Identification of botanical biomarkers found in Corsican honey
Introduction
EU legislation (Council Directive 2001/110/EC) requires that the geographical origin of honey be presented on the packaging. Compliance with this legislation may be checked by measuring origin-specific parameters such as isotopic ratios and elemental composition (Kelly, Heaton, & Hoogewerff, 2005).
Monofloral honey is produced from nectar that is either wholly or mainly from a single species of plant. These honey types, from defined botanical sources, possess distinctive organoleptic characteristics (Bianchi, Careri, & Musci, 2005), are often traded at a higher price than honeys from mixed botanical sources and can thus be considered as premium products. Where additional properties are imparted by the exclusivity of the honey source, such as the antimicrobial properties of Manuka honey, the price of the product is further increased (Weston, Brocklebank, & Lu, 2000). To protect the consumer from fraudulent mislabelling of inferior honey, methods are required for the verification of labelling claims that result in elevated market price. Previous studies have focussed on either the identification of biomarkers of botanical origin or using a combination of chemometrics and spectroscopic profiling techniques to develop statistical models that describe a specific monofloral honey (Karoui, Dufour, Bosset, & De Baerdemaeker, 2007). Studies performed using spectroscopic profiling techniques (so called fingerprinting methods) often provide little information about the nature of the compositional changes that result in successful distinction between honey types. NMR spectroscopy, however, provides detailed information relating to specific components of complex mixtures of compounds. Therefore, 1H NMR spectroscopy is a particularly powerful analytical technique for the characterisation of biomarkers. Several properties of the technique such as reproducibility and limited sample preparation times ensure that it is suited to this role. The unbiased nature of the technique is such that any soluble molecule (<30 kDa) that contains non-exchangeable 1H atoms will give an NMR response. The inherent structural elucidation power of 1H NMR spectroscopy also enables the characterisation of novel or uncharacterised biomarkers. The work presented in this manuscript applied genetic programming (GP) (Davis, Charlton, Oehlschlager, & Wilson, 2006) to 1H NMR spectroscopic data to successfully determine the 1H chemical shifts of biomarker resonances. We have previously demonstrated the application of 1H NMR spectroscopy to determine the presence of biomarkers using principal components analysis (PCA) of instant coffee (Charlton, Farrington, & Brereton, 2002).
Several biomarkers relating to the botanical source of the pollen present in honey have been identified. For example, 2,5-dihydroxyphenylacetic acid (Cabras et al., 1999) and a range of norisoprenoids (Weston et al., 2000) have been identified as being specific components of strawberry-tree honey. Similarly, eucalyptus honey can be characterised by the presence of 2-hydroxy-5-methyl-3-hexanone and 3-hydroxy-5-methyl-2-hexanone (de la Fuente, Valencia-Barrera, Martinez-Castro, & Sanz, 2007) whilst ellagic acid is a biomarker of heather honey (Andrade, Ferreres, Gil, & Tomas-Barberan, 1997).
The importance of understanding the composition of honey from a human health point of view is also valuable. There have been many reported beneficial effects from the use or consumption of honey including improved oral health (Molan, 2001), antimicrobial properties (Ceyhan & Ugur, 2001) and wound healing effects (Mphande, Killowe, Phalira, Jones, & Harrison, 2007). Conversely, the ingestion of grayanotoxins in ‘mad honey’ (Koca & Koca, 2007) can lead to mortality.
A previous study utilised NMR spectroscopy for the characterisation of Corsican honey (Donarski, Jones, & Charlton, 2008). Multivariate statistical methods were used to identify spectral regions that are characteristic of the geographical origin of Corsican honey. A wide range of European honeys were used to establish the validity of the multivariate models. The approach taken resulted in the identification of a small number of peaks in the NMR spectrum, the intensities of which were used to identify Corsican honey with an overall accuracy of 96.2%. The compounds giving rise to these peaks were only partially characterised and their source was unknown. In this manuscript we investigate the peaks identified in the NMR spectrum that are characteristic of Corsican honey and correlate these with specific honey types. Data generated from the NMR spectroscopic analysis of a second harvest of Corsican honey is included here for the first time and demonstrates the validity of the biomarkers identified.
Section snippets
Materials
Honey collected during Year 1: Honey (182 samples) was collected from five countries: Austria (18), France (129), Germany (18), Ireland (2) and Italy (15).
Honey collected during Year 2: Honey (192 samples) was collected from four countries: Austria (23), France (136), Germany (18) and Italy (15).
Commercial chestnut honey: Two chestnut honeys were purchased from commercial outlets. The honeys were from the French region of Périgord and the Italian region of Piemonte.
All non-commercial honeys
Results and discussion
It was previously reported that biomarkers of geographical origin were detected in Corsican honey analysed by 1H NMR spectroscopy (Donarski et al., 2008). The results were obtained from the statistical analysis of honey samples collected during Year 1 and demonstrated the utility of GP in the determination of biomarkers within complex NMR spectroscopic data. Results obtained from the statistical analysis of honey samples collected over both years are presented herein.
Conclusion
1H NMR spectroscopy has been shown to be a powerful analytical technique to screen for the presence of biomarkers of botanical origin in honey. The chemical properties inherent in pharmacoactive (either toxic or beneficial) organic compounds is such that when analysed by 1H NMR spectroscopy they will resonate at chemical shifts usually not observed naturally in food matrices and are therefore often resolved. This is demonstrated well by the unique chemical shifts of kynurenic acid observed in
Acknowledgments
The authors thank the EU TRACE project and the UK Food Standards Agency for funding this work.
The honeys utilised in this research were collected as part of the TRACE (www.trace.eu.org) project by the Czech Bee Research Institute (Year 1) and Olivier Bidet (Year 2). The honeys were sub-sampled and distributed by The Irish Agriculture and Food Development Authority (Year 1) and the Institute of Chemical Technology, Prague (Year 2).
The information contained in this article reflects the authors’
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2018, Saudi Journal of Biological SciencesCitation Excerpt :Monofloral honey is produced from nectar that mainly originates from a single plant species and possesses distinctive organoleptic characteristics. These honey types of distinct botanical origin are often traded at a higher price than honeys from mixed botanical origins and can thus be considered premium products (Donarski et al., 2010; Can et al., 2015). In Saudi Arabia, honey is a highly regarded product.