Conventional and ultrasound-assisted extractions of protein from sacha inchi (Plukenetia volubilis) and their impact on the physicochemical and structural characteristics

• Sacha inchi cake protein extraction conditions were optimized by ultrasound assistance (SIUS). • SIUS protein was extracted in less time than that obtained by alkaline solubilization (SIC). • SIUS had a darker color, a narrower particle size distribution and greater denaturation than SIC. • Protein structural modifications were found in SIUS compared to SIC. This study aimed to evaluate the recovery of proteins from sacha inchi (SI) cake, using two methods: conventional extraction by alkaline solubilization (SIC, pH 10.5, time 60 min, solvent/sample ratio 40/1) and ultrasound-assisted method (SIUS), the latter undergoing optimization using response surface methodology. The protein powder concentrate obtained by SIUS reached a protein content of ∼ 72% (dry weight, DW), under the optimized conditions of amplitude: 48%, solvent/sample ratio: 50 mL/g and time: 19 min at pH 10.5, compared to that obtained using the conventional method with ∼77% (DW). The physicochemical and structural characteristics differentiate both protein concentrates, the SIUS protein presented a slightly darker color, a narrower size particle distribution, a higher specific surface area, and a manifest denaturation as evidenced by the thermal analysis, compared to that obtained for SIC protein. The structural modifications of the proteins were evaluated by FTIR and circular dichroism (CD) spectroscopy, FTIR showed that the total proteins in SIUS had a decrease in β-sheet and an increase in β-turn configuration, whereas the soluble proteins evaluated by CD presented a marked decrease in α-helix and an increase in random coil and β-sheet configurations. The results contribute to offering information for future applications for both protein concentrates from SI cake in the food sector.