Volatile Compounds of Viola odorata Absolutes: Identification of Odorant Active Markers to Distinguish Plants Originating from France and Egypt

Abstract

Absolutes isolated from Viola odorata leaves, valuable materials for the flavor and fragrance industry, were studied. Violets are mainly cultivated in France and Egypt and extracted locally. The absolutes of the two origins showed different olfactory profiles both in top and heart notes, as evidenced by sensory analysis. The aims of this study were i) to characterize the volatile compounds, ii) to determine the odorant-active ones, and iii) to identify some markers of the plant origin. Two complementary analytical methods were used for these purposes, i.e., headspace solid-phase microextraction (HS-SPME) using different fiber coatings followed by GC/MS analysis and gas chromatography - olfactometry/mass spectrometry (GC-O/MS) applied to violet leaf extracts. From a total of 70 identified compounds, 61 have never been reported so far for this species, 17 compounds were characterized by both techniques (with seven among them known from the literature), 23 compounds were solely identified by HS-SPME GC/MS (among them only two being already mentioned as components of violet absolutes in the literature), and, finally, 30 compounds were only identified by GC-O/MS. According to the HS-SPME GC/MS analyses, ethyl hexanoate and (2E,6Z)-nona-2,6-dienol were specific volatile compounds of the sample with French origin, while (E,E)-hepta-2,4-dienal, hexanoic acid, limonene, tridecane, and eugenol were specific of the samples with Egyptian origin. Additional compounds that were not detected by HS-SPME GC/MS analysis were revealed by GC-O analyses, some of them being markers of origin. Pent-1-en-3-ol, 3-methylbut-2-enal, 2-methoxy-3-(1-methylethyl)pyrazine, 4-ethylbenzaldehyde, β-phenethyl formate, and 2-methoxy-3-(2-methylpropyl)pyrazine revealed to be odorant markers of the French sample, whereas cis-rose oxide, trans-rose oxide, and 3,5,5-trimethylcyclohex-2-enone were odorant markers of the Egyptian samples.

Metabolomics for the Authentication of Natural Extracts Used in Flavors and Fragrances: the Case Study of Violet Leaf Absolutes from Viola odorata

“…Indeed, according to our previous study on violet leaves absolute, this extract has more floral and green notes than that of Egyptian origin, which is qualified as earthy because it reminds the odor of soil or ground. Besides, concentration in ( E , Z ) ‐ 2,6‐nonadienal has been found twice higher (1.5 mg/g of absolute) in samples of French origin than those of Egyptian origin (0.6 mg/g of absolute) . We applied our metabolomic approach to discriminate these adulterations in Egyptian absolutes.…”

“…Anyway, we cannot conclude on the whole extract. The impact of these both variation sources on the volatile fraction can be important and can highly change the olfactive quality of the extract .…”

“…( E , Z )‐2,6‐nonadienal, also known as ‘cucumber aldehyde’, is one of the most powerful odorant component of V. odorata l . extracts . Therefore, adulteration with pure ( E , Z ) ‐ 2,6‐nonadienal could artificially enhance the quality of the product.…”

“…leaf extract, the plant being historically cultivated in France for the perfume industry. The main olfactive features of this absolute are associated to the green cucumber‐like and flowered notes . Violet flower is not extracted for the flavors and fragrances industry, as the yields are very low.…”

“…Moreover, addition of methyl linoleate (ML), a nonvolatile synthetic compound, was another example chosen for its low price and natural occurrence in violet leaves extract. Lastly, synthetic ( E , Z )‐2,6‐nonadienal was selected for its high odorant activity responsible of the cucumber smell and for its trace level in violet leaves extract.…”