Fast quality screening of vegetable oils by HPLC-thermal lens spectrometric detection

Isocratic reversed-phase HPLC with thermal lens spectrometric (TLS) detection enabled identification of linseed, olive, sesame, and wheat germ vegetable oils to control the authenticity of the oils based on characteristic carotenoid/carotene profiles. Four characteristic regions of carotenoids (i.e., lutein, xanthophyll, carotene, and lycopene) have been identified in each type of oil. The concentrations of total β-carotene (BC) and α-carotene (AC), together with trans- to cis-isomers of β-carotene (TBC/CBC) and BC/AC ratios were shown to be reliable and useful indices for fast screening of oils for nutritional quality. The oil TBC/CBC ratio and the BC concentration (in μg/mL) should meet the following numerical criteria: linseed (≥2:1, ≥1.7), olive (≥3:1, ≥0.4), sesame (≥1:1, ≥0.1), and wheat germ oil (≥1:1, ≥1.7). Based on the above criteria, unsatisfactory olive oils differed significantly from the consumable ones. Likewise, the concentration of AC in consumable wheat germ and sesame oil should not be lower than 0.6 and 0.02 μg/mL, respectively. The AC level in saf-flower oil should not be higher than 0.04 μg/mL. The BC/AC ratios exceeding 3:1, 6:1, and 8:1 should be used as an additional quality requirement for consumable wheat germ, sesame, and saf-flower oil, respectively.