## 2 Isolation Techniques for Volatiles in Honeys  
The specificity of honey products, _i.e._, flavor, aroma, color and texture, depends predominantly on the type of flowers, or plants, from where bees take the nectar, or the honeydew, to produce honey. Some other factors have a lesser influence on the properties of honey, _i.e._, the physiology of bees and their foraging habits, the climatic conditions (temperature, humidity) and the post-collection processing. Naturally, bees will forage any type of flower they can reach, and in consequence the honey produced mostly has a blend of flavors and is commonly sold in the market simply as honey or mixed-flower honey [18]. In this light, honey is a highly complex substrate to analyze, since it contains many volatile components with different chemical structures of low concentration in a sugar matrix where polar substances are the major components [19]. Due to its low concentration, it is necessary to remove the sugars which are the major components in honey before isolating the volatiles [20]. The extraction of these compounds prior to analysis by gas chromatography-mass spectrometry (GC-MS) has been carried out by numerous techniques, all of which have various advantages and disadvantages [21]. However, the composition of the honey volatiles show strong variability according to the extraction systems, since the volatility and polarity of each compound significantly affects the recovery percentage [22]. Some of these methods for instance, hydrodistillation (HD), liquid-liquid extraction (LLE), simultaneous steam distillation extraction (SDE) or Likens-Nickerson simultaneous distillation extraction (LNSDE) and micro-simultaneous steam distillation-solvent extraction (MSDE) utilize heat; however, heat treatment can lead to the formation of furan and pyran derivatives due to the effect of heat on sugar or amino acids (non-enzymatic browning reaction/Maillard reaction) [23]. Moreover, sensitive compounds are easily oxidized or decomposed and new components arise that do not belong to the aroma of honey [21]. Furthermore, the aforementioned methods and ultrasonic solvent extraction (USE) equally implement the use of solvents which is disadvantageous, even though the most commonly used low polarity solvents extract neither water nor sugar from honey [24]. USE aids extraction by significantly reducing extraction times and greatly improving extraction efficiency since the mechanical effect of the ultrasound would agitate the extraction solvent providing a greater penetration of the solvent into the matrix via cavitation [25]. The use of chemical solvents can solubilise non-volatile compounds and contaminate the GC port. Also, some analytes can be masked by the solvent and elude the GC column inhibiting detection as well as some can be lost during solvent removal [20,23]. Above all, the solvents are expensive and toxic, therefore, present safety and health issues [26]. The solvents usually employed include n-hexane, acetone, chloroform, dichloromethane, diethyl ether, aqueous methanol, pentane, mixture of pentane and diethyl ether (1:2 v/v) [25,27]. USE does not require heat and helps in the isolation of both low and high molecular weight compounds that are good potential markers for the determination of honey origin [21]. Solvent extraction methods have been used for VOC extraction, whether by means of direct extraction or SDE. [PERSON], [PERSON] _et al_. [25] in an attempt to develop an easier solvent extraction method, compared HD to USE for the isolation of volatile compounds from two unifloral honeys of _Robinia pseudoacacia_ and _Castanea sativa_ L. They revealed that USE gave the most representative profile of all honey volatiles (without artifacts) as well as it enabled the extraction of low molecular weight semi volatile markers especially benzoic, vanillic and phenyl acetic acids. [PERSON] _et al_. [19] equally compared three extraction techniques; SDE, LLE and solid phase extraction (SPE) that were employed in the extraction of volatiles from rosemary honey.