Structural modifications of lupin protein isolate induced by high hydrostatic pressure and their impact on in vitro...

The rising demand for plant-based proteins has intensified efforts to enhance the digestibility and functionality of legume-derived protein ingredients. This study examined the effects of high hydrostatic pressure (HHP) on the structural properties and in vitro digestibility of lupin protein isolate (LPI). Dispersions of LPI at protein concentrations ranging from 5 to 20% (w/v) were subjected to treatment at pressures of 300 to 600 MPa for 3 to 9 min. Structural modifications were evaluated using FTIR-ATR spectroscopy, molecular weight distribution was determined through SDS-PAGE under both reducing and non-reducing conditions, and digestibility was analyzed utilizing an in vitro gastrointestinal model expressed as the degree of hydrolysis (DH). Functional properties were assessed through protein solubility and emulsifying capacity (EC) and stability (ES). The application of HHP induced pressure- and concentration-dependent structural alterations, with moderate pressures (300-400 MPa) facilitating partial unfolding, as evidenced by slight reductions in α-helix content and increases in β-sheet structures, particularly at lower concentrations (5-10%). These conformational modifications significantly improved the DH (p < 0.05), with the highest digestibility observed at 400 MPa. Conversely, higher pressures (≥500 MPa) promoted aggregation, as indicated by diffuse high-molecular-weight bands and increased structural rigidity, leading to diminished digestibility and functional properties. Increasing protein concentrations further constrained pressure-induced unfolding due to matrix densification and restricted molecular mobility. In general, moderate HHP treatments effectively enhance lupin protein digestibility and techno-functional properties through controlled structural modifications; however, excessive pressure and elevated protein concentrations favor aggregation and hinder enzymatic hydrolysis. These findings highlight the importance of optimizing HHP conditions to develop high-quality lupin protein ingredients for plant-based food systems.