Prediction of gas chromatographic retention of polyunsaturated fatty acid methyl esters

Tutorial for the Characterization of Fatty Acid Methyl Esters by Gas Chromatography with Highly Polar Capillary Columns

The fatty acid composition of fats and oils is commonly determined by gas chromatography after preparing fatty acid methyl esters (FAME). Capillary columns coated with polyethylene glycol emerged as the preferred separation tool for the quantification of the polyunsaturated fatty acids contained primarily in marine oils. However, their selectivity is inadequate for measuring the trans fatty acids (TFA) contained in refined vegetable oils, dairy fats, and marine oils. Highly polar 100% poly(biscyanopropyl siloxane) capillary columns provide the necessary selectivity, but small differences in the phase polarity caused by column age, conditioning, or manufacturing variations affect the reproducibility of their separations of these complex samples. In this study, a simple procedure is described to compensate for small variations in column selectivity by adjusting the elution temperature. The balance between the dipole-induced dipole interactions and dispersive interactions was determined by measuring selectivity factors [SF(i)] corresponding to the elution of an unsaturated FAME such as 18:3n-3 relative to two saturated FAME such as 20:0 and 22:0. Knowing the SF(i) provided by the installed capillary column at a given elution temperature, and the SF(i) of the target separation, we propose a simple calculation to determine the necessary elution temperature adjustment to achieve (or restore) the desired separation. After determining the SF(i) which provides the optimal separation of TFA, the novel methodology was applied to the separation of refined vegetable oils, butter fats, and marine oils.

Palm oil wastes as feedstock for lipase production by Yarrowia lipolytica and biocatalyst application/reuse

Palm oil production chain generates a greasy residue in the refining stage, the Palm Oil Deodorizer Distillate (PODD), mainly composed of free fatty acids. Palm oil is also used industrially to fry foods, generating a residual frying oil (RFO). In this paper, we aimed to produce lipase from palm agro-industrial wastes using an unconventional yeast. RFO_palm, from a known source, consisted of 0.11% MAG + FFA, 1.5% DAG, and 97.5 TAG, while RFO_commercial, from a commercial restaurant, contained 6.7% of DAG and 93.3% of TAG. All palm oil wastes were useful for extracellular lipase production, especially RFO_commercial that provided the highest activity (4.9 U/mL) and productivity (465 U/L.h) in 75 h of processing time. In 48 h of process, PODD presented 2.3 U/mL of lipase activity and 48.5 U/L.h of productivity. RFO_commercial also showed the highest values for lipase associated to cell debris (843 U/g). This naturally immobilized biocatalyst was tested on hydrolysis reactions to produce Lipolyzed Milk Fat and was quite efficient, with a hydrolysis yield of 13.1% and 3-cycle reuse. Therefore, oily palm residues seem a promising alternative to produce lipases by the non-pathogenic yeast Y. lipolytica and show great potential for industrial applications.

Use of Yarrowia lipolytica Lipase Immobilized in Cell Debris for the Production of Lipolyzed Milk Fat (LMF)

Lipase immobilized on Yarrowia lipolytica cell debris after sonication of yeast cells (LipImDebri) was used in hydrolysis reaction as a novel strategy to produce lipolyzed milk fat (LMF). Extracellular (4732.1 U/L), intracellular (130.0 U/g), and cell debris (181.0 U/g) lipases were obtained in a 4 L bioreactor using residual frying oil as inducer in 24 h fermentation process. LipImDebri showed a good operational stability retaining 70% of lipolytic activity after the second cycle and 40% after the fourth. The highest degree of hydrolysis (28%) was obtained with 500 mg LipImDebri for 6 h of lipolysis of anhydrous milk fat. LMF produced with LipImDebri presented high contents of oleic (35.2%), palmitic (25.0%), and stearic (15.4%) acids and considerable amounts of odor-active short and medium chain fatty acids (C:4⁻C:10) (8.13%).

Trans fatty acid analyses in samples of marine origin: the risk of false positives

At conditions commonly applied for trans fatty analyses by gas chromatography, fatty acids naturally occurring in marine lipids may overlap chromatographically with C16 and C18 trans fatty acids and lead to false positives. Elution patterns were studied by tracking retention indices at shifting temperature conditions on two cyanopropyl-coated capillary columns. Most overlaps can be avoided by selecting the right chromatographic conditions, but it was not possible to find a single condition that eliminates the risk of overlap between trans fatty acids and interferents. In total, 17 compounds were identified as potential interferents, and the amounts of these compounds were quantified in various samples of marine origin. The interferents that will most likely contribute to incorrect assessments of trans fatty acids in marine lipids are probably 18:3 n-4 and 18:1 n-11.

Creating a fatty acid methyl ester database for lipid profiling in a single drop of human blood using high resolution capillary gas chromatography and mass spectrometry

Capillary gas chromatography (CGC) in combination with mass spectrometry (MS) was optimized for the separation and detection of the fatty acids occurring in the lipid fraction of blood. A fingertip blood sample (ca. 50 microL) was transesterified into the methyl esters and analyzed on a 100 m x 0.25 mm ID column coated with a biscyanopropyl polysiloxane (HP-88) stationary phase. The method was retention time locked. Programmed temperature vaporization injection (PTV) in the solvent venting mode was applied to minimize the sample size, while maintaining high sensitivity. The total analysis time was ca. 60 min. Retention times and both electron impact (EI) and positive chemical ionization (PCI) mass spectrometry were combined to elucidate the fatty acids according to alkyl chain, degree of unsaturation and position of the double bonds. Using extracted ion chromatograms about 100 fatty acids and related compounds were detected in blood samples and most of them were identified. This work resulted in a very large fatty acid methyl esters database, containing retention time and mass spectral information that will be applied to metabolomic studies.

Quantitative structure-(chromatographic) retention relationships

Since the pioneering works of Kaliszan (R. Kaliszan, Quantitative Structure-Chromatographic Retention Relationships, Wiley, New York, 1987; and R. Kaliszan, Structure and Retention in Chromatography. A Chemometric Approach, Harwood Academic, Amsterdam, 1997) no comprehensive summary is available in the field. Present review covers the period of 1996-August 2006. The sources are grouped according to the special properties of kinds of chromatography: Quantitative structure-retention relationship in gas chromatography, in planar chromatography, in column liquid chromatography, in micellar liquid chromatography, affinity chromatography and quantitative structure enantioselective retention relationships. General tendencies, misleading practice and conclusions, validation of the models, suggestions for future works are summarized for each sub-field. Some straightforward applications are emphasized but standard ones. The sources and the model compounds, descriptors, predicted retention data, modeling methods and indicators of their performance, validation of models, and stationary phases are collected in the tables. Some important conclusions are: Not all physicochemical descriptors correlate with the retention data strongly; the heat of formation is not related to the chromatographic retention. It is not appropriate to give the errors of Kovats indices in percentages. The apparently low values (1-3%) can disorient the reviewers and readers. Contemporary mean interlaboratory reproducibility of Kovats indices are about 5-10 i.u. for standard non polar phases and 10-25 i.u. for standard polar phases. The predictive performance of QSRR models deteriorates as the polarity of GC stationary phase increases. The correlation coefficient alone is not a particularly good indicator for the model performance. Residuals are more useful than plots of measured and calculated values. There is no need to give the retention data in a form of an equation if the numbers of compounds are small. The domain of model applicability of models should be given in all cases.

Focused microwave-assisted Soxhlet extraction of acorn oil for determination of the fatty acid profile by GC–MS. Comparison with conventional and standard methods

A study of the feasibility of focused microwave-assisted Soxhlet extraction of acorn oil and comparison of results from analysis of trans fatty acids in the oil thus obtained with those for oils obtained by use of other methods commonly used for oil extraction are reported here. The proposed method was optimized by means of a 21-experiment screening design to determine, by means of a reduced number of experiments, which factors affect both extraction efficiency and the degree of unsaturation of the fatty acids in the oil. The proposed method enables total extraction of the fatty acids in 30 min, which is much less than the time required by the Folch (4.5 h), Soxhlet (16 h), and ISO (8 h) reference methods and the stirring-extraction method (56 h). The efficiency of extraction achieved by use of the proposed method is statistically equivalent to that achieved by use of the other methods; the composition of the extracts obtained by use of the proposed method and the Folch and stirring reference methods are also statistically similar. No trans fatty acids were present in the extracts obtained by use of the Folch, stirring, and proposed methods but they were detected in the extracts obtained by use of both the Soxhlet and ISO methods.

Prediction of equivalent chain lengths from two-dimensional fatty acid retention indices

A recently introduced two-dimensional fatty acid retention index system (2D-FARI) was used as basis for prediction of equivalent chain lengths (ECL) of fatty acid methyl esters (FAME) on a BPX-70 stationary phase. Models for the relationship between 2D-FARI data and ECL values of a calibration sample with 30 common fatty acids were established by a simple multivariate regression. The models were thereafter applied on 2D-FARI data for other FAMEs and used to predict the ECLs for these compounds. The 2D-FARI values for the fatty acids in the calibration sample are given by definition. Thus, the only information necessary to calculate the ECL value for a compound run under identical conditions as the calibration sample is the 2D-FARI values for the compound, which can be acquired from literature data. The method was validated with test sets analysed with different temperature and flow programs. ECLs of various marine FAME and trans isomers of Eicosapentaenoic and Docosahexaenoic acid were predicted with root mean squared error of prediction from 0.002 to 0.012 ECL units.