Polyphenols as enhancers of emulsifying and antioxidant properties of egg and yeast protein emulsions: Understanding the molecular interactions behind their technological and functional potential

The rising interest in alternative protein sources, such as yeast protein extracts (YPEs), has recently brought attention to their interactions with polyphenols, which can enhance their structural and technological properties while providing health-beneficial properties, such as antioxidant activity. In this study, a multi-technique approach was employed to investigate the effects of a green tea extract (GTE), rich in flavanols, and a blueberry extract (BE), rich in anthocyanins, on the conformational and functional properties of enolase (ENO), the most abundant protein in YPE, and ovalbumin (OVA), representing chicken egg proteins. Overall, results highlighted the formation of non-covalent complexes with higher affinity under acidic conditions (pH 3.5). UV–vis and fluorescence quenching analyses revealed that ENO formed stronger molecular interactions with the extracts than OVA. FTIR spectroscopy showed a decrease in α-helices and a concurrent increase in random coil structures of ENO, with BE inducing greater protein unfolding and structural disorganization than GTE. In addition, 3D fluorescence spectra also highlighted conformational changes in BE structure upon binding with ENO. Electrochemical analysis proved that both GTE and BE antioxidant moieties were partially embedded within the protein structure, preserving their antioxidant capacity. The ENO emulsification activity index remained consistent after the addition of polyphenols, while its emulsion stability improved in the presence of BE (+48 %). The findings in this study suggest that ENO-polyphenol complexes have the potential to be applied as novel functional food ingredients.