diversity and novel uses

Legume seeds are a good source of energy, dietary fiber, proteins, minerals and vitamins required for human health. An increasing number of studies has provided indications that consumption of legumes is associated with physiological and health benefits, such as prevention of cardiovascular disease, obesity, diabetes mellitus and cancer. The growing body of research on these health benefits has stimulated interest in developing innovative technologies to expand the use of pulses in food products. From a nutritional point of view, the amino acid profile of legume seed (storage) proteins reveals low amounts of the essential sulfur-containing amino acids (i.e. methionine and cysteine) and tryptophan, while lysine, another essential amino acid, is quite abundant. Legume proteins complement very well those of cereals, which are normally rich in sulfur amino acids and poor in lysine and threonine. However, legume seeds also contain many bioactive and/or antinutritional compounds, such as phytate, galactooligosaccharides, phenolic compounds, lectins, enzyme inhibitors, which presence could affect their nutritional value. In our laboratory we have developed genetic materials of common bean with different seed composition in terms of absence/presence of bioactive proteins (lectins and alfa amylase inhibitor) and phytic acid. With the perspective to promote and increase legume consumption we prepared six types of biscuits containing different amounts of bean flours (from 12 to 29%) in association with wheat and /or maize flours (from 10 to 29% and from 10 to 22%, respectively). The bean genotype we choose was the Lady Joy cv, lacking lectins, but still containing alpha-amylase inhibitor and phytic acid. The six different biscuit types were subjected to a sensory evaluation, bromatological analyses and total amino acid content. Consumer's acceptability decreased with increasing percentage of bean flour. Formulations with 12% and 14% of bean flour were moderately accepted by consumers, indicating that technological optimization is needed to meet sensory and hedonic expectations. Further results showed that the addition of bean flour improved total protein content, increased fiber content and balanced amino acid composition. Other two types of biscuits were then prepared using bean flours (14%) from the following genotypes: Taylor's Horticultural cv (with normal levels of lectins, alpha amylase inhibitor and phytic acid), a lpa1 mutant (devoid of lectins, alpha amylase inhibitor and with 90% reduction of phytic acid) and compared with biscuits prepared with Lady Joy bean flour. Analyses of biological activities of lectins, alpha amylase inhibitor and of phytic acid content showed that after backing there is still about 10% of lectin activity, while almost all (90%) of the alpha amylas inhibitor is still active. Finally when a lpa1 bean flour is used it contributes to a 35% decrease of total phytic acid.