H. S. Olcott

A weighing method for measuring the induction period of marine and other oils

SummaryA convenient method for measuring the length of the induction period of marine and other oils and unsaturated fatty acid esters depends upon determining the increases in weight. Small amounts of oil with or without additives are held in constant temperature ovens and weighed at regular intervals. Some of the details of technique are described.

POSITIONAL DISTRIBUTION OF FATTY ACIDS IN FISH AND OTHER ANIMAL LECITHINS.

Abstract Phosphatidyl choline (lecithin) fractions were prepared from tuna, salmon, and menhaden muscle, from egg yolk, and from rat and beef liver. Hydrolysis by snake-venom phospholipase A (phosphatide acyl-hydrolase, EC 3.1.1.4) was used to determine the positional distribution of the fatty acids. The fatty acid composition of the hydrolyzed fatty acids (β position) and those remaining with the phosphatidyl moiety (α′ position) were separately determined by gas-liquid chromatography of the methyl esters. 36–86 mole % of the fatty acids esterified in the α′ position were saturated; 91–99 mole % of the fatty acids in the β position were unsaturated. Palmitic and stearic acids were the predominant saturated acids in the α′ position. Some similarity was noted in the β-position distribution of linoleic, arachidonic, eicosapentaenoic, docosaenoic, docosapentaenoic, and docosahexaenoic acids. This observation tends to support the hypothesis of the intechangeability of linoleic and arachidonic acids with “non-essential” polyenoic acids.

Effect of heme compounds on lipid oxidation

By polarographic oxygen analyzer, the rate of oxidation of linoleate solutions was catalyzed by low concentrations of heme and heme-proteins and inhibited by higher concentrations. High concentrations of these substances also inhibited lipoxygenase catalysis of linoleate oxidation. Manganese and cobalt salts inhibited heme-catalyzed linoleate oxidation. These combined effects may reflect the oxidative synthesis of antioxidants from heme compounds.

Catalysis of unsaturated lipid oxidation by iron protoporphyrin derivatives

Abstract Various derivatives of hemoglobin and myoglobin, including methemoglobin and metmyoglobin; imidazole hemoglobin hemichrome and imidazole myoglobin hemichrome; carbon monoxide hemoglobin; oxyhemoglobin; and nitric oxide hemoglobin were used as catalysts for unsaturated lipid oxidation. All were active catalysts, but there were induction periods with some of the ferrous forms. Experiments in which catalysts were extracted from oxidizing mixtures and examined spectrophotometrically indicated that the ferrous forms of the hematin compounds were converted to the ferric form at the time of extraction. Denatured methemoglobin and nitric oxide hemoglobin behaved similarly to the analogous native protein compounds.

The lipids of krill (Euphausia species) and red crab (Pleuroncodes planipes)

The composition of the lipids of two samples of krill and one of “red crab” was determined by thin layer, column and gas chromatographic procedures. A large number of unusual fatty acids were present.

Stable Nitroxides as Lipid Antioxidants

STABLE nitroxides have been shown by Neiman et al.1,2 and Brownlie and Ingold3 to be inhibitors of polymerization. Hoffman4 mentioned that di-t-butyl nitroxide was an effective antioxidant, polymerization inhibitor and radical trap, but no details were given. According to Neiman et al.1 and Brownlie and Ingold3 the nitroxide radical reacts with an alkyl radical, stopping the chain reaction as follows The nitroxides compete favourably with oxygen for the R radical1, and propagation is said to be prevented with little or no peroxide formation. Work in this laboratory5 suggested that nitroxide radicals were involved in the antioxidant activity of secondary aliphatic hydroxyl-amines toward unsaturated lipids. Some of the known stable nitroxide radicals have now been examined.

Comparison of antioxidant activities of tocol and its methyl derivatives

In tests with purified menhaden oil at 37C and with squalene at 37C and 50C, unsubstituted tocol, 7,8-dimethyl tocol (γ-tocol), and 8-methyl tocol (σ-tocol) were superior antioxidants to 5,7-dimethyl tocol and 5,7,8-trimethyl tocol (α-tocol). In contrast to previous reports, there were no differences in the order of the activities of the tocopherols at different temperatures.

An antagonistic effect with antioxidants for unsaturated fats

Summaryα-and γ-tocopherol act as pro-oxidants with marine oils containing the antioxidant EMQ. The term “antagonism” is suggested for such phenomena. Antagonism was also demonstrable in purified unsaturated fatty ester acids and triglycerides. Nitrogenous inhibitors (EMQ, DPPD, ADA) are more affected by added tocopherols than are the phenolic antioxidants examined (BHT, BHA, PG, NDGA). Phenolic antioxidants other than tocopherols do not show marked antagonism with EMQ.

Phospholipids of tuna white muscle

The composition of the lipids from the white muscle of five tuna fish has been determined. Total extractable lipid varied from 0.5%–10.3% of the tissue wet weight; phospholipid content ranged from 0.3%–0.6%. The separation of the phospholipid components was made by column chromatography with activated silicic acid and stepwise elution, with increasing concentrations of methanol in chloroform. The components were identified by chemical tests and infrared (IR) spectra. Tuna white musele contained an average of 0.5% phospholipid on wet weight basis; 23% was cephalin, 54% lecithin, 8% sphingomyelin, 2% phosphoinositide, with small amounts of unidentified components. Ten to 30% of the lecithin and cephalin fractions were in the form of plasmalogens. The gas-liquid chromatographic analyses of the 12–22 carbon fatty acids of the lecithin, cephalin, and neutral fractions are presented. The cephalins were characteristically high in stearie acid and low in palmitic acid, in contrast to the lecithins.

Reaction of aliphatic tertiary amines with hydroperoxides

Trioctylamine acts as an antioxidant in fats at 70C but not at lower temperatures. A reactive antioxidant intermediate was sought. Dioctylhydroxylamine was obtained from the reaction of trioctylamine and t-butyl peroxide at 70C. The recrystallized product had antioxidant properties. About 0.1% existed as stable free radical by electron-spin resonance. Didecyl- and didodecylhydroxylamines were also synthesized from the corresponding tertiary amines. These and a sample of commercial diethylhydroxylamine also contained free radicals and possessed antioxidant activity.