Elizabeth Y. Brechany

Mass spectra of the picolinyl esters of isomeric mono- and dienoic fatty acids

The picolinyl ester derivatives of the complete series of isomeric octadecenoates, methylene-interrupted octadecadienoates, and of octadec-9-ynoate have been subjected to gas chromatography-mass spectrometry. A fused-silica capillary column, coated with a cross-linked methyl silicone, was used for the separation. Electron impact spectra were determined at 70 eV. Earlier observations with a limited series of model compounds were confirmed, and it was shown that the picolinyl ester derivatives were of almost universal value in the location of double bonds in such isomers. Difficulties of interpretation arose mainly when the double bonds were close to the carboxyl group.

A comparison of pyrrolidide and picolinyl ester derivatives for the identification of fatty acids in natural samples by gas chromatography-mass spectrometry.

The pyrrolidide and picolinyl ester derivatives of the fatty acids in two natural lipid samples rich in unsaturated fatty acids, pig testis lipids and cod liver oil were satisfactorily resolved on capillary columns of fused silica coated with stationary phases of varying polarity. The picolinyl esters, in particular, when subjected to gas chromatography-mass spectrometry on a column containing a cross-linked methyl silicone, gave distinctive mass spectra, which could be interpreted in terms of both the numbers and positions of the double bonds.

Comparison of the microbiological, compositional, biochemical, volatile profile and sensory characteristics of three Italian PDO ewes’ milk cheeses

Abstract Three batches of three Italian ewes’ milk cheeses (Canestrato Pugliese, Fiore Sardo and Pecorino Romano), which were manufactured under the Protected Denomination of Origin (PDO), were compared for microbiological, compositional, biochemical, volatile profile and sensory characteristics. After ca. 1 year of ripening, the three cheeses had a complex microbial population, composed mainly of non-starter lactic acid bacteria (NSLAB); several species of mesophilic lactobacilli and enterococci were identified. Pecorino Romano had a very high level of NaCl, 8.7±0.1% w/w. The level of pH 4.6-soluble nitrogen increased in the order: Canestrato Pugliese>Fiore Sardo>Pecorino Romano. Urea-PAGE electrophoresis showed that the hydrolysis of α s1 -casein was more consistent than β -casein. RP-HPLC profiles of the ethanol-soluble and ethanol-insoluble fractions of the pH 4.6-soluble nitrogen showed differences between the cheeses which agreed with the content of free amino acids. Glutamic acid, histidine, valine, isoleucine, leucine and phenylalanine were the free amino acids present at the highest levels in all the cheeses. Sixty-two volatile components were identified by Gas Chromatography-Mass Spectrometry analysis of steam distillates of the cheeses. The volatile profile of the three cheeses differed significantly. Esters were the main volatiles in the Canestrato Pugliese cheese but were the lowest in Fiore Sardo cheese. Ketones and alcohols were the principal class of volatile components in Fiore Sardo and Pecorino Romano cheeses, respectively. Lactones and products of the breakdown of the sulphur-containing amino acids were found at considerable levels in all cheeses, but aldehydes were present at low levels. Only 30 carboxylic acids were identified; Canestrato Pugliese had the highest content of total acids. Butanoic, hexanoic, octanoic and decanoic acids represented the 30–33% of the total carboxylic acids in the cheeses. The cheeses were subjected to descriptive sensory analysis; 19 discriminating and 2 descriptive attributes were analysed by Principal Component Analysis (PCA). The sensory characteristics of the three ewes’ milk cheeses were distinct.

Enhancement of amino acid catabolism in Cheddar cheese using α-ketoglutarate : amino acid degradation in relation to volatile compounds and aroma character

The effectiveness of the transaminase acceptor α-ketoglutarate in enhancing amino acid catabolism and manipulating the aroma profile of Cheddar cheese has been studied. Utilisation of α-ketoglutarate, catabolism of amino acids, volatiles production, and aroma profile of the cheese were monitored after 6, 12 and 24 weeks ripening. Glutamate and GABA were considerably enhanced on addition of the transaminase acceptor while levels of phenylalanine, leucine, isoleucine, alanine, valine, methionine and threonine were reduced. Addition of α-ketoglutarate increased volatile components originating from the catabolism of branched chain and aromatic amino acids. These compounds included acetic, propanoic, 2-methylpropanoic and 3-methylbutanoic acids, 3-methylbutanol, phenylacetaldehyde and benzaldehyde. Additionally enhanced production of 3-OH-2-butanone was evident. Addition of α-ketoglutarate increased aroma intensity, creamy and fruity aromas. Effects obtained must be verified by tasting cheeses made with food grade α-ketoglutarate, but results suggest potential benefits in accelerated maturation, low fat systems and manipulation of flavour profiles.

Fatty acid composition of some algae from the black sea

Abstract The fatty acid compositions were determined of two marine algae of the Rhodophyceae, one of the Phaeophyceae and four of the Chlorophyceae, from the Black Sea in Bulgaria. The results may be of value for taxonomic purposes.

Silver ion high-performance liquid chromatography and gas chromatography—mass spectrometry in the analysis of complex fatty acid mixtures: application to marine invertebrates

Abstract High-performance liquid chromatography on a stable silver ion column permitted the isolation of clean fractions differing in degree of unsaturation, with zero to six double bonds, of the methyl ester derivatives of fatty acids from complex lipid samples. By a combination of gas chromatographic analysis of the methyl esters on capillary columns coated with polar phases, and gas chromatography-mass spectrometry of the picolinyl ester derivatives, separated on non-polar phases, most components can be identified. In order to demonstrate the methodology, fatty acids from the Black Sea invertebrates Mytilus galloprovincialis and Rapana thomasiana were separated into 41 and 46 defined components, respectively (58 different fatty acids in total), and full quantitative analyses were achieved of most constituents present at levels of about 0.1% of the total and above. The fatty acids found included mono- and multi-methyl branched isomers, mono- and polyunsaturated fatty acids of the (n-1), (n-3), (n-4), (n-5), (n-6), (n-7), (n-8), (n-9), (n-11) and (n-13) families, and dienoic acids with several methylene groups between the double bonds, ranging in chain length from C13 to C22.

Silver ion chromatography and gas chromatography-mass spectrometry in the structural analysis of cyclic dienoic acids formed in frying oils

The nature of the cyclic monoenoic fatty acids formed from linoleic acid in sunflower oil heated to 275°C has been determined by gas chromatography-mass spectrometry of the picolinyl ester derivatives, before and after hydrogenation and deuteration, and following simplification by silver ion high-performance liquid chromatography. In addition, they were examined by gas chromatography-Fourier transform infrared spectroscopy. Cyclopentene fatty acids (50% of the total monoenes) were formed from C-8 to C-12 and C-10 to C-14 of the original chain in equal amounts with unique stereochemistry. In some isomers the double bond appeared to remain in its original position, and in others it migrated to a substituted ring carbon. Isomers (25% of the total monoenes) were formed with a cis double bond in position 9 or 12 in equal amounts, and either a cyclopentane ring involving C-5 to C-9 or C-13 to C-17 or a cyclohexane ring involving C-5 to C-10 or C-12 to C-17 of the original fatty acid chain. With these compounds, most if not all of the possible configurational isomers were produced. Related compounds (25% of the total monoenes) with a trans double bond in position 9 or 12 were found with only six-membered rings with a restricted stereochemistry. Some bicyclic fatty acids were also present in the mixture.

The fatty acids of the spongeDysidea fragilis from the black sea

The fatty acid composition of the sponge,Dysidea fragilis, from the Black Sea has been determined by analytical gas chromatography, silver ion high-performance liquid chromatography and gas chromatography/mass spectrometry. More than a hundred different fatty acids were identified, of which many were similar to those in sponges from tropical seas. On the other hand, some of the fatty acids identified have not been found previously in sponges or other marine sources and perhaps are new to science. These include 13-methyl-tetradec-4-enoic and 14-methyl-hexadec-6-enoic acids, together with demospongic acids,i.e. 5,9,17-tetracosatrienoic, 5,9,17-pentacosatrienoic and 5,9,19-pentacosatrienoic acids. From the elution behavior on silver nitrate chromatography, all the double bonds were of thecis-configuration.

Distribution and biosynthesis of stearidonic acid in leaves of Borago officinalis

Abstract An octadecatetraenoic acid was present as a major fatty acid component of the leaf lipids of borage. Gas chromatography-mass spectrometry of its picolinyl esters gave unsaturation centres at carbons Δ 6 , Δ 9 , Δ 12 , and Δ 15 and confirmed its identity as stearidonic acid (SDA; octadecatetraenoic acid, C18:4, Δ 6,9,12,15 . The chloroplast galactolipids, monogalactosyldiacyglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) were particularly rich in SDA. SDA was absent, howver, from the plastid phospholipid, phosphatidylglycerol (PG). Stereochemical analysis of the fatty acids in leaf MGDG and phosphatidylcholine (PC) showed that both SDA and γ-linolenic acid (GLA) were almost exclusively located at carbon sn -2 of these complex lipids. In time-course studies with excised seed cotyledons induced to green by light treatment, SDA appeared in the galactolipids before its detection in PC suggesting that its major site of synthesis in the leaf was prokaryotic and largely located in the chloroplasts. Borage seed microsomes, which have high Δ 6 desaturase ( Δ 6 des) activity, catalysed the synthesis of SDA from exogenously supplied α-linolenic acid (ALA). Linseed cotyledons which have an active Δ 15 des, on the other hand, could not convert exogenously supplied GLA to SDA. These observations suggest that SDA is formed from ALA via Δ 6 des activity at carbon sn-2 of MGDG and not from GLA and subsequent Δ 15 -desaturation.

Characterization of wax esters in the roe oil of amber fish,Seriola aureovittata

The wax esters of the roe oil of the amber fish,Seriola aureovittata, have been resolved by high-performance liquid chromatography (HPLC) in the silver-ion mode. Each of the fractions collected was transmethylated, and the fatty acids and alcohols were identified by gas chromatography/mass spectrometry (GC/MS) as the picolinyl esters and nicotinates, respectively. Their compositions were determined by GC. The fatty acid composition is complex, and the main components are C18:1n-9 (35.5 mol%), C22:6n-3 (20.3 mol%), and C16:1n-7 (10.7 mol%), while fatty alcohols are limited to saturated (C16:0, 60.3 mol%; C18:0, 15.3 mol%; C14:0, 5.1 mol%) and monoenoic alcohols (C18:1n-9, 6.5 mol%; C16:1n-7, 4.5 mol%) with traces (<0.1 mol%) of polyunsaturated fatty alcohols such as C20:3n-3, C20:4n-6, C20:5n-3, and C22:5n-3. Silver-ion HPLC exhibited excellent resolution in which fractions were resolved on the basis of the number and configuration of double bonds as well as the distribution pattern between the acid and alcohol moieties of the molecules with a given number of double bonds. The main wax ester fraction are those of monoenoic acid-saturated alcohol species, hexaenoic acid/saturated alcohol species, and pentaenoic acid/saturated alcohol species. Appreciable specificity was observed in the esterification of fatty acids with alcohols, and surprisingly, no saturated acid-monoenoic alcohol species were detected.