Évaluation des activités biologiques des huiles essentielles du citron (Citrus limon)
Himed Merniz, Louiza
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The main objective of this work is to test the encapsulated essential oils in order to solve the problem of their instability, and apply them in light margarine in order to follow its oxidative stability and to evaluate its acceptability. The essential oils were extracted by hydrodistillation and cold pressing from two varieties of Citrus limon: Eureka and Lisbon. Recovered oils were analyzed by GC/MS to identify their constituents. As main results obtained, the extraction yield was greater by hydrodistillation than by cold pressure. The composition of the oils extracted was different but it was characterized by a dominance of monoterpenes, followed by oxygenated monoterpenes and then sesquiterpenes and finally oxygenated sesquiterpenes. High levels of limonene were recorded (61% - 67%). The antioxidant activity of the extracted oils was evaluated by several tests, namely the test for the inhibition of lipid peroxidation (β-carotene bleaching and the β-carotene qualitative test), the free radical scavenging test (DPPH and ABTS+), the test of the reducing power (CUPRAC and FRAP) and finally the test of the chelating power. The results obtained showed an interesting antioxidant power of Eureka oils extracted by cold pressure compared to other oils. On the other hand, the chelating power was less important for all oils compared with EDTA. The antimicrobial power of the oils was evaluated by two tests to determine the susceptibility of the strains and the microbiological parameters CMI, CMB and CMF. The strains tested are of 15, including 9 bacterial strains (2 Gram positive and 7 Gram negative) and 6 fungal strains. The results showed that all strains are sensitive and the oils have interesting antimicrobial properties. The essential oils of the Eureka variety extracted by cold pressing, having the best antioxidant power, were encapsulated in amorphous silica and then characterized by SEM, ATR and TGA and an evaluation of ther antioxidant power. The results showed a significant encapsulation efficiency of 95.87%. No interaction between oils and SiO2 has been reported. On the other hand, a thermogravimetric resistant of the encapsulated oils was noticed compared to the free oils. The antioxidant activity of essential oils was not changed after encapsulation. Three formulas of light margarine were developed: control margarine (CM), free essential oil margarine (FOM) and encapsulated oils margarine (EOM). A physico-chemical characterization, a determination of the resistance to forced oxidation and sensory analysis were carried out. The results showed that the physico-chemical characteristics of margarines with essential oils are in accordance with the standards and the pre-established recipe and are not different from those of the control. The EOM showed resistance to forced oxidation comparable to that of the control (CM), however the resistance of the FOM is not interesting. The tasters of the three formulas showed a preference of the FOM, then of the EOM and finally of the CM. Therefore it would be interesting to proceed with the industrial formulation of a lemon essential oil margarine.