M.C. Pérez-Camino

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.

Gas and liquid chromatography of hydrocarbons in edible vegetable oils.

Hydrocarbons, an important part of the minor constituents belonging to vegetable oils are reviewed. Their importance, origin, characterization and detection in edible vegetable oils are considered. The determination of some of them as a means of establishing oil quality and genuineness is also highlighted. The official methodologies, as well as the most commonly procedures used for isolation and analysis are reviewed. Furthermore, novel procedures applying new techniques for determining those compounds are also presented.

Digestibility of fatty acid monomers, dimers and polymers in the rat

This study was designed to determine digestibilities of fatty acid monomers, dimers and polymers as components of diets containing thermally oxidized oils. Male Wistar rats were fed semipurified diets supplemented with unheated, heated and a 1:1 mixture of unheated/heated olive oils at 6, 12 and 20% w/w of diet. In a 14-d experimental period, fecal lipids were extracted and analyzed by a combination of adsorption and high-performance size-exclusion chromatographies. Thus, it was possible to separate and quantitate five groups of fatty acids—nonpolar monomers, oxidized monomers, nonpolar dimers, oxidized dimers and polymers. Nonpolar fatty acid monomers showed high digestibilities, although significantly influenced by the alteration level of the dietary oil. The apparent absorption of oxidized fatty acid monomers averaged 76.6%. Among polymeric fatty acids, the lowest digestibilities were found for nonpolar dimers (10.9% on average), whereas oxidized dimers and polymers possessed higher apparent absorbability than expected, ranging from 22.7% to 49.6%. Chemical modifications prior to absorption, leading to less complex products, may have contributed to enhanced digestibility of polymers.

Evaluation of Hydrolysis and Absorption of Thermally Oxidized Olive Oil in Non-Absorbed Lipids in the Rat

The aim of this study was to investigate the contribution of hydrolysis and absorption to the reduced digestibility found for heat-oxidized oils. Indirect evaluation methods were designed to assess the hydrolysis and absorption undergone in vivo, based on the analysis of non-absorbed lipids in faeces. The results indicated difficulties in the hydrolysis of complex glyceridic molecules included in heat-oxidized fats. Also, the data suggested that the extension of hydrolysis undergone in vivo was closely dependent on the amount and alteration degree of the dietary fat. This fact was clearly shown specifically for non-altered fatty acids while in the case of non-polar dimer fatty acids the low digestibility value may be associated in part to difficulties during the absorption process.

Simultaneous determination of long-chain aliphatic aldehydes and waxes in olive oils

A procedure for the simultaneous determination of long-chain aliphatic aldehydes, and aliphatic and triterpenic waxes in virgin olive oils is described. A fraction containing these compounds was isolated from the oil using solid-phase extraction on silica-gel cartridges. The fraction was analyzed by capillary GC on 35%-dimethyl-65%-diphenylpolysiloxane phase using on-column injection. In extra virgin olive oils, the long-chain aliphatic aldehydes with even carbon atom numbers from C22 to C30 were identified by comparison of retention times and mass spectra with those of synthesized standards. The concentration of total aldehydes ranged from 20.2 to 108.0 mg/kg-n-hexacosanal being the most abundant aldehyde. The determination of aliphatic waxes was achieved with similar or better precision than that of the EU official methods.

Fatty acid alkyl esters presence in olive oil vs. organoleptic assessment

The scientific work on the authenticity and quality of olive oil is an ever-growing area. Olive oil genuineness is not only valuable for the producers, but also for the consumers who expect an actual correspondence between the products they purchase and the information on the packaging labels. Sometimes oils rejection by consumers is just a matter of taste, sometimes is a more objective question. Low quality olive oils with weak organoleptic defects are the targets of illegal blends that can be detected by determining the content of fatty acid alkyl esters (FAAEs). In this line we have established a relationship between the FAAEs concentration of olive oils and their sensory classification. Besides, a connection between the presence of large quantities of FAAEs and fermentative organoleptic defects has been proven.

Determination of the molecular species composition of diacylglycerols in human adipose tissue by solid-phase extraction and gas chromatography on a polar phase

The free diacylglycerols (DAGs) in adipose tissue are involved in the metabolism of stored lipids and hence are related to the supply of fatty acids for other tissues. This paper describes a simple, fast, and reproducible method for the identification and quantification of different molecular species of DAGs in human adipose tissue. The method comprised solid-phase extraction on a diol-bonded phase column combined with capillary GC analysis of silylated DAG derivatives on a polar phase (65% phenylmethylsilicone). Separation of the DAGs was achieved based on chain length, isomeric structure (1,2- and 1,3-DAGs), and degree of unsaturation. The main DAGs were 1,2-OO, 1,2-OP, 1,2-LO and 1,2-LP. The composition was corroborated by analysis of the component fatty acids of the DAGs, 18:1(n-9), 16:0, and 18:2(n-6) being the three major fatty acids obtained.

Isolation and characterization of sucrose polyesters

Various chromatographic techniques for isolation and separation of highly esterified sucrose polyesters (SPE) of olive oil are described. High-performance size-exclusion chromatography was used to check the purity of the samples, particularly to show that SPE were free from unreacted fatty acid methyl esters. Thin-layer chromatography (TLC), Iatroscan TLC flame-ionization detection (FID) and highperformance liquid chromatography (HPLC) on reversed-phase were applied for separation of octa-, hepta- and hexaesters of sucrose. Pure fractions from the total mixture, obtained by column chromatography, were identified by infrared and nuclear magnetic resonance spectroscopy. When necessary, specific reactions were applied; particularly, silylation and lead acetate-dichlorofluorescein (in toluene) spray were used to ascertain the degee of esterification of sucrose. Finally, octa-, hepta- and hexaesters of sucrose were quantitated by silica column chromatography, TLC/FID and HPLC on reversed-phase.

Characterization of sucrose polyesters-triacylglycerols mixtures

High-performance size-exclusion chromatography (HPSEC) and thin-layer chromatography/flame-ionization detection (TLC/FID) have been used for the characterization of mixtures of either monoacid sucrose octaesters with triacylglycerols (TAG) or sucrose polyesters (SPE) prepared from oils with natural oils. In mixtures of monoacid sucrose octaesters/TAG, no significant differences were found between the values obtained by either HPSEC or TLC/FID and the actual component proportions. Additionally, components could be separated by TLC, which was confirmed by fatty acid composition data of each fraction. Analysis of SPE/oil mixtures was attainable by HPSEC, but alternative quantitation by TLC/FID required previous silylation. Likewise, fatty acid composition could be determined only in the total mixture and in the sucrose octaester fraction. A formula derived for calculation of oil fatty acid composition, based on analytical data, showed the validity of the approach used in this study to determine component proportions in functional SPE/oil mixtures.

Comparison of oxidation of sucrose octaesters and triacylglycerols derived from olive oil

Abstract Pure Sucrose Octaesters (SOE) and Triacylglycerols (TG) with the same fatty acid composition were oxidized at 100°C for 3, 6 and 12 h, in triplicate. Quantification of oxidized substrates and oxidized fatty acids was carried out by a combination of adsorption and size exclusion chromatographies. Induction time periods, peroxide values and changes in fatty acids were also determined. The results indicated that triacylglycerols were oxidized more rapidly than sucrose octaesters. No prooxidant effect of triacylglycerols on the oxidation of sucrose octaesters was found when a mixture (1:1) of both of them was subjected to oxidation.