A new look on protein-polyphenol complexation during honey storage: is this a random or organized event with the help of dirigent-like proteins?

PLoS One. 2013 Aug 30;8(8):e72897. doi: 10.1371/journal.pone.0072897. eCollection 2013.

Abstract

Honey storage initiates melanoidin formation that involves a cascade of seemingly unguided redox reactions between amino acids/proteins, reducing sugars and polyphenols. In the process, high molecular weight protein-polyphenol complexes are formed, but the mechanism involved remains unknown. The objective of this study was twofold: to determine quantitative and qualitative changes in proteins in honeys stored for prolonged times and in different temperatures and to relate these changes to the formation of protein-polyphenol complexes. Six -month storage decreased the protein content by 46.7% in all tested honeys (t-test, p<0.002) with the rapid reduction occurring during the first three month. The changes in protein levels coincided with alterations in molecular size and net charge of proteins on SDS -PAGE. Electro-blotted proteins reacted with a quinone-specific nitro blue tetrazolium (NBT) on nitrocellulose membranes indicating that quinones derived from oxidized polyphenols formed covalent bonds with proteins. Protein-polyphenol complexes isolated by size-exclusion chromatography differed in size and stoichiometry and fall into two categories: (a) high molecular weight complexes (230-180 kDa) enriched in proteins but possessing a limited reducing activity toward the NBT and (b) lower molecular size complexes (110-85 kDa) enriched in polyphenols but strongly reducing the dye. The variable stoichiometry suggest that the large, "protein-type" complexes were formed by protein cross-linking, while in the smaller, "polyphenol-type" complexes polyphenols were first polymerized prior to protein binding. Quinones preferentially bound a 31 kDa protein which, by the electrospray quadrupole time of flight mass spectrometry (ESI-Qtof-MS) analysis, showed homology to dirigent-like proteins known for assisting in radical coupling and polymerization of phenolic compounds. These findings provide a new look on protein-polyphenol interaction in honey where the reaction of quinones with proteins and polyphenols could possibly be under assumed guidance of dirigent proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Chromatography, Gel
  • Honey / analysis*
  • Molecular Sequence Data
  • Molecular Weight
  • Peptides / chemistry
  • Plant Proteins / chemistry
  • Plant Proteins / metabolism*
  • Polyphenols / metabolism*
  • Preservation, Biological*
  • Quinones / metabolism
  • Sequence Homology, Amino Acid
  • Spectrometry, Mass, Electrospray Ionization
  • Staining and Labeling
  • Temperature
  • Tetrazolium Salts / metabolism

Substances

  • Peptides
  • Plant Proteins
  • Polyphenols
  • Quinones
  • Tetrazolium Salts

Grants and funding

This work was supported in part by the grant from the Ontario Centres of Excellence (number BM 50849 to KB) and the OCE graduate student stipend award (LM). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.