CONTRIBUTION CHIMIQUE A LA DEFINITION DE LA QUALITE : EXEMPLES DES SPIRITUEUX DE MYRTE (MYRTUS COMMUNIS L.) ET DE CEDRAT (CITRUS MEDICA L.) DE CORSE
This thesis, developed in partnership with Mavela Company and INRA of Corsica, focuses on the study of two plants traditionally used in Corsica for spirit preparations (Liqueur and Eau-de-vie): common myrtle (Myrtus communis L.) and citron (Citrus medica L.). The thesis is divided into two main parts: * A fundamental part; the aim is to establish a methodology for the analysis of phenolic composition of alcoholic beverages by liquid chromatography coupled with mass spectrometry of the one hand, and to identify the flavonoid fragmentation rules, on the other hand. * An applied part; the objective is the quality definition of Corsican spirits using chemical markers. For this purpose, the intraspecicific chemical variability of M. communis berries and the characterisation of several citron varieties are studied in terms of volatile and phenolic compositions. The volatile composition of M. communis is dominated by α-pinene and 1,8-cineole whereas the phenolic composition is rich in myricetin, myricetin-3-O-arabinoside, myricetin-3-O-galactoside and epigallocatechin. These terpenic and phenolic "fingerprint" of M. communis berries are also reported in corresponding liqueurs and eau-de-vie. Furthermore, essential oil of myrtle berries is homogeneous in all sample locations. Morphological, genetic and chemical characteristics of 24 citron cultivars are used to differentiate "ancestral" varieties from "hybrid" varieties. Based on morphological and genetic diversity analysis, 13 cultivars included Corsican citron (Citrus medica L. var. corsican) are considered like ancestral citrons while the other 11 varieties are hybrids between citrons and other species of Citrus genus. Essential oils from ancestral citrons are distinguished from other varieties by limonene/neral/geranial or limonene/nerol/geraniol for leaf chemotypes and limonene/ץ-terpinene or limonene/neral/geranial for peel chemotypes. The distinction between ancestral and hybrid citrons could not be demonstrated using phenolic composition. The chemical analysis of liqueurs produced from Corsican citron is also investigated to study the influence of fruit maturity on spirit qualities. It appears that the harvest date has no impact on the volatile compositions. In contrast, the phenolic acid concentrations and their derivatives decreased sharply during fruit development. In addition, the quality assessment of alcoholic beverages depends on the experimental conditions of preparation. Finally, this thesis is the first step to establish by official designations a program for the protection of geographical and botanical origins of these Corsican productions.