Methyl linolenate, products from

As a reasonable biogenetie pathway for the enzymatic conversion of the polyunsaturated fatty acid 3 into the bicyclic peroxide 4, the free radical mechanism in Equation 3 was postulated 9). That such a free radical process is a viable mechanism has been indicated by model studies in which prostaglandin-like products were obtained from the autoxidation of methyl linolenate 10> and from the treatment of unsaturated lipid hydroperoxides with free radical initiators U). 

Methyl Tricarboxyoctadecanoate, 3. The product from Run 12, Table I, was characterized functionally by comparing GLC, TLC, and mass spectra of corresponding derivatives from hydroformylated methyl linolenate (21). Mass spectrum m/e (fragment, relative intensity) 472... 

LOO additions increase with heat (289), extent of oxidation (290), and solvent polarity (266). Dimer levels of methyl linolenate autoxidized neat at room temperature varied from 0.1% to 10.1%, proportional to peroxide values (290). MLn autoxidized at 40°C to PV 1062 gave 6.8% dimers 80% of these were from LOO and 20% were from epidioxide-OO additions. The dimer linkages were mostly C—O—O—C at lower temperatures, but shifted to C—C and C—O—C as the temperature increased (276). At PV = 4002, LOO additions increased to 55% of the products. Epidioxide peroxyl radicals, in particular, showed a very strong tendency to add to double bonds, with greater than 90% dimerization at 40°C. 

Polyunsaturated eompounds, such as methyl linoleate (13) and methyl linolenate (14) offer some interesting possibilities. There are three main sets of products (hydrocarbons, monoesters and diesters), identified by mass spectroscopy (MS) and listed in Table 7.3 (Ast 1976a Verkuijlen 1974, 1976). Cyclohexa-1,4-diene and traees of higher cyclopolyenes are formed. These must clearly result from secondary intramolecular metathesis reactions such as (6). 

Fig.l. Gas chromatograms (GC) of the methyl ester products converted from a-linolenic acid by Clavibacter sp. ALA2. (A) Bioconversion of a-linolenic acid by Clavibacter sp. ALA2. Peak I the product with GC retention time (Rt) of 18 min Peak II the product with GC Rt of 26 min. (B) Incubation of a-linolenic acid with autoclaved C/av/bacfer sp. ALA2. 

Neff, W.E., Frankel, E.N. and Weisleder, D. High-pressure liquid chromatography of autoxidized lipids II. Hydroperoxy-cyclic peroxides and other secondary products from methyl linolenate. Lipids 16, 439-448 (1981). 

Figure 4.16. Cleavage products from 9-, 12-, 13- and 16-hydroperoxides formed by autoxidation of methyl linolenate (Frankel et aL, 1981). Relative percent values shown in parentheses are for autoxidation and photosensitized oxidation respectively.

Volatile decomposition products from autoxidized methyl linolenate were characterized for their intense aroma impact by capillary gas chromatography-olfactometry. The most intense volatiles included raf2.s,c/5-2,6-nonadienal, l-c/5-5-octadien-3-one, trans,cis-3,S-octadicn-l-onQ and c/5-3-hexenal (Table 4.4). The mechanism suggested for the formation of l-c/5-5-octadien-3-one assumes as precursor the 10-hydroperoxide formed by singlet oxidation that... 

Figure 4.22. Volatile decomposition products expected from peroxide-linked dimers of methyl linolenate (Frankel etal, 1988).

The hydroperoxy epidioxides formed from photosensitized oxidized methyl linoleate are important precursors of volatile compounds, which are similar to those formed from the corresponding monohydroperoxides. Thus, 13-hydroperoxy-10,12-epidioxy-tra 5 -8-enoic acid produces hexanal and methyl lO-oxo-8-decenoate as major volatiles (Figure 4.24). The 9-hydroperoxy-10,12-epidioxy-rrans-13-enoic acid produces 2-heptenal and methyl 9-oxononanoate. Other minor volatile products include two volatiles common to those formed from the monohydroperoxides, pentane and methyl octanoate, and two that are unique, 2-heptanone and 3-octene-2-one. The hydroperoxy epidioxides formed from autoxidized methyl linolenate produce the volatiles expected from the cleavage reactions of linolenate hydroperoxides, and significant amounts of the unique compound 3,5-octadiene-2-one. This vinyl ketone has a low threshold value or minimum detectable level, and may contribute to the flavor impact of fats containing oxidized linolenate (Chapter 5). 

As observed with the monohydroperoxides (Section D), thermal decomposition of the hydroperoxy bicyclo-endoperoxides from methyl linolenate produced more complex mixtures of volatile compounds than acid decomposition with acidic methanol. The thermal decomposition products included methyl 9-oxononanoate, propanal, 2,4-heptadienal, methyl octanoate, methyl 13-0X0-9,11-tridecadienoate and ethane (Figure 4.25X The acid decomposition products, analysed as the di- and tetramethyl acetals, comprised only propanal, methyl 9-oxononaoate, and malonaldehyde. As with the monohydroperoxides, by thermal decomposition the bicyclo-endoperoxides are cleaved on either side of the hydroperoxide group, whereas by acid decomposition they are cleaved only between the hydroperoxide group and the... 

The synergism exhibited by the ternary mixture of a-tocopherol, ascorbic acid and phospholipids has been shown to be due to the stabilization of a-tocopherol, on the basis of ESR studies with methyl linolenate oxidized at 90°C to detect the free radicals of a-tocopherol and ascorbic acid. Evidence was obtained by this technique for the formation of nitroxide radicals (R-N-0 ) in the presence of phosphatidylserine or phosphatidylethanolamine or soybean lecithin and oxidized methyl linolenate. However, as pointed out earlier (Section C), the synergistic activity of this ternary mixture may be derived from antioxidant products formed from the phospholipids at elevated temperatures by the Maillard browning reaction (Chapter 11). 

By the effect of a Rh/C catalyst modified with PPhg at 140 bar syngas pressure and 110 °C on a complex substrate mixture of fatty acid methyl esters with one or more double bonds, besides the formation of monoformyl stearate, some diformy-lated products were found [34]. Moreover, unsaturated monoformyl esters were detected together with triformyl esters derived from methyl linolenate. The formation of 1,4-diformyl esters in the hydroformylation of methyl linoleate over the 1,3-diformyl isomers was explained by the thermodynamic stability of the transient Rh-acyl complex A over the chelate B with a smaller ring size. 

Preparation and storage of products from both oilseeds is often inhibited by rancidity and bitter aroma defects caused mostly by volatile aroma active carbonyl compounds, e. g., (Z)-3-hexenal, (Z)-l,5-octadien-3-one and 3-methyl-2,4-nonan-dione. The rancidity-causing compounds are formed through peroxidation of linolenic acid, accelerated by the enzyme lipoxygenase and/or by hem(in) proteins (cf. 3.T.2.2). Furan fatty acids are the precursors in the case of the dione (cf. 14.3.2.2.5). Lipid peroxidation is also involved in the formation of another very potent odorant, 2-pentylpyridine, which produces grassy aroma defects in soybean products. Defatted soybean protein isolates contained 60-510 pg/kg of this compound, which with an odor threshold... 

A mixture of palladium chloride and triphenylphosphine effectively catalyzes carboxylation of linoleic and linolenic acids and their methyl esters with water at 110°-140°C and carbon monoxide at 4000 psig. The main products are 1,3-and 1,4-dicarboxy acids from dienes and tricarboxy acids from trienes. Other products include unsaturated monocar-boxy and dicarboxy acids, carbomethoxy esters, and substituted a,J3-unsaturated cyclic ketones. The mechanism postulated for dicarboxylation involves cyclic unsaturated acylr-PdCl-PhsP complexes. These intermediates control double bond isomerization and the position of the second carboxyl group. This mechanism is consistent with our finding of double bond isomerization in polyenes and not in monoenes. A 1,3-hydrogen shift process for double bond isomerization in polyenes is also consistent with the data. 

Fig. 1.13. Separation of a product of partial transesterificaiion of rapeseed oil with methanol using combined RPC and NARPC gradient elution. Column Separon SGX Cm, 7 pm, 150 x 3 mm i.d. Ternary gradient from 30% A + 70% B to 100% B in lO min and to 50% B -t- 507r C in 20 min. followed by isocratic elution with the final mobile phase composition for 5 min, at I ml/min. Injection volume 10 pi. UV detection at 205 nm. Notation of sample compounds Ln. L, O and G are used for linolenic acid, linoleic acid, oleic acid, gadoleic acid, respectively, and for their acid parts in mono-, di- aixl tri-acylglycerols and methyl esters Me means methyl in methyl esters.

Fatty acid epoxides have numerous uses. In particular, oils and fats of vegetable and animal origin represent the greatest proportion of current consumption of renewable raw materials in the chemical industry, providing applications that cannot be met by petrochemicals [64]. Polyether polyols produced from methyl oleate by the Prileshajev epoxidation (using peracetic acid) are an example. Epoxidized soybean oil (ESBO) is a mixture of the glycerol esters of epoxidized linoleic, linolenic, and oleic acids. It is used as a plasticizer and stabilizer for poly (vinyl chloride) (PVC) [1] and as a stabilizer for PVC resins to improve flexibility, elasticity, and toughness [65]. The ESBO market is second to that of epoxy resins and its world wide production... 

Bioconversion of a-Linolenic Acid by Clavibacter sp. ALA2. Several new peaks were detected on the GC chromatogram of the methyl ester derivative of a crude lipid fraction extracted from the culture medium after 7 d of incubation. The retention time (Rt) of the major product was 18 min under the GC conditions described in Methods and... 

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