Fingerprinting pattern of orange essential oils in surfactant-free microemulsion by 3D fluorescence spectroscopy

The effect caused by surfactant-free microemulsion (SFME) systems in orange essential oil analysis was evaluated by 3D fluorescence spectroscopy. The SFME formation region was studied at different water:EO proportions (1:4, 1:2, 1:1, 2:1, 4:1 w/w) in the presence of propanol and octanol (10:3 w/w). Conductometric titrations indicated micellar aggregates containing EO (oil-in-water microemulsion) for the 4:1 proportion (droplets of hydrodynamic radius of 95.7 ± 5.3 nm). In such conditions, fluorescence increased allowing the use of 3D fluorescence spectroscopy to obtain spectroscopic fingerprint pattern that was used aiming discriminant analysis, considering nine EO Brazilian brands, along with unfold principal component analysis (UPCA). Cumulative variance of 96.7% was obtained for the first three principal components and score plots showed distinct location for each group. Preliminary study showed the capability of these systems in evaluating storage conditions, and adulteration. The impact of storage conditions was made over 21 days exposed to light with results showing large spectral differences compared to a sample stored in amber flask at 22°C. Adulteration of EOs by canola and mineral oil fortification was detected at different levels (1, 5, 10 and 20%, in mass proportion) and, in addition to the spectral differences, a change in microemulsion stability was observed.