Effects of roasting on structural features of legume proteins

Roasting may induce chemical and structural changes in plant proteins, directly influencing their quality and techno-functionalities. In this study peanut (Arachis hypogaea) and baru nut (Dipteryx alata) were subjected to different roasting intensities (100, 120, and 150 °C for 20 min); and the effects were monitored by evaluating the chemical composition, instrumental color, browning index, phytic acid concentration, and protein profile. Defatted flours were obtained by grinding the samples and defatting with hexane for 1 h at 40 °C. Protein content of whole flour remained stable (~28% in both samples), while after defatting it increased to ~50% and ~48% in roasted samples at 150 °C for peanut and baru nut, respectively. Moisture content significantly decreased with increasing roasting intensity, ranging from 5.5% to 1.7% in peanut and from 5.8% to 2.8% in baru nut. Protein concentrates were prepared from defatted flours by alkaline extraction followed by isoelectric precipitation at acidic pH. The measured protein extraction yields were 61.3%, 77.5%, 77.8%, and 61.0% for peanut; and 41.4%, 38.2%, 41.9%, and 31.4% for baru nut, regarding unroasted samples and those subjected to 100, 120, and 150 °C for 20 min, respectively. Protein concentrates displayed high protein concentration, up to ~88% (peanut) and ~85% (baru nut) for the concentrates obtained from samples roasted at 100 °C/20min. Instrumental color analysis revealed progressive darkening as the roasting intensity increased, due to the occurrence of Maillard reaction. Conversely, the phytic acid content decreased as roasting intensified, reaching 1.95 g/100 g and 1.21 g/100 g in peanut and baru nut protein concentrates obtained from samples roasted at 150 °C for 20 min, respectively. Regarding the protein profile, SDS-PAGE indicated the formation of high-molecular-weight bands, consistent with disulfide-stabilized oligomers, triggered by roasting. These results highlight the practical relevance of roasting as a potential tool to modulate the properties of protein-rich ingredients from legumes.