Oct. 30, 2012

Honey Aroma Profiles for the Characterisation of Unifloral Honeys

  • Fig. 1: HS-SPME-GC/MS, TIC, aroma profiles of various single-type honeysFig. 1: HS-SPME-GC/MS, TIC, aroma profiles of various single-type honeys
  • Fig. 1: HS-SPME-GC/MS, TIC, aroma profiles of various single-type honeys
  • Fig. 2: HS-SPME-GC/MS, TIC, aroma profiles of Spanish orange honey
  • Fig. 3: HS-SPME-GC/MS, TIC, aroma profiles of lavender honey from France (A) and Spaon (B,C)
  • Fig. 4: HS-SPME-GC/MS, TIC, aroma profiles of Spanish rosemary honey
  • Fig. 5: HS-SPME-GC/MS, TIC, aroma profiles of acacia honey from Hungary (A), Rumania (B) and Coratia (C)
  • Table 1: Coloring and principle pollen forms of several single-type honeys [QSI, Bremen, 2011]
  • © Marianne Mayer

Unifloral honeys which can be primarily assigned to a single source of pollen have considerably higher prices than mixed honeys. In addition to the analysis of individual substances, recording of aroma profiles is a promising method for investigating the purity of these honeys.

Honey has always been an important and popular sweetener. Neither sucrose from sugar beet nor cane sugar have been able to replace honey due to its aroma and taste. This is also reflected in the figures for honey consumption. With a per-capita consumption of approximately 1.0 kg honey per year, Germany is one of the world leaders [1]. Above all, unifloral honeys with their typical taste and aroma which depend on the forage plant are becoming increasingly important, even though their retail price is considerably higher than that of mixed honeys. Investigation of the purity of these honeys is therefore especially important in the context of consumer protection and quality control. Up to now, microscopic analysis of the pollen (melissopalynology) has been the most important method for this. However, pollen from the same family of plants, e.g. the labiates rosemary and lavender (table 1) are very similar, which causes difficulties for the differentiation of the types of honey. Often, the proportion of pollen differs greatly according to its botanical origin and because of this the legally demanded minimum quantity depends on the main forage source. For example a sweet chestnut honey must contain at least 90 % Castanea sativa pollen; however a rosemary or lavender honey only contains 20 % rosmarinus or lavendula pollen. Because of this, experiments with alternative methods for the authentication of unifloral honeys, primarily chemical analysis methods have been carried out for many years. Here, analysis of secondary plant substances such as phenolic acids and flavonoids [3, 4] as well as the examination of aroma substances, which also originate from the secondary metabolism of the plants and are therefore specific to the source, has proved promising.

The aim of this study was therefore to record the aroma profiles of various types of honey in order to obtain characteristic differences for the forage sources.

Materials and Methods
Headspace Solid Phase Micro Extraction (HS-SPME-GC/MS) was used to record the aroma profiles.

The SPME fiber (DVB/CAR/PDMS, Supelco) was exposed in the vapor space above the diluted honey solution. At the same time, the headspace vial was situated in a thermostatically controlled agitator.

HS-SPME is an equilibrium reaction in which for simplicity it is assumed that three phases, namely the liquid phase of the sample, the gaseous region above the sample and the fiber coating compete for the substance under analysis [7]. The equilibrium is essentially influenced by the extraction conditions, which must therefore be optimized, as must the desorption conditions which affect the sensitivity of the method [8]. Gas chromatography separation is performed on a polar column with subsequent EI-MS detection in scanning mode. The conditioning of the SPME fiber, extraction and desorption were completely automatic due the aid of a Combi PAL system, so that extraction and gas chromatography could be combined in order to save time. The reproducibility of the method (in relation to the total peak area) was 2.9 % and the repeatability was 4.6 %.

With the optimized method 300 authentic honey samples from various types of honey were analyzed.

Initially the aroma profiles of honeys of a single type were compared with each other and then compared with the aroma profiles of other types of honey in order to obtain the specific differences between the forage plants.

The advantages of the HS-SPME-GC/MS method are illustrated with the example of the visually similar honey types orange, lavender, rosemary and acacia (table 1). In figure 1, the differences in the aroma compositions of the various types are already apparent. Even though differentiation of these types by color (and in the case of rosemary and lavender honey by pollen analysis) is difficult and these types also have similar pH values and conductivities [9], there are significant differences in the aroma profiles.

In addition, the congruence of the aroma profiles within a unifloral honey, even from different geographical locations, is clearly evident (fig. 2-5). The only differences are with regard to the peak intensities.

Because of this it was possible to produce characteristic GC profiles for the relevant types of honey and also to identify many prominent combinations, which can be used for authentication.

However, for the final declaration of type-specific aroma components, unifloral honeys obtained over several years must be analyzed in order to take natural fluctuations into account.

By means of HS-SPME-GC/MS it is possible to determine the botanical origin of unifloral honeys without tedious clean-up, so that this method can be used as a screening method for the verification of honeys.

We wish to thank Dr. Lüllman (Quality Services International, Bremen) for the provision of honey samples which have been securely identified by means of pollen analysis.

[1] www.honig-verband.de, Stand 19.10.2011
[2] Honigverordnung [Honey Ordinance], version dated: 16.01.2004. Honigverordnung dated 16. January 2004 (BGBl. I S. 92), last amendment by Article 9 of the Ordinance dated 8. August 2007 (BGBl. I S. 1816)
[3] Speer K. & Montag A.: DLR 80 (4), 103-105 (1984)
[4] Trautvetter S. et al.: Apidologie 40, 140-150 (2009)
[5] Soria A. e al.: Eur. Food Research Technol 228, 579-590 (2009)
[6] De la Fuente E. et al.: Food Chemistry 103, 1176-1180 (2007)
[7] Pawliszyn J.: SPME-Theory and Practice, Wiley-VCH (1997)
[8] Scheppers Wercinski S.A.: Solid Phase Microextraction: A Practical Guide, Marcel Dekker Inc. (1999)
[9] Leitsätze des Deutschen Lebensmittelbuches [Guidelines of the German Foodstuffs Code]: New version or amendment dated 30 May 2011




TU Technische Universität Dresden - Inst. für Lebensmittelchemie
Bergstraße 66
01062 Dresden

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