Ketonic rancidity is associated with the lauric acid oils and butterfat. It arises when short and intermediate carbon chain length fatty acids (C6 to C14) are converted into methyl ketones (C5 to C13) by certain fungi. Ketonicrancidity will not occur in fats and oils that do not contain these fatty acids. Fermentation experiments with whole oils and simple triglycerides confirmed that only short and intermediate carbon chain length fatty acids were converted into methyl ketones. Methyl ketones produced contained one carbon atom less than the parent fatty acid. Tetradecanoic acid was the longest fatty acid to undergo conversion into its corresponding methyl ketone. Experiments with free fatty acids established that short and intermediate carbon chain length fatty acids inhibited the growth of Penicillium crustosum, Evidence was presented to demonstrate that the mitochondrion was a site of antifungal activity. It was concluded that the conversion of fatty acids into methyl ketones was a detoxification mechanism for their removal from the environment. Extrinsic factors (temperature, pH, aw, preservatives and O2 removal) were used to control fungal growth and ketonic rancidity. Fungal homeostatic mechanisms often enabled P.crustosum to grow under unfavourable environmental conditions. It was suggested that acombination of preservation measures should be used to prevent ketonic rancidity in the lauric acid oils and their products.

Fish provides a major source of proteins and polyunsaturated fatty acids which are known to prevent coronary heart diseases. However, inherent characteristics such as colour and texture prevent the effective utilisation of some fish, especially fatty pelagics for human consumption. Instead, they are used for fish oil and fish meal production. For this reason and for enhancing the utilisation of valuable resources, the physico-chemical properties, which may be species specific, were investigated in relation to two Namibian species, namely, horse mackerel (Trachurus capensis) and snoek (Thyrsites atun). The results showed that horse mackerel (Trachurus capensis) and snoek (Thyrsites atun) contain high contents of palmitic acids (29%), oleic acids (25%), and the omega-3-polyunsaturated fatty acids, such as docosahexaenoic acids (DHA) (15%) and eicosapentaenoic acids (EPA) (9%). The studies also showed that optimum protein extractability was obtained with 5% NaCl at pH 7.2 and the highest gel strength at pH 6.5-7.0. CaCO3 had detrimental effect on the water-holding capacity when used above 50mg.l-1 in washing water. Agar and sodium alginate extracted from Namibian Gracilaria verrucosa (red seaweed) and Laminaria schinzii (brown seaweed) respectively, were also characterised for their physico-chemical properties. Both the nontreated and treated agars were observed by colorimetric method to contain low levels of sulphate, an observation also confirmed by NMR and Raman FTIR spectroscopy. Sodium alginate was found to contain high content of guluronic acid (75%) by NMR, a good index of strong gelling ability. The good functionalities obtained as a result of optimising the physicochemical properties of fish proteins and seaweed polysaccharides enabled an investigation of the interactions of the two components. Studies on the interactions of the both horse mackerel and snoek with either sodium alginate or agar were undertaken by rheology, differential scanning calorimetry and phase contrast microscopy. Large deformation and small deformation rheological studies showed a decrease in the gel strength of fish proteins with the addition of either polysaccharide at all combinations. The DSC results indicated a lowering of the denaturation temperature with the addition ratios of increasing amounts of sodium alginate to fish proteins. Although the mixture of fish proteins and agar resulted in the lowering of the denaturation temperature, the shift; was not as pronounced as that obtained with sodium alginate. The reason for the lowering of gel strength and G' values was attributed to phase separation of fish proteins and polysaccharides which was reflected by phase contrast microscopy studies. This investigation has resulted in the characterisation of valuable fish and seaweed polysaccharide resources from Namibia which could be used in combination for the development of new food products.

Part I. Synthetic studies. cis-Hydroxylation of Long-chain Olefins. The Woodward cis-hydroxylation procedure, involving the use of iodine and silver acetate in wet acetic acid, has been adapted and applied to the cis-hydroxylation of long-chain olefins. It is a satisfactory method for oxidising these compounds and has some advantages over other methods of cis-hydroxylation. A further cis-hydroxylation procedure, Involving the use of iodine and silver nitrate in acetonitrile has also been developed. Part II. Degradative Studies. The EPOXY Acid in Cameline Oil. A hydroxy acid, isolated from Camelina sativa seed oil, has been shown to be threo-15:16-dihydroxyoctadec-cis-9cis-12-dienolc acid. Infra-red studies indicate that this acid, is present in the oil as glycerides of cis-l5:16-epoxylinolele acid and Is thus closely related to the only other naturally occurring long-chain epoxy acid viz. cis-12:13-epoxyolelc acid. Part III. Analytical Studies. The Occurrence of 9-hydroxy-octadec-cis-12-enoic Acid in Various Strophanthns Oils. 9-Hydroxyoctadec-12-enoic acid has been identified, qualitatively and quantitatively, in ten Strophanthus oils. In two oils a small amount of optically active erythro-9:10-dihydroxystearic acid accompanies the monohydroxy acid and may occur throughout the genus. The oils have been analysed by throe methods and these are discussed comparatively. The analytical results lead to some generalisations and correlations. Part IV. Configurational Studies. 9-Hydroxyoetadec-cis-12-enoic acid has been isolated and three of the four isomeric 9:12:13-trihydroxystearic acids prepared from it. The rotations of these and other hydroxy acids have been measured. It is tentatively suggested that the 9-hydroxy acid has the D-configuration, thus being in the same series as natural riclnoleic acid. Unsuccessful attempts to synthesise long-chain dihydroxy acids, of known configuration, by extension of the chain of optically active tartaric acid are reported and a more suitable synthetic route is suggested. Part I. Synthetic studies. cis-Hydroxylation of Long-chain Olefins. The Woodward cis-hydroxylation procedure, involving the use of iodine and silver acetate in wet acetic acid, has been adapted and applied to the cis-hydroxylation of long-chain olefins. It is a satisfactory method for oxidising these compounds and has some advantages over other methods of cis-hydroxylation. A further cis-hydroxylation procedure, Involving the use of iodine and silver nitrate in acetonitrile has also been developed. Part II. Degradative Studies. The EPOXY Acid in Cameline Oil. A hydroxy acid, isolated from Camelina sativa seed oil, has been shown to be threo-15:16-dihydroxyoctadec-cis-9cis-12-dienolc acid. Infra-red studies indicate that this acid, is present in the oil as glycerides of cis-l5:16-epoxylinolele acid and Is thus closely related to the only other naturally occurring long-chain epoxy acid viz. cis-12:13-epoxyolelc acid. Part III. Analytical Studies. The Occurrence of 9-hydroxy-octadec-cis-12-enoic Acid in Various Strophanthns Oils. 9-Hydroxyoctadec-12-enoic acid has been identified, qualitatively and quantitatively, in ten Strophanthus oils. In two oils a small amount of optically active erythro-9:10-dihydroxystearic acid accompanies the monohydroxy acid and may occur throughout the genus. The oils have been analysed by throe methods and these are discussed comparatively. The analytical results lead to some generalisations and correlations. Part IV. Configurational Studies. 9-Hydroxyoetadec-cis-12-enoic acid has been isolated and three of the four isomeric 9:12:13-trihydroxystearic acids prepared from it. The rotations of these and other hydroxy acids have been measured. It is tentatively suggested that the 9-hydroxy acid has the D-configuration, thus being in the same series as natural riclnoleic acid. Unsuccessful attempts to synthesise long-chain dihydroxy acids, of known configuration, by extension of the chain of optically active tartaric acid are reported and a more suitable synthetic route is suggested.

The commercial hydrogenation of oils and fats results in the formation of, among other components, geometrical and positional isomers of monounsaturated fatty acids. The view that there may be hazards associated with such oils have occasionally been expressed. Prior to an investigation of the levels of such acids in human tissue and UK dietary fats, the synthesis of a series of these acids, as standards, and their characterisation, was necessary. For the synthetic programme, the general scheme provided a convenient route for the synthesis of geometrical and positional isomers from common precursors. When condensation of the 1-alkyne and a-chloro-w-iodoalkane was performed via sodamide in liquid ammonia, the scheme was limited but was extended somewhat when performed via methyllithium in dioxan. Generally, yields decreased with the increasing chain length, and migration of the unsaturated bond to the extremities of the resulting molecule. Chromatographic separation, both capillary column GLC and reversephase HPLC, was readily achieved on the basis of chain length and configuration of the double bond. Furthermore, the partial separation of positional isomers was achieved. NMR spectroscopy unambiguously determined the configuration and position of unsaturation in virtually every fatty acid. Assignment is based on the fact that functional groups within an acid alter the chemical shift of neighbouring carbons in a characteristic manner. No one of these techniques alone is applicable to the determination of positional isomerism in a complex lipid mixture and must be used in combination. Whereas NMR is undoubtedly invaluable in the quantification of positional isomers on an individual basis, or in profiling simple mixtures, it is not as applicable to the direct analysis of complex lipid samples. Emphasis on the continuing development of capillary column GLC holds the most promise for the direct quantification of positional isomerism.

No description available.

A wide range of [1-14C] monoenoic (32) and polyenoic (8) fatty acids and two unlabelled fatty acids containing a 6,7-cyclopropene ring were prepared by existing methods. Several procedures for the conversion of oleic acid to its C17 iodide with concomitant decarboxylation were investigated without success. The CMR spectra of (27) saturated, (65) cis and trans monoenoic, (39) monoynoic, (2) cyclopropene, (20) cis-polyenoic, (14) diynoic and (10) mixed-function diunsaturated acids and methyl esters were recorded and interpreted. An empirical approach, based on the shielding and deshielding influence of functional groups on the rest of the molecule, was employed, and the assignment of 13C resonances by this method agreed with those obtained by other researchers using different methods. The shielding and deshielding effects were generally additive, except when two function groups were close together. CMR spectroscopy can be used to distinguish cis and trans olefins, locate double and triple bond positions and interpret patterns of polyunsaturation. The specificity of the mammalian desaturases was examined by incubating [1-14C] fatty acids with a rat liver microsomal preparation and analysing the products formed after one hour. The Delta9 desaturase was believed to hold its substrate by the binding of the CoA moiety at the carboxyl end and by the fit of the alkyl chain into a deep, narrow cleft, where, except at the active centre, it was constrained to take up predominantly trans conformations. This model is confirmed. Trans monoenoic acids were generally Delta9 desaturated to give as high conversions as saturated acids, and the Delta7t and Delta11t monoenoic acids gave the corresponding Delta7t9c and Delta9c11t conjugated dienes. Cis monoenoic acids, which were not expected to fit into the enzyme cleft between C(5) and C(15), were not Delta9 desaturated unless the double bond position was beyond Delta13, and even then they were much poorer substrates than stearic acid. The Delta6 desaturase shows a much wider substrate specificity than was previously anticipated. The enzyme can accommodate a wide range of substrate chain lengths (at least C14 to C22) and the Delta9 cis double bond is not obligatory for Delta6 desaturation. The model advanced for the enzyme contains two distinct features. Firstly, a region of steric constraint between C(10) and C(13) on the substrate geometry acceptable to the enzyme is proposed. Secondly, pi-bond binding sites on the enzyme surface in the C(9) to C(13) region are envisaged. Dienoic acids with a Delta9c double bond and adjacent olefinic unsaturation (Delta11- Delta13) were much better substrates than monoenoic acids or dienoic acids containing a Delta9c double bond and a second double bond beyond the Delta13 position. Therefore, to bed substrate for Delta6 desaturation the co-operative binding of two ands, separated by 0-2 methylene groups, to these Delta-binding is essential. The Delta5 desaturase also shows a wider substrate specificity than was previously anticipated. The principal feature is a high degree of chain length specificity. Within the C16-C20 range tested C20 was the optimum chain length while minimal Delta5 desaturation occurred when the chain length dropped to C16. A region of steric constraint between C(10) and C(13) on the substrate geometry acceptable to the enzyme is envisaged. However, the range of acids tested was not extensive and an evaluation of the role of Delta-bonds in substrate-enzyme binding was not possible. No Delta4 des1aturation was observed. This agreed with other studies.

Ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline (I)), ethoxyquin nitroxide (II), 2,6-dihydro-2,2,4-trimetbyl-6-quinolone (III) and l,2-dihydro-6-hydroxy-2,2,4-trimethylquinoline (IV) were prepared and purified in order to study their antioxidant properties in fish meal and/or oil. I (also commercally available) and III were equally effective in fish meal, but III and IV were better in oil than I and II. In AIBN initiated methyl linoleate autoxidation, the order of efficiency in terms of the stoichiometric factor (n), using BHT as a standard, was IV > I > BHT > II. On the other hand, III gave very little inhibition in this system. In fish meal and oil, I was converted to III and to a 1,8'-dimer (V). The same products were formed in tert-butoxy oxidation of I. The nitroxide (II) was also formed from I but this was only seen by ESR in various organic solvents. It is likely to play some role in the antioxidant mechanism of I. The 1,8'-dimer was isolated and found to have no antioxidant properties in oil. Another reaction product of 1,2,4-dimethyl-6-ethoxyquinoline was also prepared. It was found to show prooxidant effects in fish oil.

An attempt has been made to compare anodic synthesis, malonation, and chain-extension with enamines as procedures for converting readily-available acids to higher homologues. Anodic synthesis was successfully employed to prepare esters of several olefinic acids (20:1 11c, 22:1 13c, 20:2 11c 14c, 22:2 13c 16c, 20:3 8c 11c 14c), acetylenic acids (18:1 16a, 18:1 17a), and saturated acids of 'odd' chain length (13:0, 15:0, 17:0, 19:0, 21:0). The desired esters were recovered from the reaction products by column chromatography and further purified when necessary by crystallisation. Yields were usually in the range 40-50%. Some difficulty was encountered with acids having △5 and △6 unsaturation and this made the chain-extension of γ-linolenic acid by this procedure unsatisfactory. A possible reason for this is discussed. An electrolytic procedure for converting long-chain acids (RCO H) to their nor-alcohols (ROH) has been examined: oleic, linoleic, and ricinoleic acid were converted to the corresponding C17 alcohols. Oleic, linoleic, ɑ-linolenic and γ -linolenic acids were successfully converted to their C20 homologues in 70-80% yield by an improved malonation procedure which was recently described. In one case the malonation was repeated to give a C22 acid. The enamine chain-extension procedure was briefly examined using cyclopentanone and cyclohexanone to furnish heneicosanoic and eicbsanoic acids respectively The 13C NMR spectra of the starting materials and products have been recorded. It has proved possible to allocate the observed resonances (with greater or lesser certainty) to all the constituent carbon atoms and some interesting generalisations are presented. A minor study was concerned with the preparation of long-chain hydroperoxides and peroxides by reaction of the mesylates of some primary alcohols (stearyl, oleyl, linoleyl) with hydrogen peroxide and t-butyl peroxides. Some secondary peroxides were formed by a similar reaction with allylic bromides.

Part I. The preparation and reactions of long-chain acids containing sulphur. Much is known about long-chain hydroxy esters and the epoxides which can be derived from them but information about the corresponding sulphur compounds is sparse. Using various methods, methyl 12-mercaptostearate, methyl 9-mercaptostearate, methyl 12-mercapto-oleate, methyl 12-mercapto-elaidate, methyl 9(10)-mercaptostearate, methyl 12"hydroxy-9(10)-mercaptostearate, methyl 9-hydroxy-12(13)-mercaptostearate and 1-mercapto-octadec-4- and 5-ene have been prepared. In reaction with sodium hydrogen sulphide without the rigorous exclusion of air the major product produced from methyl 9-mesyloxy- octadec-cis-12-enoate was methyl 9,12-epithiostearate. A similar result was observed with another γ-mercapto alkene (1-mercapto-octadec-4-ene) and with a 8-mercapto alkene (l-mercapto-octadec-5-ene), but not with a hydroxy alkene (methyl ricinoleate). For confirmation of these conclusions methyl 9,12-epithiostearate was synthesised by an independent and unambiguous route. By an extension of the procedures applied for monomercapto esters, 1,2-dithiols (methyl erythro- and threo-9,10-dlmercapto- stearate), a 1,3-dithiol (methyl 10,12-dimercaptostearate), and a 1,4-dithiol (methyl 9,12-dimercaptostearate) have been prepared from the corresponding dihydroxy compounds. The 1,3- and 1,4-dithiols are readily converted to cyclic epidisulphides by oxidation. The infrared, NMR and mass spectral properties of these compounds have been investigated. 1,2-Epithiostearates (methyl cis and trans-9,10-epistearate) have been prepared by two different routes and their chromatographic (TLC, GLC) and spectroscopic (NMR, MS) behaviour studied. Part II: The synthesis of some C₁₆ and C ₁₈-acids of geneal formula CH₃ (CH₂)[sub]m(CH=CH)[sub]n CO₂H. Commercially available trienoic (△ 2, 4, 6) and tetraenoic acids (△2, 4, 6, 8) of medium chain length have been used successfully in the study of acyl-CoA synthetases of medium chain length specificity. But their activity with long chain acyl-CoA synthetases is rather low. The synthesis of C ₁₆ and C ₁₈ trienoic and tetraenoic acids has therefore been examined. The triene esters were successfully prepared by the reaction of appropriate aldehydes with phosphonates prepared from methyl 6-bromo-hexa-2,4-dienoate and the tetraene esters by interaction of 2,4-dienals with a phosphorane. The C₁₂, C₁₄ and C₁₆ dienals were prepared from l-methoxybut-1-en-3-yne by condensation with the appropriate saturated aldehyde. The chromatographic (GLC) and spectroscopic (UV, IR, NMR, and MS) properties of these acids have been examined and some simple thiol esters made. Their biochemical use as reagents for the estimation of long-chain Co-A synthetases is being conducted elsewhere.

No description available.