A chemical investigation of some New Zealand honeys

Abstract

Ether extracts were made from aqueous solutions of various floral types of New Zealand honeys with the use of a continuous liquid/liquid extractor. The components of the extracts were methylated before being separated and identified by gas chromatography and mass spectrometry. When a component could not be identified in this way, bulk extraction of representative unifloral honey samples was carried out and the extractives separated by preparative layer chromatography. The structures of the major components were then elucidated by techniques such as high resolution probe mass spectrometry and one and two dimensional ¹H and ¹³C nuclear magnetic resonance spectroscopy, and on one occasion also by X-ray crystallography. Classes of compounds identified include hydrocarbons, straight chain mono- and dibasic acids, aromatic substances, monoterpenes and degraded carotenoid-like extractives. Compounds reported for the first time in honey include 2,6-dimethyl-6(8)-hydroxy-2-trans-2, 7-octadienoic acid, 3 ,5 ,5-trimethylcyclohex-2-en-1-one, 3 ,5 ,5-trimethylcyclohex-2-ene-1,4- dione, 4-hydroxy-4-(3-oxo-1-butenyl)-3,5,5-trimethylcyclohex-2-en-1-one, 4- (3-oxo-1-butenylidene)-3 ,5 ,5-trimethylcyclohex-2-en-1-one, trans-cis and trans-trans-abscisic acid, 1,4-dihydroxybenzene and 2,6,6-trimethyl-1-(3- oxo-trans-1-butenyl)-cyclohexane-trans-cis-l,2,4-triol. The triol appears to be a new compound. Quantitative analyses of extractable organic substances from a series of white clover type, manuka, ling/heather, thyme, nodding thistle, vipers bugloss, kamahi and willow honeys afforded chromatograms which serve to uniquely characterise the floral sources of the honeys. Correlation was sought between the occurrence of extractable organic substances and the non-peroxide antibacterial activity of honey. Various potential antibacterial components were identified in this way. Quantitative testing of the pure compounds showed that 1,4-dihydroxybenzene probably accounts for all of the non-peroxide antibacterial activity of vipers bugloss honey, and that 4-hydroxy-3,5-dimethoxybenzoic acid and 2-hydroxy-3-phenylpropionic acid account for 0.2-0.35% and 1.6-3.2% respectively of the non-peroxide antibacterial activity in manuka honey.