Comparative study of the composition and thermal properties of protein isolates prepared from nine Phaseolus vulgaris legume varieties

Abstract Beans contain high amounts of protein and, as demonstrated with other legumes, may contain peptides with bioactive properties. Dozens of dry bean ( Phaseolus vulgaris ) varieties are grown in Canada, and many vary not only in terms of their protein content but also in their composition. In this study, the composition, molecular structure, and thermal properties of nine varieties of P. vulgaris were studied using electrophoresis, reversed-phase high-performance liquid chromatography (RP-HPLC), differential scanning calorimetry (DSC), and Fourier-transform infrared spectroscopy (FTIR). The predominant protein observed in each variety was vicilin. RP-HPLC chromatogram showed protein isolates (PIs) of white, great northern and black beans to have different profiles of low-molecular-weight proteins. Additionally, black bean PIs were missing proteins in the molecular mass (MM) range of 60 to 97 kDa. DSC analysis showed cranberry and light red kidney bean PIs to have significantly lower denaturation temperatures compared to the other varieties. RP-HPLC chromatograms of cranberry and light red kidney bean PIs were also very different. FTIR spectroscopy showed the predominant secondary structures in all varieties to be β-sheets and random coils. Increasing the temperature from 25 °C to 95 °C resulted in a reduction in β-sheet structures and an increase in the content of random coils and antiparallel β-sheet structures. Overall there were no major dissimilarities observed in the FTIR profiles of the nine P. vulgaris varieties.