Institut für Lebensmittelchemie

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Countercurrent chromatographic fractionation followed by gas chromatography/mass spectrometry identification of alkylresorcinols in rye
(2020) Hammerschick, Tim; Wagner, Tim; Vetter, Walter
Alkylresorcinols (5-alkyl-1,3-dihydroxybenzenes, ARs) are bioactive phenolic lipid compounds which are particularly abundant in rye and partly other cereals. In this study on ARs, whole rye grain extracts were gained with cyclohexane/ethyl acetate (46/54, w/w). Silylated extracts were used to develop a gas chromatography with mass spectrometry method in the selected ion monitoring mode (GC/MS-SIM) for the sensitive detection of conventional ARs along with keto-substituted (oxo-AR) and ring-methylated ARs (mAR) with 5-alkyl chain lengths of 14 to 27 carbon atoms and 0 to 4 double bonds in one run. Analysis was performed by countercurrent chromatographic (CCC) fractionation using the solvent system n-hexane/ethyl acetate/methanol/water (9/1/9/1, v/v/v/v). Subsequent GC/MS-(SIM) analysis of 80 silylated CCC fractions enabled the detection of 74 ARs in the sample. The CCC elution of the ARs followed the equivalent chain length (ECL) rule in which one double bond compensated the effect of two (additional) carbon atoms. Novel or rarely reported ARs were detected in virtually all classes, i.e. saturated AR (AR14:0), even-numbered monounsaturated AR isomers (AR16:1-AR26:1), triunsaturated ARs (AR25:3), oxo-ARs (AR17:0 oxo, AR19:1 oxo, AR21:2 oxo, AR23:2 oxo) and odd-numbered methyl-ARs (mAR15:0-mAR23:0). Positions of the double bonds of monounsaturated ARs and oxo-ARs were determined with the help of dimethyl disulfide (DMDS) derivatives.
Determination of mono- and diacylglycerols from E 471 food emulsifiers in aerosol whipping cream by high-performance thin-layer chromatography–fluorescence detection
(2020) Oellig, Claudia; Blankart, Max; Hinrichs, Jörg; Schwack, Wolfgang; Granvogl, Michael
Mono- and diacylglycerol (MAG and DAG) emulsifiers (E 471) are widely applied to regulate techno-functional properties in different food categories, for example, in dairy products. A method for the determination of MAG and DAG in aerosol whipping cream by high-performance thin-layer chromatography with fluorescence detection (HPTLC–FLD) after derivatization with primuline was developed. For sample preparation, aerosol whipping cream was mixed with ethanol, followed by the addition of water and liquid-liquid extraction with tert-butyl methyl ether. The sample extracts were analyzed by HPTLC–FLD on silica gel LiChrospher plates with n-pentane/n-hexane/diethyl ether (22.5:22.5:55, v/v/v) as mobile phase, when interfering matrix like cholesterol and triacylglycerols were successfully separated from the E 471 food additives. For quantitation, an emulsifier with known composition was used as calibration standard and the fluorescent MAG and DAG were scanned at 366/> 400 nm. Limits of detection and quantitation of 4 and 11 mg/100 g aerosol whipping cream were obtained for both monostearin and 1,2-distearin, respectively, and allowed the reliable quantitation of MAG and DAG from E 471 far below commonly applied emulsifier amounts. Recoveries from model aerosol whipping cream with 400 mg E 471/100 g were determined in a calibration range of 200–600 mg E 471/100 g sample and ranged between 86 and 105% with relative standard deviations below 7%. In aerosol whipping creams from the German market, E 471 amounts ranged between 384 and 610 mg/100 g.
Enrichment and structural assignment of geometric isomers of unsaturated furan fatty acids
(2023) Müller, Franziska; Conrad, Jürgen; Hammerschick, Tim; Vetter, Walter
Furan fatty acids (FuFAs) are valuable minor fatty acids, which are known for their excellent radical scavenging properties. Typically, the furan moiety is embedded in an otherwise saturated carboxyalkyl chain. Occasionally, these classic FuFAs are accompanied by low amounts of unsaturated furan fatty acids (uFuFAs), which additionally feature one double bond in conjugation with the furan moiety. A recent study produced evidence for the occurrence of two pairs of E -/ Z -uFuFA isomers structurally related to saturated uFuFAs. Here, we present a strategy that allowed such trace compounds to be enriched to a level suited for structure determination by NMR. Given the low amounts and the varied abundance ratio of the four uFuFA isomers, the isolation of individual compounds was not pursued. Instead, the entire isomer mixture was enriched to an amount and purity suitable for structure investigation with contemporary NMR methods. Specifically, lipid extracted from 150 g latex, the richest known source of FuFAs, was subsequently fractionated by countercurrent chromatography (CCC), silver ion, and silica gel column chromatography. Analysis of the resulting mixture of four uFuFAs isomers (2.4 mg in an abundance ratio of 56:23:11:9) by different NMR techniques including PSYCHE verified that the structures of the two most abundant isomers were E -9-(3-methyl-5-pentylfuran-2-yl)non-8-enoic acid and E -9-(3-methyl-5-pent-1-enylfuran-2-yl)nonanoic acid. Additionally, we introduced a computer-based method to generate an averaged chromatogram from freely selectable GC/MS runs of CCC fractions without the necessity of pooling aliquots. This method was found to be suitable to simplify subsequent enrichment steps.
GC/EI-MS method for the determination of phytosterols in vegetable oils
(2021) Schlag, Sarah; Huang, Yining; Vetter, Walter
Sterols are a highly complex group of lipophilic compounds present in the unsaponifiable matter of virtually all living organisms. In this study, we developed a novel gas chromatography with mass spectrometry selected ion monitoring (GC/MS-SIM) method for the comprehensive analysis of sterols after saponification and silylation. A new referencing system was introduced by means of a series of saturated fatty acid pyrrolidides (FAPs) as internal standards. Linked with retention time locking (RTL), the resulting FAP retention indices (RIFAP) of the sterols could be determined with high precision. The GC/MS-SIM method was based on the parallel measurement of 17 SIM ions in four time windows. This set included eight molecular ions and seven diagnostic fragment ions of silylated sterols as well as two abundant ions of FAPs. Altogether, twenty molecular ions of C27- to C31-sterols with 0–3 double bonds were included in the final method. Screening of four common vegetable oils (sunflower oil, hemp oil, rapeseed oil, and corn oil) enabled the detection of 30 different sterols and triterpenes most of which could be identified.
NMR and GC/MS analysis of industrial chloroparaffin mixtures
(2020) Sprengel, Jannik; Vetter, Walter
Chlorinated paraffins (CPs) are high-volume chemicals used worldwide in various industries as plasticizers, lubricants, and flame retardants. CPs are produced by chlorination of alkane mixtures which leads to complex products of thousands of homologs and congeners. Classic mass spectrometric analyses of CPs allow determining carbon chain lengths and degrees of chlorination while information on the substitution patterns cannot be derived. Therefore, we performed different one- and two-dimensional nuclear magnetic resonance spectroscopy (NMR) experiments, elemental analysis (EA), and gas chromatography coupled with electron capture negative ion mass spectrometry (GC/ECNI-MS) for the analysis of ten technical CP products with 42%, 52%, and 70% chlorine content from four producers. Slight differences in chlorine content but varying chain length compositions were observed for similarly labeled products from different manufacturers. Two-dimensional heteronuclear spectral quantum coherence (HSQC) measurements helped to evaluate ten structural elements in the products and confirmed the presence of geminal chlorine atoms in primary and secondary carbons in products with 70% chlorine. The variation of signal groups increased with increasing chlorine content of the products. Two-dimensional heteronuclear multiple bond coherence (HMBC) analysis of one sample and GC/ECNI-MS measurements indicated the presence of impurities (e.g., C9-CPs, iso-alkanes) in different technical CP products. These methods could in future allow for better distinction of CP mixtures, and an improved trace-back of environmental CPs to the source, based on specific structural features. Additionally, further structural characterization could help in the development of more accurate analysis processes.

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