Raman Spectroscopic Investigation of Carotenoids in Oils from Amazonian Products

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In this work several different natural products from the Amazon forest were analyzed by means of Raman spectroscopy, using the 1064-nm laser line as a way to obtain the spectra. All the oil samples from handmade produced buriti, babaçu, and pequi, as well as the refined andiroba, cold-pressed passion flower, and palm oils, were acquired in the local market in Brazil. Some products present in all the spectra of the ν(C˭C) vibration, observed in the 1525 cm−1 region, the ν(C-C) mode near 1158 cm−1, and the ρ(C-CH3) mode near 1008 cm−1, can be seen; all these bands are assigned generally to the presence of a C9 carotenoid and can be more precisely attributed to the ν1, ν2, and δ modes of β-carotene. Also, the characteristic Raman scattering bands common to all the oils arising from vibrations of the hydrocarbon chains can be observed, namely, aromatic ring C˭C stretching at 1658 cm−1 (ν(C˭C)); CH2 scissoring deformation at 1439 cm−1 (δ(CH2); vibrations of in-phase methylene twisting at 1301 cm−1, and symmetric CH rocking in unconjugated cis-double bonds at 1270 cm−1 (δ(C–H)), as well as C˭O stretching from the ester groups at 1747 cm−1 [ν(C˭O)]. It is noteworthy that most natural oils have a major contribution of components of some of the main fatty acids: palmitic (C16), oleic (C18:1), and linoleic (C18:2), and no carotenoid was detected in the Raman spectra of the white babaçu oil or in the pale yellow andiroba oil. As a major conclusion, direct Raman spectroscopic measurements using a near-infrared wavelength as the excitation source can be used as a primary test to monitor the quality control of natural oils extracted from the Amazon forest, namely, andiroba, burity, babaçu, and pequi oils.