Abstract
Honey is composed of macromolecules arranged into multicomponent colloidal particles dispersed in a supersaturated sugar solution. The core part of colloidal particles in honey is made up of high-molecular weight protein-polyphenol complexes. We designed a multi-step extraction process to gain better insight into the phenolic compounds strongly bound to proteins in honey. Honeys were sequentially extracted by solvents of reduced polarities and the extraction process was monitored by LC-ESI-MS/MS. Unexpectedly, the results revealed ubiquinone-like compounds that partitioned to both, soluble supernatants and protein-bound insoluble residues from which they were released after the pronase-digestion of proteins. The accurate mass measurement and MS/MS fragmentation patterns using UPHLC-MS/MS coupled to quadrupole orbitrap confirmed their identification as ubiquinones. Distribution of ubiquinone-bound proteins was further investigated by the fractionation of honey protein-polyphenol complexes by size-exclusion chromatography followed by LC-ESI-MS analysis. Mass spectra revealed the presence of ubiquinones (UQs) in fractions of high polyphenol to protein ratio. The dominant mass peaks observed in these fractions were identified as UQ-3, UQ-5, and UQ-7. Since the quinone group of UQs is involved in redox reaction, we discuss the possibility that UQs may contribute to the antioxidant/proxidant activity of these complexes.
Highlights
Protein-polyphenol complexes are an integral part of honey colloids [1,2,3]
Honey high molecular complexes were precipitated using a mixture of methanol: ethanol: Honey highfollowed molecular complexes were precipitated using a by mixture of digestion methanol:of ethanol: isopropanol
We have previously reported that honey protein-polyphenol by size-exclusion chromatography into two groups differing complexes in molecular size, be protein to
Summary
Protein-polyphenol complexes are an integral part of honey colloids [1,2,3]. Through the interaction with other proteins and polyphenols, are able to form high molecular weight complexes and aggregates. The driving force in the protein-polyphenol complexation is a hydrophobic force/effect which is responsible for the formation of colloidal particle. Due to the hydrophobic effect, the hydrophilic proteins exposed to the outside of particle interact with aqueous sugar solution while burying nonpolar, hydrophobic molecules, such as polyphenols and other terpenoids with ring structures, inside the colloid [4,5]. Into transient or irreversible protein-polyphenol complexes depends on whether the interaction between these molecules leads to formation non-covalent or covalent bonds. The type of the bond, in turn, is determined by the polyphenol basic structure, the degree of hydroxylation, glycosylation on one hand and acylation, conjugation with other phenolics, and polymerization on the other hand, respectively [2,5,6,7]
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