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

Abstract

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 safflower 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 safflower oil, respectively.Profiling of carotenoids in vegetable oils is of great nutritional and epidemiological interest. The separation, identification, and quantitation of trans/cis-isomers of β-carotene (TBC, CBC) in edible oils is important to measure antioxidant activity and for quality control. The cis-isomer(s) are either naturally present or formed during the processing of oils. In fruits and vegetables all-trans-β-carotene has been shown to undergo cis-isomerization (1), with the 9-cis-and 13-cis-stereoisomers being the predominant isomerization products.Various studies on the distribution of pigments in olives and olive oils have shown that the characteristics of olive oil depend on genetic, agronomic, environmental, and processing factors (2-7). The content of pigments differs greatly among single-variety virgin olive oils. Arbequina variety olives have chlorophyllides, esterified xanthophylls, α-carotene (AC), ξ-carotene, and phytofluene that are exclusive to this variety (2).The carotenoid (17-19%) and total chlorophyll (81-83%) fractions dominate in fresh olives, whereas lutein (10-11%) and β-carotene (4-5%) are the most abundant among the carotenoids (3). In virgin olive oils the concentration of total xanthophylls (including neoxanthin, mutatoxanthin, antheraxanthin, luteoxanthin, and violaxanthin) varies between 0.3 and 1.6 µg/g, whereas those of pheophytins, lutein, and β-carotene range from 3.3 to 51.4, 0.2 to 9.3, and 0.3 to 7.7 µg/g, respectively (3-7). However, the chlorophyll and carotenoid contents gradually decrease during olive fruit ripening (2). Separation, identification, and quantification of carotenoids and chlorophylls in olive fruit and in olive oils based on normal-phase HPLC (5,6), reversed-phase ion-pair HPLC (2,4), and TLC (3) hav...

Cyclic Voltammetry of Retinol in Surfactant Media and Its Application for the Analysis of Real Samples

“…It is caused by b-carotene absence in this oil that confirms by chromatographic analysis [35]. The found amount of retinol the linseed oil is probably explained by destruction of b-carotene from linseeds [36] during oil preparation process. As known, linseeds are characterized by one of the highest b-carotene content (about 15 mg/100 g) [34] in comparison with other oil seeds.…”

Differentiation of Refined and Virgin Edible Oils by Means of the trans- and cis-Phytol Isomer Distribution

“…The perfect marker should be present in all plant oils, and it should be changed during the technical refining process. One step forward was provided by Luterotti et al, who determined the distribution of trans / cis isomers of β-carotene by means of thermal lens spectrometry . Unfortunately, this analytical tool is not widely distributed in food control.…”

Separation and Direct Detection of Long Chain Fatty Acids and their Methylesters by the Non‐Aqueous Reversed Phase HPLC and Silver Ion Chromatography, Combined with CO Laser Pumped Thermal Lens Spectrometry

“…However, at present, such universality comes at a price of less favourable limits of detection. The relatively high IR background absorption of the mobile phases used in our experiments precludes, at least for the time being, NARP-HPLC-TLS and Ag-HPLC-TLS detectors from achieving spectacular sensitivities already obtained with the same technique in the visible region when quantifying trans-beta-carotene in human blood serum [29] and fish oil based supplementary drugs, [30] detecting carotenoids in the edible oils [31] and determining the content of lycopene in tomato purees. [32] A more judicious selection of the mobile phase could compensate for this effect; however, the choice of weakly absorbing and polar eluents that are also capable of achieving good chromatographic separation may be limited.…”