Pilot study on the discrimination of commercial Leptospermum honeys from New Zealand and Australia by HPLC–MS/MS analysis

Abstract

Manuka honey from New Zealand is derived from the nectar of Leptospermum scoparium and contains high amounts of methylglyoxal (MGO), which is responsible for its extraordinary antibacterial properties and its high market value. It was shown recently, that honeys from Australian Leptospermum species, often referred to as “jellybush honey”, also contain MGO. Recently, an official method has been published by the Ministry of Primary Industries (MPI) New Zealand to characterize monofloral and multifloral manuka honey from New Zealand, based on the concentration of the phytochemical compounds 2′-methoxyacetophenone (2-MAP), 2-methoxybenzoic acid (2-MB), 3-phenyllactic acid (3-PLA) and 4-hydroxyphenyllactic acid (4-HPLA). Here we show that these phytochemical markers are suitable to differentiate honeys originating from Leptospermum species from New Zealand or Australia, respectively. Three non-manuka honeys and eight manuka honeys from New Zealand as well as four non-Leptospermum honeys and 15 Leptospermum honeys from Australia were analysed for their MGO content via RP-HPLC-UV and their 2-MAP, 2-MB, 4-HPLA and 3-PLA concentration via RP-HPLC–MS/MS. All non-manuka honeys contained only negligible amounts of MGO, whereas honeys from Leptospermum species contained up to 1100 mg/kg, independent of the geographical origin. No significant amounts of 3-PLA, 4-HPLA, 2-MB and 2-MAP were found in the non-manuka honeys. In contrast, all marker compounds were abundantly present in manuka honeys from New Zealand, thus enabling a characterization of monofloral or multifloral quality. All honey samples from Australian Leptospermum species contained 2-MAP in concentrations below the limit of detection. The concentrations of the other marker compounds ranged from 58 to 357 mg/kg for 3-PLA, from 1 to 3 mg/kg for 4-HPLA and from 26 to 175 mg/kg for 2-MB and were significantly different when compared to New Zealand manuka honeys. Based on the results of this study, the marker compounds suggested by the MPI might be useful to distinguish honeys derived from Leptospermum species of different geographical origins.