Fabrication of antioxidant emulsifiers from natural ingredients: Conjugation of egg white proteins with catechin and chlorogenic acid

Abstract

There is considerable interest in developing dual functionality ingredients for application within the food industry. In this study, catechin (CT) and chlorogenic acid (CA) were conjugated to egg white protein (EWP) by using a free radical method to create antioxidant emulsifiers. The CT and CA contents of the antioxidant emulsifiers were 2.76% and 7.13%, respectively, and CT and CA modification altered the isoelectric point value of EWP to a lower pH. Amino acid analysis showed that CT was primarily conjugated to EWP through Tyr, His, Lys, Arg, Cys, and Trp residues, whereas CA was conjugated through Cys, Tyr and Trp residues. Combined liquid chromatography and mass spectrometry had identified numerous cross-linking sites after trypsin, chymotrypsin, and Glu-C protease + trypsin digestion, and this finding was consistent with the amino acid analysis results. In addition, 63 oxidation sites were detected in ovalbumin, ovotransferrin, and lysozyme molecules. The antioxidant activities of EWP–CT and EWP–CA conjugates were 2.5- and 4.5- fold (2-diphenyl-1-picrylhydrazyl radical scavenging activities) 2.4- and 4.9- fold (ferric reducing powers) higher than those of the unmodified EWP, respectively. Confocal laser scanning fluorescence microscopy revealed that the aggregation stability of the emulsions was improved when CT or CA was conjugated to EWP. The improved emulsification properties are possibly attributed to a decrease in surface hydrophobicity. Our results show that effective antioxidant emulsifiers can be fabricated by conjugating polyphenols to EWP.