Functionalization of lupin (Lupinus luteus) protein isolate by means of high hydrostatic pressure

Lupin has gained great interest as an alternative source of proteins for the obtainment of protein isolates (PI) and development of plant-based meat analogues, due to its protein content, nutritional value, and sustainability. Food industry requires different PI with different techno-functional properties. Lupin PI presented relatively poor gelling properties limiting its application in the development of gelled meat analogues. The importance of PI in providing desirable properties and texture has led to the application of various modification techniques, such as high hydrostatic pressure (HHP), which can improve their techno-functionality.
Therefore, this study aimed to evaluate the effects of HHP treatment (200, 350, and 500 MPa for 10 min at 20°C) on the structure, and functional properties of LPI. HHP treatments resulted in structural changes, confirmed by gel electrophoresis which showed that increased levels of pressure induced the formation of high molecular weight protein aggregates.
The fluorescence intensity reduction, mainly at 350 and 500 MPa, indicated gradual unfolding of the protein with exposure of hydrophobic groups to hydrophilic environment.  Moreover, surface hydrophobicity was increased with increasing pressure, indicating a higher degree of unfolding whereas the free sulfhydryl content decreased with pressure. These changes help to explain the observed increase in solubility and decrease in emulsifying capacity. However, HHP treatment did not seem to affect the foaming properties. Additionally, the functionalization of the isolates by means of HHP led to improvement of the gelling capacity, since the least gelation concentration of the heat-induced gels decreased from 13% (control LPI) to 11% for the LPI that was treated at 200 and 350 MPa.
Overall, these results suggest that HHP could be applied to modify the protein structure and tailor the properties of PI, indicating that lupin protein might be a potential protein resource as a gelling agent in food matrices.