Unique Pattern of Protein-Bound Maillard Reaction Products in Manuka (Leptospermum scoparium) Honey

Unique Pattern of Protein-Bound Maillard Reaction Products in Manuka (Leptospermum scoparium) Honey

Abstract: As a unique feature, honey from the New Zealand Manuka tree (Leptospermum scoparium) contains substantial amounts of dihydroxyacetone (DHA) and methylglyoxal (MGO). Though MGO is a reactive intermediate in the Maillard reaction, very little is known about reactions of MGO on honey proteins. We hypothesized that the abundance of MGO should result in a particular pattern of protein-bound Maillard reaction products (MRPs) in Manuka honey. A protein-rich high-molecular weight fraction was isolated from 12 Manuka and 8 non-Manuka honeys and hydrolyzed enzymatically. By HPLC-MS/MS, 8 MRPs, namely N-ε-fructosyllysine, N-ε-maltulosyllysine, carboxymethyllysine, carboxyethyllysine (CEL), pyrraline, formyline, maltosine, and methylglyoxal-derived hydroimidazolone 1 (MG-H1), were quantitated. Compared to non-Manuka honeys, the Manuka honeys were characterized by high concentrations of CEL and MG-H1, while the formation of N-ε-fructosyllysine was suppressed, indicating concurrence reactions of glucose and MGO at the ε-amino group of protein-bound lysine. Up to 31% of the lysine and 8% of the arginine residues, respectively, in the Manuka honey protein can be modified to CEL and MG-H1, respectively. CEL and MG-H1 concentrations correlated strongly with the MGO concentration of the honeys. Manuka honey possesses a special pattern of protein-bound MRPs, which might be used to prove the reliability of labelled MGO levels in honeys and possibly enable the detection of fraudulent MGO or DHA addition to honey.

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