Svetlana Momchilova

Quantitative TLC and Gas Chromatography Determination of the Lipid Composition of Raw and Microwaved Roasted Walnuts, Hazelnuts, and Almonds

Abstract Analytical and preparative thin‐layer chromatography (TLC) on intact silica gel and silica gel layers modified with either silver nitrate (Ag‐TLC) or dimethyldichlorosilane (RP‐TLC), combined with densitometric quantification and gas chromatography (GC), have been used to elucidate the lipid classes, their fatty acid profiles, the triacylglycerol, and sterol compositions of raw and microwaved roasted walnuts, hazelnuts and almond kernels harvested in Bulgaria. The results on fatty acid and triacylglycerol compositions are in good agreement with those reported for other geographical regions. Microwave roasting on full power for 3 min produced ready‐to‐consume kernels and no changes in lipids were detected. The combination of TLC techniques used for identification and quantification of triacylglycerols gave results comparable with those obtained using reversed phase liquid chromatography‐mass spectrometry (LC‐MS).

Fatty acid composition of wild mushroom species of order Agaricales—Examination by gas chromatography–mass spectrometry and chemometrics

Applying gas chromatography-mass spectrometry of 4,4-dimethyloxazoline fatty acid derivatives, the fatty acid composition of 15 mushroom species belonging to 9 genera and 5 families of order Agaricales growing in Bulgaria is determined. The structure of 31 fatty acids (not all present in each species) is unambiguously elucidated, with linoleic, oleic and palmitic acids being the main components (ranging between 70.9% (Marasmius oreades) and 91.2% (Endoptychum agaricoides)). A group of three hexadecenoic positionally isomeric fatty acids, 6-, 9- and 11-16:1, appeared to be characteristic components of the examined species. By applying chemometrics it was possible to show that the fatty acid composition closely reflects the classification of the species.

Determination of Petroselinic, cis-Vaccenic and Oleic Acids in Some Seed Oils of the Umbelliferae by Silver Ion Thin Layer Chromatography of their Phenacyl Esters

A method is proposed for the determination of petroselinic, oleic and cis-vaccenic acids in plants of the Umbelliferae by using silver ion thin layer chromatography and densitometry. The fatty acids are first converted into phenacyl esters and this enables base line separation at ambient temperature on a plate impregnated with 1% methanolic silver nitrate. Conditions were found for the simultaneous determination of the saturated and dienoic fatty acids while maintaining the resolution of petroselinic and oleic acids. The procedure is suitable for screening plants of the Umbelliferae in phytochemical and selection studies, and may be of value as a small-scale preparative technique.

TLC and GC‐MS Probes into the Fatty Acid Composition of some Lycoperdaceae Mushrooms

Abstract The efficiency of the successive application of TLC, GC‐MS of fatty acid methyl esters and GC‐MS of fatty acid 4,4‐dimethyloxazoline derivatives in examination of the complex fatty acid mixture in mushrooms is demonstrated on examples of four species of Lycoperdaceae family. Twenty seven fatty acids were unambiguously identified in Bovista plumbea, Calvatia utriformis, Lycoperdon perlatum, and Lycoperdon pyriforme, grown in Bulgaria. Linoleic (37–65%), oleic (7–24%), palmitic (12–18%), and stearic (2–6%) acids are the major components. The mushrooms contain a characteristic group of three isomeric hexadecenoic fatty acids (double bond in positions 6‐, 9‐, and 11‐), which are resolved and determined separately for the first time. The presence of 9‐icosenoic‐, 9,12‐icosadienoic‐, tricosanoic‐, pentacosanoic‐, hexacosanoic‐, and 11‐hexacosenoic acids is reported for the first time in Basidiomycetes.

Separation of isomeric octadecenoic fatty acids in partially hydrogenated vegetable oils as p -methoxyphenacyl esters using a single-column silver ion high-performance liquid chromatography (Ag-HPLC)

A protocol for separation of positionally isomeric trans- and cis-octadecenoic fatty acids as their p-methoxyphenacyl esters, using a single column silver ion high-performance liquid chromatography (Ag-HPLC) with UV detection, is described. The procedure involves hydrolysis of oil to free fatty acids, derivatization to p-methoxyphenacyl esters, purification and separation by Ag-HPLC. The procedure is robust and relatively rapid. In total, it takes about 16 h or overnight and a further 5 h to carry out. Its feature and value consist in the application of p-methoxyphenacyl esters in Ag-HPLC, thus ensuring excellent simultaneous separation of both configurational and positional fatty acid isomers on a single column by a single run. Quantification is not affected by the fatty acid structure, and the method is highly sensitive. As fatty acid isomerization is a strong evidence for adulteration of lipid-containing food products with chemically modified oils and fats, the procedure is especially appropriate for detection and authenticity analysis in many areas of food manufacturing and quality control.

Bioaccessibility of Cd, Cu, Fe, Mn, Pb, and Zn in hazelnut and walnut kernels investigated by an enzymolysis approach.

Bioaccessibility of four essential (Fe, Cu, Mn, Zn) and two toxic (Cd, Pb) elements in kernels of four walnut and four hazelnut cultivars was investigated using sequential enzymolysis approach and atomic absorption spectrometry. It was found that the assimilable part of elements was not dependent on nut cultivar. The bioaccessible fraction of Cu, Mn, and Zn was definitely higher for hazelnuts (62% Cu, 39% Mn, 58% Zn) than for walnuts (14% Cu, 21% Mn, 15% Zn). Bioaccessible Fe was 20-24% from its total content for both nut types. Solubility in the simulated intestinal juice is affected by both formation of stable soluble complexes and back sorption of dissolved elements on nut solid residues. Lead shows strong insolubility due to the high sorption affinity of lead ions to the insoluble fraction of nuts. Thus, walnuts and hazelnuts could act as effective biosorbents for lead detoxication.

Fatty Acids, Triacylglycerols, and Sterols in Neem Oil (Azadirachta Indica A. Juss) as Determined by a Combination of Chromatographic and Spectral Techniques

Abstract Quantitative thin‐layer chromatography in silver ion and reversed phase modes, gas chromatography, gas chromatography–mass spectrometry, and 13C nuclear magnetic resonance spectrometry were employed to determine the lipid composition in neem (Azadirachta indica A. Juss) kernel oil. Thirteen fatty acids and 25 triacylglycerols species were identified and quantified. The seven main triacylglycerols species were found in almost equal amounts in the range 7–10%. Saturated fatty moieties occupied positions 1‐ and 3‐ in the triacylglycerol molecule, oleic acid was almost equally distributed, and linoleic acid predominantly occupied position 2. Sitosterol, stigmasterol, campesterol, and fucosterol were the main components in free sterol and sterol ester fractions.

Quantitative Silver Ion Thin Layer Chromatography of Triacylglycerols from Sunflower Oils Differing in the Level of Linoleic Acid

Abstract Eight samples of sunflower oil with different linoleic acid contents (9–63{%}) were subjected to a triacylglycerol (TAG) analysis by silver-ion thin-layer chromatography with densitometric quantification. In spite of this substantial change in the fatty acid composition, the relative content of the component TAG classes in the sum of polyunsaturated triacylglycerols remains constant. Thus, a characteristic fingerprint of sunflower oil TAG has been outlined. It is not affected by the linoleic acid content and might be of use in authenticity and adulteration control of sunflower and olive oils.

Cyclohexanediol Fatty Acid Diesters as Model Compounds for Mechanistic Studies in Silver Ion High Performance Liquid Chromatography

Abstract Series of cis‐1,2‐ and cis/trans‐1,4‐cyclohexanediol diesters of saturated, oleic and linoleic fatty acids were employed as model compounds in a study of the effect of the unsaturation and the position of the acyl moieties on the retention of acylglycerol molecules in silver ion high‐performance liquid chromatography (HPLC). cis‐1,2‐Diunsaturated cyclohexanediol diesters were retained slightly more strongly than were the respective cis/trans‐1,4‐compounds, thus indicating that formation of chelate‐type complexes between silver ions and the double bonds of two adjacent unsaturated fatty acid residues during silver ion chromatography may occur to a limited extent.

Enhanced cell surface hydrophobicity favors the 9α-hydroxylation of androstenedione by resting Rhodococcus sp. cells

The achievement of an effective process of 9α‐hydroxylation of 4‐androstene‐3,17‐dione is of significant importance as it leads to the formation of the key intermediate 9α‐hydroxy‐4‐androstene‐3,17‐dione which is not possible by chemical means. In this study, the 9α‐hydroxylation of 4‐androstene‐3,17‐dione was carried out by resting Rhodococcus sp. cells. The ability of the naturally hydrophobic Rhodococcus to assimilate n‐alkanes was employed to obtain a cell depot with an intentionally increased cell surface hydrophobicity. The control Rhodococcus sp. cells were cultivated on medium containing glucose instead of n‐alkanes as a source of carbon and energy. Cells were harvested, washed from the cultivation media, and subjected to transformation of crystal androstenedione in buffer medium. The hydrophobicity of the n‐alkanes‐ and glucose‐grown cells, their total lipid content, and fatty acid composition were determined. The ultrastructure of the n‐alkanes‐ and glucose‐grown cells and their steroid hydroxylating activities were examined and compared. The results obtained in the present study showed that the intentionally achieved growth‐driven enhancement of the already hydrophobic Rhodococcus sp. cells made them even more compatible with the hydrophobic steroid substrate and enhanced its accessibility, which provided an increased steroid hydroxylating activity and lack of the accompanying product destruction.