Synthesis, characterization, antioxidant and antimicrobial activities of starch aldehyde-quercetin conjugate

In this study, corn starch was functionalized with quercetin. Starch was first oxidized by sodium periodate to produce starch aldehyde, and then starch aldehyde was conjugated with quercetin through acid catalyzed condensation reaction. The structure, antioxidant and antimicrobial activities of starch aldehyde-quercetin conjugate were evaluated. Thin layer chromatography confirmed the conjugate did not contain free quercetin. The UV-vis spectrum of the conjugate exhibited an absorption band at 320 nm. Fourier-transform infrared and proton nuclear magnetic resonance spectra of the conjugate confirmed the aldehyde groups of starch aldehyde were involved in the conjugation reaction. X-ray diffraction pattern revealed the conjugate was in the amorphous state. Scanning electron microscopy observation showed the conjugate had sheet-like, virgate and round shapes. The structure of starch aldehyde-quercetin conjugate was different from that of native starch and starch aldehyde. As compared with native starch and starch aldehyde, starch aldehyde-quercetin conjugate exhibited higher reducing power, free radical scavenging activity and antimicrobial activity against Escherichia coli, Staphylococcus aureus, Salmonella and Listeria monocytogenes. Our results suggested starch aldehyde-quercetin conjugate could be developed as an antioxidant and antimicrobial agent in food industry.