Characterisation of Malaysian honeys and electrochemical detection of gallotannin for pure honey identification

Abstract

Seventeen samples (n = 17) of Malaysian gelam, acacia, nanas, tualang and kelulut honeys were analysed for their physicochemical, biochemical and phytochemical properties to evaluate their influence on floral source and bee type. Comparisons were also made with synthetic honeys to determine a suitable measure for fast identification of pure honey from synthetic honey. Solid phase extraction (SPE) was utilised for isolation of phenolic compounds in honey samples. The phenolic compounds present in the samples were analysed using high performance liquid chromatography-diode array detector (HPLC-DAD) and liquid chromatography tandem mass spectrometry (LC-MS/MS). Three electrode systems were utilised for rapid identification of pure Malaysian honeys. Properties of honey were shown to be influenced by the floral source and bee type to the lesser extent. Kelulut honeys were observed of having lower pH, higher free acid, moisture and ash contents as well as higher electrical conductivity (EC), the properties that distinguish Trigona honey from the common Apis honey. Antioxidant properties were different for the five types of honey with Trigona honey dominating most of the antioxidant tests. Up to 16 phenolic compounds were identified using HPLC-DAD system. Similar dominant compounds were observed between tualang and acacia honeys, and between kelulut and gelam honeys, suggesting that the floral source of unifloral honey is an equally important food source for the analysed multifloral honey. More phenolic compounds were detected spectrometrically using full scan method and multiple reaction monitoring (MRM). Plant gallotannin, penta-O-galloyl-β-D-glucose (PGG) was successfully detected at low potential 0.173 V vs Ag/AgCl in pH 7 phosphate buffer solution using glassy carbon electrode (GCE) without any prior electrode activation, chemical modification and pre-concentration at the GCE. The PGG detection in blank pure honey and via standard addition approach in the Malaysian honeys revealed its presence only in the pure honeys. The present study suggested that electrochemical detection of PGG using GCE could be used as a tool for pure honey identification through a rapid and simple method rather than other conventional, highly-technical, expensive and time-consuming analytical techniques.