die dem Gleichgewicht entsprechende Konzentration, was sich p i t der vorgiingig ausgefiihrten Desorptionshemmung der Olsaure interpretieren 1 a t .Die Selektivitat und das Ausmal3 der geometrischen Isomerisierung kann, wenn auch nur in begrenztem Umfang, durch die Reaktionsbedingungen beeintluBt werden. Dabei steht der Wasserstoffdruck im Vordergrund. Durch Druckreduktion kann die Linolselektivitat noch etwas gesteigert werden. Durch einen niedrigen Wasserstoffdruck wird him gegen die Isomerenverteilung zugunsten der trans-isomeren Elaidinsaure beeintluBt, w h e n d unter hohem Wasserstoffdruck mehr Olsaure als Zwischenprodukt entsteht. Die phanomenologische Beschreibung der Fetthydrierung ist mit erweiterten Langmuir-Hinshehd-Ansatzen moglich. Unter der Annahme nicht eingestellter Adsorptions-/Desorptionsgleichgewichte an der Katalysatoroberflache lassen sich die gemessenen Konzentrationsverlaufe in Abhhgigkeit der Temperatur und des Wasserstoffdrucks simulieren. Das Isomerisierungsverhalten der 01-und Elaidinsaure kann mit unterschiedlichem Sorptionsverhalten plausibel erkl&t werden, da die Weiterreaktion zur Stearinsaure unabhhgig von der geometrischen Konfguration der Monoene gleich s h e l l ablauft. L i t e r a t u r WZchau, Fette . Seifen . Anstrichmittel 81,303 [ 19791. M. Mtiwing, Dissertation ETH Nr. 8066,1986. A. S e h , H. Pardun u. M . A r m , Fette ' Seifen . Anstrichmittel 80, 58 [ 19781. Landolt-Bomstein, 6. Auflage, II. Band, 4. Teil, Tabelle 241122/1, Springer-Verlag, 1961. G. Gut, Swiss Chem. 4/3a, 17 [ 19821. L. F Albnght, J. h e r . Oil Chemists' SOC. 40,16 [ 19631. G. Gut, J. Kosinka, A . Babuki u. A. Schuerch, Chem. Eng. Sci. 34, 1051 [ 19791.N o m e n k l a t u r Symbol Bedeutung Einheit C C H JZ k k* Ki L Ln mK P r S Q S I SU SI t T T @H Konzentration mol/L OIsaure (cis) Henrykonstante L bar/mol Jodzahl(= Anzahl GrammJod, die mit 100 g 0 1 unter Addition an Doppelbindungen reagieren) Reaktionsgeschwindigkeitskonstante mol/(L min %Kat) druckabhhgige Reaktionsgeschwindigkeitskonstante (= k e H ) mol/(L min %Kat) Sorptionsgleichgewichtskonstante Wmol Linolsaure Linolensaure Katalysatormenge Druck Sorptionsquotienten Reaktionsgeschwindigkeit Stearinsaure Linolenselektivitat holselektivitat Trien -kl-> Dien -k2-> Monoen -B-> gesiittigt Isomerisiemngsindex (= A%trans/AJZ) Reaktionszeit min Elaidinsaure (trans) Redeckungsgrad der Katalysatoroberflache mit Wasserstoff (= rL4-X") = [CL~CLnI max) (= rc+&(-d = [(CC+CT/CLlrnax) Temperatur OC GewO/n bar moV(L min) Eingegangen a m 14. Juli 1986.The seed chemical composition and oil physical and chemical constants of two imported rapeseed German varieties and one locally produced in Egypt were studied. Rapeseeds are chamcterized by high lipid and protein contents. The fatty acid analysis indicated that palmitic and oleic acids were the most prevalent saturated and unsaturated acids, respectively. Also, the rapeseed oils under study were free from long-chain fatty acids (>C,,). The unsaponifiables were fractionated by GLC into 36 different compounds of ...

No abstract

The present investigation into the effect of amino acids on linoleic acid oxidation in freeze‐dried model system illustrates the existence of an autocatalytic chain reaction, in which all amino acids, except cysteine, exhibited minor antioxidant behavior. The antioxidant effect might be attributed to the absence of protonated amino nitrogen. Linoleic acid alone had an induction period of 15 hr, and on the addition of various α‐amino acids, the systems had induction periods ranging from 16‐19 hr. This increase did not exhibit any specific function for the studied amino acids. Cysteine exhibited an exceptional prooxidant effect due to the role of the HS‐group. The addition of copper at concentrations of 10‐5M and 10‐3M to the model systems composed of linoleic acid and various a‐amino acids exhibited minor and highly prooxidant effects, respectively, The prooxidant effect of these amino acids in the presence of copper might be due to amino acids‐copper complexes.

Model systems were designed to study linoleic acid oxidation in the presence and absence of various amino acids with or without cupric ions. The tested amino acids exhibited a potential prooxidant effect in linoleic acid dispersed in aqueous media. The effectiveness of various amino acids on linoleic acid oxidation decreased in the following order: cysteine > serine > tryptophan > phenylalanine > histidine > alanine. The addition of alanine, serine, phenylalanine, histidine, or tryptophan to linoleic acid showed an autocatalytic chain reaction. With cysteine, there was a linear relation between concentration of hydroperoxides and time during the early stages of oxidation. The prooxidative activity of the tested amino acids in general could be attributed to the presence of the a‐amino group in the form H3‐N‐R. The apparent difference in the prooxidative activity is mainly due to the functional groups attached in the β‐carbon atom in the amino acid molecules. The addition of cupric ions at a concentration of 10‐5M to linoleic acid catalyzed with various a‐amino acids showed that these amino acids had no significant effect. Increasing the copper concentration from 10‐5M to 10‐3M had the following effects: a shortening of the induction period of linoleic acid catalyzed by amino acids having an aromatic side chain, no effect on the induction period but an increase in the oxidation rate during the propagation step in the model systems catalyzed by alanine and serine, and in the model system containing cysteine a linear increase in the linoleic acid oxidation from the start of the reaction.

a r a g , S. A . O s m a n , S. A . S. H a l l a b o and A . A . N a s r ' :Model systems were designed to study the linoleic acid oxidation in the presence and absence of various amino acids and with or without cupric ions. The tested amino acids have shown to possess potential pro-oxidant capacity in linoleic acid dispersed in aqueous media. The effectiveness of various amino acids on linoleic acid oxidation decreased in the following order: cysteine > serine > tryptophan > phenylalanine > histidine > alanine. The addition of alanine, serine, phenylalanine, histidine or tryptophan to linoleic acid have shown features of an autocatalytic oxidation rhain reaction. With cysteine, there was a linear relation between concentration of hydroperoxides and time during the early stages of oxidation.The pro-oxidative activity of the tested amino acids in general could be attributed to the presence of the a-amino group in the form H,-N-R. The apparent difference in the pro-oxidative activity is mainly due to the functional groups attached to @-carbon in the amino acid molecules. The addition of cupric ions at concentration of lO-5M to linoleic acid catalysed with various a-amino acids have shown that these amino acids had no significant effect. The increasing copper concentration from 10-5 to lO-3M shortened the induction period of linoleic acid catalysed by amino acids having aromatic side chain, had no effect on the induction period but increased the oxidation rate during the propagation step in the model systems catalysed by alanine and serine and in the model system containing cysteine increased the linoleic acid oxidation linearly from the start of the reaction. + I n t r o d u c t i o nPolyunsaturated fatty acids, especially those with methylene interrupted diene systems, are extremely susceptible to peroxidation and will react readily with atmospheric oxygen. Nowadays there is an increasing interest in antioxidant substances occurring in biological materials with regard to protect lipids against oxidation rather than using synthetic substances. In emulsified lipid systems, with such a large number of parameters, it is not surprising that contradictory results are sometimes obtained. For instance, the pro-and anti-oxidative activity of amino acids have been studied by several researches. R. Marcuse' and J. Sieihouiski2 found that some amino acids are effective antioxidants in emulsion.On the other hand, D. H. Saunders et a1.3 and I. / w ewicr a n d I. Solmonuior reported the reverse action.