André Grandgirard

Linoleic acid isomers in heat treated sunflower oils

Heat treatment of sunflower oil resulted in the formation of linoleic geometrical and positional isomers. These isomers were isolated using a combination of column chromatography, urea fractionation, high performance liquid chromatography (HPLC) on a C18 reverse phase column and silver nitrate thin layer chromatography (TLC). Each component was submitted to hydrazine reduction and the resulting monoenes to AgNO3-TLC. The resultingcis andtrans fractions were submitted to ozonolysis in BF3-MeOH in order to determine the position of the ethylenic bonds. The major isomers were thecis, trans andtrans, cis 18∶2 Δ9, 12, thetrans, trans 18∶2 Δ9, 12 and somecis, trans, trans, cis andtrans, trans 18∶2 conjugated dienes. Thecis, trans andtrans, cis conjugated dienes were the Δ9, 11, Δ10, 12, Δ11, 13 and Δ12, 14 while thetrans, trans isomers were the Δ9, 11, Δ10, 12 and Δ11, 13. These C18∶2 isomers also were detected in oils collected from restaurants and market vendors.

Oxyphytosterols are present in plasma of healthy human subjects

The oxidised derivatives of phytosterols (oxyphytosterols) were identified in plasma samples from thirteen healthy human volunteers, using MS. All the samples contained noticeable quantities of (24R)-5beta,6beta-epoxy-24-ethylcholestan-3beta-ol (beta-epoxysitostanol) and (24R)-ethylcholestan-3beta,5alpha,6beta-triol (sitostanetriol) and also trace levels of (24R)-5alpha,6alpha-epoxy-24-ethylcholestan-3beta-ol (alpha-epoxysitostanol), (24R)-methylcholestan-3beta,5alpha,6beta-triol (campestanetriol) and (24R)-ethylch olest-5-en-3beta-ol-7-one(7-ketositosterol). The amounts of these oxyphytosterols in plasma varied from 4.8 to 57.2 ng/ml. There are two possibilities concerning the origin of these compounds. First, they could come from the small amounts of oxyphytosterols in food. Second, they could originate from the in vivo oxidation of phytosterols in plasma. Very few data actually exist concerning these compounds. Their identification in human samples suggests that further research is necessary in this field.

Occurrence of geometrical isomers of eicosapentaenoic and docosahexaenoic acids in liver lipids of rats fed heated linseed oil

Monotrans geometrical isomers of 20∶5 n−3 and 22∶6 n−3 were detected in liver lipid of rats fed heated linseed oil. The isomers were identified as being 20∶5 δ5c, 8c, 11c, 14c, 17t and 22∶6 δ4c, 7c, 10c, 13c, 16c, 19t. These fatty acids were isolated as methyl esters by preparative high-performance liquid chromatography (HPLC) on reversed phase columns followed by silver nitrate thin layer chromatography (AgNO3-TLC). The structures were identified using partial hydrazine reduction, AgNO3-TLC of the resulting monoenes, oxidative ozonolysis of each monoene band, and gas-liquid chromatography (GLC) of the resulting dimethyl esters and monomethyl esters. Fourier-transform-infrared spectrometry confirmed thetrans geometry in isolated 20∶5 and 22∶6 isomers. The isomers of eicosapentaenoic and docosahexaenoic acids in liver lipids probably resulted from desaturation and elongation of 18∶3 δ9c, 12c, 15t, a geometrical isomer of linolenic acid present in the heated dietary oil.

Heat treatment of vegetable oils I. Isolation of the cyclic fatty acid monomers from heated sunflower and linseed oils

Linseed and sunflower oils were heated at 275 C for 12 hr under nitrogen. The sunflower oil was also heated in a commercial fryer at 200 C for 48 hr using a 2-hr daily cycle. The cyclic fatty acid monomers (CFAM) formed during the heat treatment of the linseed oil were isolated by a combination of saponification, esterification, column chromatography on silicic acid and urea fractionation. The isolated CFAM fraction was 99% pure, the balance being some 12:2ω6. Another step was necessary to isolate the CFAM from heated sunflower oils. The urea adduct fractionation resulted in the isolation of a nonurea adduct fraction which contained a mixture of CFAM and 18:2ω6. These were further separated using high performance liquid chromatography (HPLC) on a C18 reverse phase column. Each fraction was analyzed by gas liquid chromatography and hydrogenated to determine the content of the C18 straight chain fatty acids.

Heat treatment of vegetable oils. II. GC-MS and GC-FTIR spectra of some isolated cyclic fatty acid monomers

Gas liquid chromatography coupled with mass spectrometry (GC-MS) showed that the cyclic fatty acid monomers (CFAM) isolated from a heated linseed oil have two ethylenic bonds, while the CFAM isolated from heated sunflower oils were saturated and monoethylenic isomers. GC-MS studies also showed the presence of cyclohexenic derivatives in the case of linseed oil.GLC coupled with Fourier transform infrared spectrometry (GC-FTIR) studies indicated that the CFAM isolated from linseed oil were ofcis (Z),trans (E) structures except two components which werecis,cis (Z,Z) dienoic acids. The unsaturated CFAM isolated from sunflower oils werecis (Z) andtrans (E) monoethylenic isomers. For sunflower oils, the major CFAM were isomers having acis (Z) ethylenic bond. The saturated CFAM isolated from a heated sunflower oil had molecular weights of 296 and 294. The latter could correspond to some bicyclic isomers.

Incorporation oftrans long-chain n−3 polyunsaturated fatty acids in rat brain structures and retina

During heat treatment, polyunsaturated fatty acids and specifically 18∶3n−3 can undergo geometrical isomerization. In rat tissues, 18∶3 Δ9c, 12c, 15t, one of thetrans isomers of linolenic acid, can be desaturated and elongated to givetrans isomers of eicosapentaenoic and docosahexaenoic acids. The present study was undertaken to determine whether such compounds are incorporated into brain structures that are rich in n−3 long-chain polyunsaturated fatty acids. Two fractions enriched intrans isomers of α-linolenic acid were prepared and fed to female adult rats during gestation and lactation. The pups were killed at weaning. Synaptosomes, brain microvessees and retina were shown to contain the highest levels (about 0.5% of total fatty acids) of thetrans isomer of docosahexaenoic acid (22∶6 Δ4c, 7c, 10c, 13c, 16c, 19t). This compound was also observed in myelin and sciatic nerve, but to a lesser extent (0.1% of total fatty acids). However, the ratios of 22∶6trans to 22∶6cis were similar in all the tissues studied. When the diet was deficient in α-linolenic acid, the incorporation oftrans isomers was apparently doubled. However, comparison of the ratios oftrans 18∶3n−3 tocis 18∶3n−3 in the diet revealed that thecis n−3 fatty acids were more easily desaturated and elongated to 22∶6n−3 than the correspondingtrans n−3 fatty acids. An increase in 22∶5n−6 was thus observed, as has previously been described in n−3 fatty acid deficiency. These results encourage further studies to determine whether or not incorporations of suchtrans isomers into tissues may have physiological implications.

Lymphatic absorption of phytosterol oxides in rats.

Two of the main classes of oxyphytosterols (7-keto and epoxides) were synthesized from sitosterol and campesterol and given to mesenteric duct-cannulated adult male rats. Lymph was collected during 24 h and was analyzed for oxysterols. The results showed that the lymphatic recovery of the phytosterol oxides was low: 4.7% of the given dose for epoxy derivatives and 1.5% for 7-keto compounds. The campesterol oxides presented a better absorption than the sitosterol oxides. During the process of absorption’ the epoxyphytostanols were also partly transformed in campestanetriol and stigmastanetriol.

Formation of fatty acid geometrical isomers and of cyclic fatty acid monomers during the finish frying of frozen prefried potatoes

Abstract Frozen prefried French fries were deep fried in peanut and in soybean oils. Thirty frying operations were conducted at 180, 200 and 220 °C for 5 min. The quality of both the oil and the French fries was assessed by measuring the amount of polymers, polar components, fatty acid geometrical isomers and cyclic fatty acid monomers (CFAM). The structures of the CFAM were determined using gasliquid chromatography coupled with mass spectrometry (GC-MS).The results indicated that the starting oils contained some geometrical isomers of linoleic acid (0.9% in soybean and 1.6% in peanut of the total 18:2). Soybean oil also contained the monotrans isomers of linolenic acid (9.2% of the total 18:3). The amounts of 18:2 Δ9c,12t and 18:2 Δ9t,12c only increased after 10 frying treatments at 220 °C while no differences were observed at 180 and 200 °C. Similarly, no differences were found for the 18:3 geometrical isomers content at 180 and 200°C, while these increased at 220 °C. Furthermore, ditrans 18:3 isomers were formed above 200 °C. The amount of CFAM increased when increasing the temperature and the number of frying operations. No major differences in the quantity of CFAM were observed for products fried in peanut or soybean oils. However, the relative proportions of CFAM were different for a product fried in an oil containing an appreciable quantity of linolenic acid (soybean oil) compared with the french fries fried in peanut oil. The CFAM were distributed in both the nonpolar and the polar fractions.

Occurrence of N-3 trans polyunsaturated fatty acids in human platelets

Abstract Human platelets fatty acid profiles were studied with particular interest to isomers of eicosapentaenoic and docosahexaenoic acids. C20:5 Δ 17 trans isomer was detected in most of the samples (up to 0.48% of total fatty acids). Some samples also contained the Δ 19 trans isomer of docosahexaenoic acid (0.05% max.).

Heat treatment of vegetable oils III. GC-MS characterization of cyclic fatty acid monomers in heated sunflower and linseed oils after total hydrogenation

Fractions of cyclic fatty acid monomers (CFAM) were isolated from linseed oil heated at 275°C for 12 hr under nitrogen, at 240°C for 10 hr under nitrogen and at 240°C for 10 hr under air. Cyclic fatty acid monomers fractions were also isolated from a sunflower oil heated at 275°C for 12 hr under nitrogen and at 200°C for 48 hr in a commercial fryer. The CFAM fractions were hydrogenated and their composition studied by gas liquid chromatography coupled with mass spectrometry (GC-MS). The CFAM in the fraction isolated from heated linseed oil samples were a mixture (1:1) ofcis andtrans cyclopentyl and cyclohexyl isomers, while the CFAM in the fractions isolated from heated sunflower oils were mostly cyclopentyl isomers. The major cyclopentyl isomers weretrans andcis methyl 7-(2′-hexylcyclopentyl) -heptanoate, methyl 9-(2′-butyl-cyclopentyl)-nonanoate and methyl 10-(2′-propylcyclo-pentyl)-decanoate. The major cyclohexyl isomers were thetrans andcis methyl 9-(2′-propylcyclohexyl)-nonanoate which represented about 50% of the CFAM isomers isolated from heated linseed oil samples.