Simultaneous determination of sterols in edible oils by use of a continuous separation module coupled to a gas chromatograph

Detection of Chemlali extra-virgin olive oil adulteration mixed with soybean oil, corn oil, and sunflower oil by using GC and HPLC

Fatty acid composition as an indicator of purity suggests that linolenic acid content could be used as a parameter for the detection of extra/virgin olive oil fraud with 5% of soybean oil. The adulteration could also be detected by the increase of the trans-fatty acid contents with 3% of soybean oil, 2% of corn oil, and 4% of sunflower oil. The use of the ΔECN42 proved to be effective in Chemlali extra-virgin olive oil adulteration even at low levels: 1% of sunflower oil, 3% of soybean oil, and 3% of corn oil. The sterol profile is almost decisive in clarifying the adulteration of olive oils with other cheaper ones: 1% of sunflower oil could be detected by the increase of Δ7-stigmastenol and 4% of corn oil by the increase of campesterol. Linear discriminant analysis could represent a powerful tool for faster and cheaper evaluation of extra-virgin olive oil adulteration.

N-alkylpyridinium quaternization for assisting electrospray ionization of sterols in oil by quadrupole-time of flight mass spectrometry

RATIONALE

The illegal cooking oil has become a serious social problem and raised widespread alarm recently. However, an efficient and sensitive technique for identifying the potential illegal cooking oil is still unavailable, especially when mixed with the ordinary ones; there is an urgent need to develop an efficient method for identifying the illegal cooking oil. Sterols in the cooking oil could be used as an indicator to identify the source and quality of oil by detecting the kinds of phytosterols and zoosterols. However, those sterols are difficult to be ionized by electrospray ionization, which resulted in the low sensitivity in electrospray ionization (ESI)-mass spectrometric (MS) analysis.

METHODS

N-alkylpyridinium isotope quaternization was extended to charge label sterols in different cooking oil and attached N-cationic pyridinium tag onto the sterols in the presence of trifluoromethanesulfonic anhydride (Tf2 O); the kinds of sterols were identified and quantified by comparing d0 /d5 pairs and product scan from ESI-quadrupole-time of flight (Q-TOF) MS analysis.

RESULTS

The derivatized sterols were attached with permanent charge, resulting in the significant enhancement of ionization in ESI-Q-TOF MS analysis. The detection limits of analytes were improved to 0.02-0.05 ng/mL; different kinds of phytosterol, zoosterol and oxides were identified and quantified by comparing d0 /d5 pairs from full scan and product scan. The method was applied in the detection of zoosterol for identifying the potential recycled cooking oil, even when the illegal oil has been blended into the ordinary one. More zoosterol was detected in the recycled oil compared with other cooking oil.

CONCLUSIONS

The use of N-alkylpyridinium isotope quaternization method provided an alternative method for identifying the potential illegal cooking oil.

Classification of vegetable oils according to their botanical origin using sterol profiles established by direct infusion mass spectrometry

A simple and quick method to classify vegetable oils according to their botanical origin, based on direct infusion of sterol extracts into a mass spectrometer, was developed. Using mass spectrometry (MS) with either an electrospray ionization or an atmospheric pressure photoionization source, followed by linear discriminant analysis of the mass spectral data, oil samples corresponding to eight different botanical origins were perfectly classified with an excellent resolution among all the categories. An excellent correlation between the sterol profiles obtained by MS and by the official gas chromatography (with flame ionization detection) method was obtained. Thus, the proposed method is a promising alternative for sterol fingerprinting of vegetable oils, with the advantage that prior chromatographic separation is not required.

Superheated water extraction of cholesterol from solid food

A method based on superheated water extraction has been developed for the removal of cholesterol from solid food thus providing a clean approach by avoiding the use of organic solvents. A preconcentration step was also studied with the aim of solving the problem derived from low-cholesterol-content samples and dilution effect. The research also involved the optimisation of the parameters affecting the extraction process by a central composite experimental design as well as a univariate study of the optimisation of the preconcentration step. The time required for total removal of the target compound was 60 min. The method was validated using a certified reference material (NIST-CRM 1845) and was used to analyse food samples within a wide range of cholesterol concentrations. The efficiency for the CRM was 105%. The precision of the method yielded values less than 6.5% (expressed as relative standard deviation) in all instances.

Chromatographic analysis of minor constituents in vegetable oils

The main group of minor constituents belonging to vegetable oils are reviewed. Their importance in the characterization, origin and detection of oil mixtures are considered. Also, the determination of these minor components is of great value in establishing the oil quality and their genuineness. The most commonly used procedures (including the Official methodologies) normally applying chromatographic techniques are reviewed. The interference of each component within the determination of the other minor constituents are discussed. Furthermore, novel procedures for determining those compounds are also presented.