Dynamic Olfactometry: evaluation of odour intensity and stability of Citronella Oil loaded Solid Lipid Nanoparticles

The Dynamic Olfactometry is a satisfactory method to determine objectively the odour concentration of volatile samples, using a human selected panel. The essential oils (EOs) are composed by lipophilic and highly volatile secondary plant metabolites, including terpenoids, phenol-derived aromatic and aliphatic components. The terpenoids are volatile organic compounds (VOCs) that undergo to oxidative and isomerizzation processes due to the air, light, moisture and high temperatures. Moreover, as a consequence of the high vapour tension of VOCs, the efficacy of EOs are very limited in the time. The Citronella Oil (C.O.) is used extensively as a source of perfumery chemicals or repellent substances, as citronellolal, citronellol and geraniol, that are responsible to their instability. The nanoencapsulation in drug delivery systems represents an efficient strategy to improve the stability and efficacy of EOs-based formulations. In this work the C.O. is formulated in solid lipid nanoparticles (SLNs), by ultrasonication method. The mean diameter (MD), polidispersity index (PDI) and zeta potential (PZ) of C.O. loaded SLN are determined immediately and after one month from production, showing a good long term stability. The aim of the work is the evaluation of odour concentration of C.O. free and loaded in SLN, in order to understand how the formulation can influence volatility, stability and release in SLN formulation. The Dynamic Olfactometry is performed, according to the regulation UNI EN 13725:2004. The results are expressed in OUE/m3 (European Odour Unit, OUE for m3), that represents the amount of odorant, evaporated in 1 m3 of neutral gas, inducing a physiological response, equal to a reference gas used, n-butanol, on a panel. The figure 1 and 2 showed the relationship between the odour intensity (OUE/m3) of the free oil and loaded in SLN, at 2.5% and 0.25%, respectively. The odour intensity is followed for 96 hours. After 24 hours, the odour intensity of free oil is not perceptible at both concentrations used. On the contrary, the odour intensity of C.O. loaded in SLN at 96 hours is 580 OUE/m3, at 2.5%, and 250 OUE/m3, at 0.25%. The obtained results for C.O. loaded in SLN at 2.5% and 0.25%, confirmed a prolonged and concentration-dependent effect of C.O. formulations.