Structural, functional, and anti-cancer properties of conjugates of quinoa protein isolate and olive leaf polyphenolic extract: Application in production of bread

Plant-based proteins are of growing interest in the food industry as an alternative to replace animal based ones, however, their functional properties are limited and research is needed in order to improve emulsifying, foaming, solubility properties. The objectives of the present study were to investigate the impacts of complexation between quinoa protein isolate (QPI) and different concentrations of olive leaf polyphenolic extract (OLE) (0.1 %, 0.2 %, 0.3 %, 0.4 %, and 0.5 %) on the structural changes, functional properties, and in-vitro gastric digestion of QPI. The cytotoxicity of the hydrolyzed QPI/OLE complex, in which proteins turn to bioactive peptides, was evaluated using human stomach cancer cell lines. Additionally, bread using optimum QPI/OLE complex was produced and textural, sensorial, and color properties were evaluated. Fluorescence quenching and surface hydrophobicity measurements showed that QPI and OLE were complexed mainly through hydrophobic interactions. SDS-PAGE revealed that the complexation between the protein and phenolic compounds was appropriate and also complexes were highly digestible in stomach-like conditions. Additionally, OLE could enhance solubility, foaming as well as emulsification properties of QPI significantly. The rate of lipid hydroperoxide formation in QPI/OLE samples containing greater amounts of OLE was also reduced significantly. QPI/OLE complexes also exhibited a large potential to scavenge free radicals. In-vitro digestion experiment showed that the addition of OLE to the QPI solution promoted the production of bioactive peptides. According to the anti-cancer results, hydrolyzed QPI/OLE complexes exhibited a greater cell survival reduction in comparison to the OLE alone. Analysis of produced bread also revealed that the hardness of samples decreased with addition of QPI/OLE complexes. This study demonstrated that QPI/OLE complex shows the potential to be developed by food industry as a tailor-made functional food with health benefits.