No abstract

Nonvolatile triacylglyceride (TAG) oxidation products play an important role in the oxidative degradation of lipids. They serve as a reservoir of oxygen-containing species and hence can act as off-flavor precursors or as initiators for further oxidation reactions. Possible nonvolatile lipid oxidation products are TAG with a hydroperoxy, hydroxy, epoxy, or oxo (ketone or aldehyde) group or combination of these groups. The breakdown of TAG hydroperoxides yields nonvolatile glyceride species with two intact fatty acid chains and one short chain mostly ending in an aldehyde or hydroxy group (2 1 / 2 glycerides). By means of normal-phase high-performance liquid chromatography (HPLC) with mass spectrometric (MS) detection, nonvolatile lipid oxidation products can be separated according to polarity. This results in separation into classes of TAG oxidation products, such as epoxy-TAG, oxo-TAG, hydroperoxy-TAG, hydroxy-TAG and 2 1 / 2 glycerides, which can be identified using selected ion chromatograms. The retention times of TAG oxidation products on the normal-phase HPLC system and the signal intensity of the MS detector are stable enough to enable quantitative analysis based on external calibration. The normal-phase HPLC-MS method is very suitable for the characterization and quantitation of nonvolatile TAG oxidation products in oxidized TAG reference compounds as well as in real oils or oil phases isolated from emulsions, spreads, or other fat-based food products. This method can give detailed information for the study of lipid oxidation mechanisms.

Plant sterols are added as their FA esters to vegetable oil table spreads at levels of approximately 8% as a means to reduce blood cholesterol levels. A new chromatographic method was designed to quantify quickly the level of plant sterol FA esters in incoming (raw) materials and to monitor their processing and final product quality with respect to total sterol level. The method shows a significant improvement in elapsed time and thus labor cost over the classical methods for sterols published in normative references. This improvement was obtained together with high performance characteristics, as shown by the internal method validation for recovery and repeatability. Its validity and robustness were further tested and confirmed in an international collaborative test. The method allows monitoring of sterol content of raw materials, fat-blends, and consumer products at the target level, with a range of 10% or less around this target. The calculated within-and betweenlaboratory reproducibility were 0.680 and 1.194 w/w%, respectively, for sterol-containing spreads. The results afforded by this method can be used for setting tight product specifications or to monitor trade between companies. We propose to add this new and fast method for total 4-desmethyl sterol(s) to analytical method collections as an adjunct to methods already listed for more detailed sterol analysis.Plant sterols (PS) and plant sterol FA esters (PSE) are recognized for their therapeutic efficacy in lowering blood cholesterol levels. Recent reviews on the pharmacological properties of PS and their fully saturated isomers (stanols) focus on this cholesterol-lowering effect (1,2). The blood cholesterol-lowering (BCL) effect of sterols, in particular the 4-desmethyl sterol(s) such as sitosterol, has been known since the 1950s. With the use of the FA esters instead of the free PS, a wider range of formulation options exists. The new interest and formulation options have resulted in a range of consumer products, such as vegetable-oil table spreads, designed to lower total blood cholesterol and LDL-cholesterol (3). The normal daily intake of about 20 g of a vegetable fat spread containing 8% PS, equivalent to 13-14% PSE, reduces the LDL-cholesterol by about 10% (4). With the use of PS and PSE at these elevated levels, these natural edible oil constituents have become functional food ingredients. Sterols used for the BCL effect are mixtures of mainly 4-desmethyl sterol(s) (sitosterol, campesterol, stigmasterol, and brassicasterol).To support quality control of raw materials, processing, and final consumer product control at these levels, a new and fast total sterol analysis for the content of mainly 4-desmethyl sterol(s) has been developed, validated, and collaboratively tested. The method is designed for a total content of these 4-desmethyl sterol(s) in a range of approximately 15-20% for vegetable oil blends, 8% in consumer products such as spreads, and approximately 60% in PSE concentrates. A new method was necessary because current analytical methods...

Triacylglyceride hydroperoxides (HPO-TAG), the primary autoxidation products of triacylglycerides (TAG), have been analyzed in polyunsaturated vegetable oils by means of nonaqueous reversed-phase high-performance liquid chromatography (HPLC) with ultraviolet detection. Using a retention time model based on equivalent carbon numbers, mono-and bishydroperoxy TAG and hydroxy TAG could be identified. The correlation between the peroxide value (POV) determined by iodometric titration and quantitative HPLC results for HPO-TAG was established for sunflower oil samples with POV between 0.5 and 50 meq/kg. The recovery of HPO-TAG in the HPLC procedure was found to be close to 100% in the POV range of 4 to 71 meq/kg. Absolute quantitative results for HPO-TAG in sunflower oil samples could not be obtained accurately, as molar extinction coefficients of HPO-TAG occurring in natural oils deviate from those of available HPO-TAG reference compounds.The oxidation of polyunsaturated lipids has received great attention due to increased consumption of vegetable oils with high unsaturation levels. Polyunsaturated lipids are oxidatively more labile than saturated and monounsaturated lipids and undergo autoxidation and photooxidation easily in the presence of initiators. Following a free radical chain mechanism, triacylglyceride hydroperoxides (HPO-TAG) are formed as primary products of triacylglyceride (TAG) oxidation. It is well established that HPO-TAG readily decompose into a wide range of aldehydes, ketones, hydrocarbons, and other volatile compounds which contribute to the flavor deterioration of lipid-containing food.Extensive oxidation experiments with subsequent analysis of the oxidation products using pure fatty acids and TAG as well as real oils have been carried out in order to elucidate the mechanism of lipid oxidation. For oxidation studies of vegetable oil TAG, triolein, trilinolein (LLL), and trilinolenin were frequently used as model systems. The main autoxidation products of triolein and LLL were identified as mono-, bis-, and trishydroperoxides, which are formed by sequential oxygen addition (1,2). The monohydroperoxides of triolein are composed of 8-, 9-, 10-, and 11-isomers (3). Autoxidation of LLL yields a mixture of 9-and 13-hydroperoxides as primary products (2,3; Scheme 1). LLL produces, in addition to mono-, bis-, and trishydroperoxides, substantial amounts of hydroperoxy epidioxides. The monohydroperoxides are composed of 9-, 12-, 13-, and 16-hydroperoxides (3,4). The cyclic peroxides are composed of 9-and 16-hydroperoxy epidioxides (4).Numerous attempts have been made to analyze hydroperoxides with respect to the position of the hydroperoxy group on the fatty acid chain, the sn-position in the TAG molecule, and the number of hydroperoxy groups per TAG molecule or per fatty acid chain (1-5). Park et al. (5) compared normalphase high-performance liquid chromatography (NP-HPLC) and reversed-phase (RP) HPLC for the analysis of autoxidized LLL and some vegetable oils. NP-HPLC of oxidized LLL revealed the geometri...

An on-line LC-GC method for the analysis of mono-, di-, and triacylglycerols in vegetable oil methyl esters has been developed. The concentrations of these components have turned out to be key parameters for the quality of diesel fuel substitutes. Separation of all classes of acylglycerols from the fatty acid methyl ester matrix is achieved by LC after acetylation of the hydroxyl groups. The acylglycerol fraction is transferred on-line to GC, using the looptype interface and concurrent eluent evaporation. Quantification of mono-, di-, and triacylglycerols is performed by combining external calibration with internal standardization. Both recovery of the procedure and reproducibility of the quantitative results are evaluated.