Abstract

Plant protein isolates are increasingly used as sustainable ingredients, yet intrinsic protein quality varies across legumes and genotypes. This study evaluated the amino acid composition and in vitro digestibility of protein isolates from 20 Phaseolus vulgaris landraces, providing a systematic comparison of protein-quality variability within a single species. Protein isolates were produced by alkaline extraction-isoelectric precipitation and digested using the INFOGEST static gastrointestinal model. Amino acids in non-digested samples and in digestible (supernatant) and indigestible (pellet) fractions were quantified by HPLC. Digestible indispensable amino acid ratios (in vitro DIAAR) and scores (in vitro DIAAS) were calculated relative to the FAO reference pattern for young children. Protein yields, contents and recoveries were high. Amino acid profiles were rich in indispensable amino acids, particularly LEU and LYS, while CYS and MET were the lowest. Digestibility varied across amino acids and landrace, with the widest ranges observed for CYS and PRO. Sulfur-containing amino acids were consistently first-limiting, resulting in in vitro DIAAS values ranging from 13.1% to 36.2%, below the FAO cutoff for protein-quality claims. Azufrado and Burro Cafe showed higher digestibility, whereas Hallado and Palo were consistently the lowest. These findings provide baseline data to support formulation and breeding strategies.