J.L. Le Quéré

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. 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.

Dynamic headspace analysis of Emmental aqueous phase as a method to quantify changes in volatile flavour compounds during ripening

Abstract The headspace compounds of Emmental aqueous phase (juice) and oil were analysed during ripening by dynamic headspace-gas-chromatography–mass spectrometry. We first checked that peak areas varied linearly with concentrations by using a standard addition method for 9 compounds. The slopes of linear regression curves were 1–1800 times higher for juice than for oil, indicating that these compounds were more easily released from juice. Consequently, although most flavour compounds are more concentrated in cheese oil than in cheese juice, they were similarly recovered from the headspace of both types of samples. Eighty-two compounds were identified, 70% of them being found in both juice and oil. Alcohols and esters markedly increased in number and concentration, essentially during the ripening in the warm room, as well as, to a lesser extend, sulphur compounds, methyl ketones, and 3-methylbutanal, whereas the other aldehydes decreased.

Flavonoid constituents of Stachys aegyptiaca

Abstract Twenty-four flavonoids were isolated from Stachys aegyptiaca Pers. Twelve glycosides were identified as vicenin-2, lueenin-2, apigenin and luteolin 7-glucosides and 7-diglucosides, chrysoeriol 7-glucoside, isoscutellarein 7-allosyl(1→2)glucoside, isoscutellarein 7-[6‴-acetylallosyl-(1→2)glucoside, hypolaetin 7-[6‴-acetylallosyl-(1→2)-3″-acetylglucoside] (newly reported), apigenin 7-[6‴-acetylallosyl(1→2) glucoside] and luteolin 7-[6‴-acetylallosyl-(1→2)glucoside]. Twelve aglycones were also isolated and identifed as apigenin, luteolin, chrysoeriol, xanthomicrol, sideritiflavone(?), 5,4′-dihydroxy-6,7,8,3′-tetramethoxyflavone, 5-hydroxy-6,7,8,3′,4′-pentamethoxyflavone, calycopterin, chrysosplenetin, 5-hydroxy-3,6,7,8,4′-pentamethoxyflavone, 5,3′,4′-trihydroxy-3,6,7,8-tetramethoxyflavone and 5,4′-dihydroxy-3,6,7,8,3′-pentamethoxyflavone.

Inactivation of lactococcal aromatic aminotransferase prevents the formation of floral aroma compounds from aromatic amino acids in semi-hard cheese

The enzymatic conversion of aromatic amino acids to aroma compounds plays a role in the formation of an undesirable floral aroma in Cheddar-like cheeses. In lactococci, the first step of aromatic amino acid degradation is a transamination, catalysed by an aromatic aminotransferase (AraT). We observed previously that in vitro, araT inactivation prevented degradation of aromatic amino acids and decreased degradation of Met and Leu. In this study we evaluated the effect of araT inactivation in Lactococcus lactis on flavour development in St. Paulin-type cheese. The degradation of amino acids was monitored by using radiolabelled amino acids and the volatile compounds formed were analysed by GC-MS. The development of cheese odour was also evaluated by sniffing. We confirmed that the availability of an α-ketoacid acceptor for transamination is the first limiting factor for amino acid conversion to aroma compounds in cheese. In the presence of α-ketoglutarate, araT inactivation greatly prevented formation of floral aroma compounds from aromatic amino acids while it did not affect the formation of volatile aroma compounds from branched-chain amino acids and methionine. However, the sensory analysis by sniffing did not reveal any significant effect of the gene inactivation although the odour of cheese made with the mutant tended to be less floral than that of cheese made with the wild type strain.

Production of 6-pentyl-α-pyrone by Trichoderma sp. from vegetable oils

Abstract A total of 108 strains of Trichoderma sp. were compared for their ability to produce 6-pentyl-α-pyrone (6PP), a coconut-like aroma. Among them, one strain, Trichoderma viride TSP2, demonstrated a good ability to produce 6PP from several commercial vegetable oils including castor oil (C18:1, OH n-7=89.3%), hazelnut oil (C18:1=78.6%), grapeseed oil (C18:2=66%) and linseed oil (α-C18:3=46.6%). By increasing the oil concentration from 5 to 20%, 1.2 g l−1 of 6PP was achieved after 6 days of cultivation. In comparison, 80 mg l−1 of 6PP were produced when glucose (30 g l−1) was used as the carbon source.

Production of halogenated compounds by Bjerkandera adusta.

The white-rot fungusBjerkandera adusta produces volatile chlorinated phenyl compounds. The main compounds identified were 3-chloro-4-methoxybenzaldehyde (3-chloro-p-anisaldehyde), 3-chloro-4-methoxybenzyl alcohol (3-chloro-p-anisyl alcohol), 3,5-dichloro-4-methoxybenzaldehyde (3,5-dichloro-p-anisaldehyde), and 3,5-dichloro, 4-methoxybenzyl alcohol (3,5-dichloro-p-anisyl alcohol).p-Anisaldehyde, veratraldehyde and the corresponding alcohols,p-anisyl alcohol and veratryl alcohol were produced simultaneously. Even with a very low concentration of chloride in the medium (< 10−5m), chlorinated aromatic compounds were still observed. Addition of bromide to the culture medium led to the production of brominated compounds: 3-bromo-4-methoxybenzaldehyde, 3-bromo-4-methoxybenzyl alcohol, 3,5-dibromo-4-methoxybenzaldehyde and 3-bromo-5-chloro-4-methoxybenzaldehyde. These brominated compounds have not previously been reported as natural products. Although iodo-aromatic compounds were not produced by supplementation of the medium with iodide, isovanillin was found in the culture broth under these conditions. This compound may be formed by substitution of the iodine intermediate by a hydroxyl group on the third carbon of the ring. Diiodomethane or chloroiodomethane were also found. It is the first time that the production of halomethane has been related to the production of halogenated aromatic compounds. All the strains tested have these capabilities.

CHEMISTRY OF DEFENSIVE SECRETIONS IN NYMPHS AND ADULTS OF FIRE BUG, Pyrrhocoris apterus L. (HETEROPTERA, PYRRHOCORIDAE)

The defensive secretions from the nymphs and the adults of both sexes inP. apterus were chemically investigated. Forty components were identified from the nymphal posterior dorsoabdominal glands and 35 from the adult metathoracic glands of both sexes. Within the 43 identified chemicals, we found 23 aldehydes, five saturated hydrocarbons, five alcohols, three ketones, three lactones, two terpenes, one phenol and one ester. Thirteen of these compounds had never been reported within the Heteroptera. Whereas eight components are specific to the nymphs, methyl pentenal, (E)-2-hexenol, and heptadecanal are the only adult-specific components. The biological role of all the identified chemicals is almost unknown inP. apterus and is discussed comparatively with regard to other Heteroptera.

IDENTIFICATION OF AN OVIPOSITION-DETERRING PHEROMONE IN THE EGGS OF THE EUROPEAN CORN BORER

The European corn borer (ECB) Ostrinia nubilalis (Lepidoptera, Pyralidae), a serious pest of corn is a polyphagous insect which can damage various crops such as cot ton and vegetables [1, 2]. In the United States, the average yield reduction caused by this insect in susceptible corn hybrids in 1986 was 40 % [3]. Females lay masses of 2 0 4 0 eggs mainly on the lower surfaces of the leaves. In this species, the egg masses are often observed at low density levels in the field [4] and the spatial distribution of the egg masses suggests a possible intraspecific regulation of the oviposit ion behavior. We assumed that the egg-laying behavior of this species could be chemically mediated by pheromones present on the egg masses. Oviposit ion-deterring pheromones (ODP) produced by eggs have been observed both in species which lay isolated eggs [5] and which aggregate eggs [6]. ODP can be produced by different sources. Larval frass extracts have been shown to be oviposit ion deterrents in species like Spodoptera littoralis [7] or Ostrinia nubilalis [8]. In most of the investigated species, the chemical nature of the ODP remains unknown. We report the first evidence of the deterrent effect of egg extracts on the oviposit ion behavior of the ECB, and the identification of active components as methyl esters of simple aliphatic acids. We also observed a chemically mediated regulation of the egg mass size. This pheromone may help to explain the distribution of ECB egg masses on plants and represent a possible mode of chemical control of this pest. The insects studied came from an INRA strain (Le Magneraud, France) annually infused with insects collected

On-line hydrogenation in GC-MS analysis of cyclic fatty acid monomers isolated from heated linseed oil

A simple on-line hydrogenation method in GC-MS analysis of unsaturated fatty acid esters is described. Using hydrogen as carrier gas, hydrogenation takes place in a capillary reactor connected to the outlet of the analytical column in the oven of the gas chromatograph. The reactor is a fused silica tube (60 cm×0.32 mm i.d.) coated with palladium acetylacetonate. Selective hydrogenation of olefinic bonds is achieved after a normal chromatographic run. Structural information (carbon-skeleton, double bond equivalents) can thus be deduced, and structural correlations between the saturated and unsaturated components can be obtained. Structures of cyclic fatty acid esters isolated from heated linseed oil were elucidated using this simple method which was found very useful for structural investigations on unsaturated compounds by GC-MS.