# Construction of IsoVoc Database for the Authentication of Natural Flavours  
[PERSON]  
1 Department of Environmental Sciences, Jozef Stefan Institute, 1000 Ljubljana, Slovenia; [EMAIL_ADDRESS]  
as hydrogen and carbon (\({}^{2}\)H/\({}^{1}\)H, \({}^{13}\)C/\({}^{12}\)C), which is increasingly being applied in food quality control and in determining the authenticity of natural flavourings. Much effort has also gone into developing isotopic methods to detect adulteration of natural products with synthetic compounds. Among them, gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) seems to be the most specific and sophisticated method that can discriminate between natural and synthetic aromas based on the isotopic values of selected volatile organic compounds, VOCs [7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25]. The use of GC-C-IRMS is the subject of a review by [PERSON] et al. [8] and a paper by [PERSON] et al. [26] in which the authors emphasise the importance of the relevant analytical conditions to obtain precise isotopic ratios. Articles on determining the authenticity of fruit volatile organic compounds based on GC-C-IRMS are summarised in Appendix A (Table A1). These studies cover, for example, raspberry [10; 13; 18; 19; 27], peach [7; 11; 23; 25], strawberry [7; 8; 20], apple [16; 25; 28], nectarine [11; 23; 25], pineapple [7; 9], and orange [15; 25]. Many aromatic characteristics are shared between different fruits. However, each fruit is characterised by a distinctive aroma that depends on the VOCs present, concentration and perception threshold of individual volatile compounds [29]. Among these aromatic substances, special attention is paid to those compounds that create a fruit's characteristic aroma and are, therefore, likely to be falsified [29; 30]. Studies looking at more than five different VOCs are scarce [7; 12; 16; 20; 22], and within those, only two address more than one fruit type [7; 16]. In both studies, headspace solid-phase microextraction (HS-SPME) is used to extract the VOCs. The method offers many advantages such as simplicity, reduced time, improved repeatability, lower sample contamination probability [31], and finally, it does not cause isotopic fractionation [26]. HS-SPME-GC-C-IRMS has been used in all four fruit authenticity studies after 2010, proving its suitability as a tool for authenticity verification [7; 15; 16; 32]. Besides fruits, the method has been successfully applied for determining the authenticity of other aromas such as vanilla [31; 33; 34], citrus essential oils [15; 35], wine [36; 37; 38], and truffle oil [39]. When assessing authenticity, it is essential to have a comprehensive database of authentic samples [16; 40; 41; 42]. The guidelines on the structure and data collection of such a database are presented by [PERSON] et al. [41]. For example, verification of aroma authenticity is achieved by measuring the isotope values of investigated aroma compounds and comparing the obtained isotopic values with those of reference samples present in the database. Samples containing one or more compounds outside the range established for authentic aroma compounds will be suspected of being adulterated [18]. A limitation of such a database is that it represents only a snapshot in time and requires continuous updating, evaluation, and processing. In addition, using a single fruit type, which is the case in several studies, is insufficient for determining authenticity since different fruit types can have different isotopic ratios [7; 8; 11]. In addition, all properties that might influence isotopic values must be carefully studied and included in the database. For example, the aroma extraction process must be investigated for evidence of isotopic fractionation, i.e., enrichment of one isotope relative to another. So far, this phenomena has only been addressed by [PERSON] et al. [28] when investigating the technological processing of apple aroma. In this instance, the authors did not observe any isotopic fractionation.