Sesame seed and its lignans produce marked enhancement of vitamin E activity in rats fed a low α-tocopherol diet

Three series of experiments demonstrated that sesame seed and its lignans cause significant elevation of α-tocopherol content in rats. In Experiment 1, 20% sesame seed (with a negligible amount of α-tocopherol) supplementing 10 (low), 50 (normal), or 250 (high) mg/kg α-tocopherol diets (protein and fat concentrations in diets were adjusted to 200 and 110 g/kg, respectively) all caused a significant increase of α-tocopherol in the blood and tissue of rats. In Experiment 2, groups of rats were fed five different diets: a vitamin E-free control diet, a low α-tocopherol diet, and three low α-tocopherol diets supplemented with 5, 10, and 15% sesame seed. Changes in lipid peroxides in liver, red blood cell hemolysis, and pyruvate kinase activity, as indices of vitamin E deficiency, were examined. These indices were high in the low α-tocopherol diet, whereas supplementation with even 5% sesame seed suppressed these indices completely and caused a significant increase of α-tocopherol content in the plasma and liver. In Experiment 3 two diets containing sesame lignan (sesaminol or sesamin) and low α-tocopherol were tested. Results in both of the sesame lignan-fed groups were comparable to those observed in the sesame seed-fed groups as shown in Experiment 2. These experiments indicate that sesame seed lignans enhance vitamin E activity in rats fed a low α-tocopherol diet and cause a marked increase in α-tocopherol concentration in the blood and tissue of rats fed an α-tocopherol-containing diet with sesame seed or its lignans.     

Effects of various tocopherol-containing diets on tocopherol secretion into bile

γ-Tocopherol is abundant in common vegetable oil, but its concentration in plasma and liver is much lower than that of α-tocopherol. Discrimination between different forms of tocopherol is thought to take placevia the hepatic α-tocopherol transfer protein (α-TTP). γ-Tocopherol, with a low binding capacity to α-TTP, is thought to be excretedvia the bile. Our previous studies showed that γ-tocopherol administered with sesame seed exhibits significantly higher concentrations in the plasma and liver of rats than γ-tocopherol alone. Thus, we attempted to confirm whether a much higher amount of γ-tocopherol rather than γ-tocopherol would be secreted in the bile, and whether sesame seed would suppress the secretion of γ-tocopherol. In one experiment, we examined the concentrations of α-or γ-tocopherol in the plasma, liver, and bile of rats fed diets containing 300 mg/kg of α-tocopherol, 300 mg/kg of γ-tocopherol, or 300 mg/kg each of α-tocopherol+γ-tocopherol, and in the other experiment, we compared the γ-tocopherol concentrations of rats fed a diet of γ-tocopherol alone to those of rats fed a γ-tocopherol+sesame seed diet (each diet contained 300 mg/kg γ-tocopherol). The bile collection was done over 6 h. The γ-tocopherol concentration in the bile was markedly lower than that of α-tocopherol, paralleling the concentrations in the plasma and liver. Intake of α-tocopherol and γ-tocopherol together further lowered the concentration of γ-tocopherol in the bile as well as in the plasma and liver, compared to the intake of γ-tocopherol alone. The γ-tocopherol concentration in the bile, as well as in the plasma and liver, was markedly higher in the sesame seed-fed group than in the γ-tocopherol alone group. We found that the concentrations of α- or γ-tocopherol in the bile showed a good correlation with the concentrations of α- or γ-tocopherol in the liver, though the concentrations in the bile were substantially lower than those in the liver. These findings suggest that secretion into the bile is not a major metabolic route of α- or γ-tocopherol.     

Effect of sesaminol on plasma and tissue alpha-tocopherol and alpha-tocotrienol concentrations in rats fed a vitamin E concentrate rich in tocotrienols

We have shown that sesame lignans added to rat diet resulted in significantly greater plasma and tissue concentrations of α- and γ-tocopherol concentrations in supplemented rats than in rats without supplementation. In the present studies we examined whether sesaminol, a sesame lignan, enhances tocotrienol concentrations in plasma and tissues of rats fed diets containing a tocotrienol-rich fraction of palm oil (T-mix). In Ex-periment 1, effects of sesaminol on tocotrienol concentrations in plasma, liver, and kidney were evaluated in rats fed diets containing 20 mg/kg of T-mix (20T) and 50 mg/kg of T-mix (50T) with or without 0.1% sesaminol. Although the T-mix contained 23% α-tocopherol, 22% α-tocotrienol, and 34% γ-tocotrienol, α-tocopherol constituted most or all of the vitamin E in plasma and tissue (from 97% in kidney to 100% in plasma), with no or very little α-tocotrienol and no γ-tocotrienol at all. Addition of sesaminol to the T-mix resulted in significantly higher plasma, liver, and kidney α-tocopherol concentrations compared to values for T-mix alone. Further, T-mix with sesaminol resulted in significantly higher α-tocotrienol concentrations in kidney, although the concentration was very low. In Experiment 2, we examined whether sesaminol caused enhanced absorption of α-tocopherol and α-tocotrienol in a dosage regimen supplying T-mix and sesaminol on alternating days and observed significantly higher levels of α-tocopherol and α-tocotrienol in rats fed sesaminol, even without simultaneous intake, compared to those in rats without sesaminol. In Experiment 3, α-tocopherol was supplied to the stomach with and without sesaminol, and α-tocopherol concentrations in the lymph fluid were measured, α-Tocopherol concentrations were not different between groups. These results indicated that sesaminol produced markedly higher α-tocopherol concentrations in plasma and tissue and significantly greater α-tocotrienol concentrations in kidney and various other tissues, but the concentrations of α-tocotrienol were extremely low compared to those of α-tocopherol (Exps. 1 and 2). However, the sesaminol-induced increases of α-tocopherol and α-tocotrienol concentrations in plasma and tissue were not caused by their enhanced absorption since sesaminol did not enhance their absorption.     

Sesamin (a compound from sesame oil) increases tocopherol levels in rats fedad libitum

Six groups of rats were fed diets low, but adequate, in α-tocopherol but high in γ-tocopherol. The six diets differed only in their contents (0, 0.25, 0.5, 1.0, 2.0, and 4.0 g/kg, respectively) of sesamin, a lignan from sesame oil. After four weeks ofad libitum feeding, the rats were sacrificed and the concentrations of α- and γ-tocopherols were measured in the plasma, livers, and lungs. Sesamin-feeding increased γ-tocopherol and γ-/α-tocopherol ratios in the plasma (P<0.05), liver (P<0.001), and lungs (P<0.001). The increase was non-significant for α-tocopherol. Thus, sesamin appears to spare γ-tocopherol in rat plasma and tissues, and this effect persists in the presence of α-tocopherol, a known competitor to γ-tocopherol. This suggests that the bioavailability of γ-tocopherol is enhanced in phenol-containing diets as compared with purified diets.     

Effect of dietary carnosine on plasma and tissue antioxidant concentrations and on lipid oxidation in rat skeletal muscle

The effect of dietary carnosine supplementation on plasma and tissue carnosine and α-tocopherol concentrations and on the formation of thiobarbituric acid reactive substances (TBARS) in rat skeletal muscle homo-genates was evaluated. Plasma, heart, liver and hind leg muscle was obtained from rats fed basal semipurified diets or basal diets containing carnosine (0.0875%), α-tocopheryl acetate (50 ppm), or carnosine (0.0875%) plusα-tocopheryl acetate (50 ppm). Dietary carnosine supplementation did not increase carnosine concentrations in heart, liver and skeletal muscle. Dietary supplementation with both carnosine and α-tocopherol increased carnosine concentrations in liver 1.56-, 1.51- and 1.51-fold as compared with diets lacking carnosine, α-tocopherol or both carnosine and α-tocopherol, respectively. Dietary supplementation with both carnosine and α-tocopherol also increased α-tocopherol concentrations in heart and liver 1.38-fold and 1.68-fold, respectively, as compared to supplementation with α-tocopherol alone. Dietary supplementation with carnosine, α-tocopherol or both car-nosine and α-tocopherol was effective in decreasing the formation of TBARS in rat skeletal muscle homogenate, with dietary α-tocopherol and α-tocopherol plus carnosine being more effective than dietary carnosine alone. The data suggest that dietary supplementation with carnosine and α-tocopherol modulates some tissue carnosine and α-tocopherol concentrations and the formation of TBARS in rat skeletal muscle homogenates.     

γ-tocotrienol as a hypocholesterolemic and antioxidant agent in rats fed atherogenic diets

This study was designed to determine whether incorporation of γ-tocotrienol or α-tocopherol in an atherogenic diet would reduce the concentration of plasma cholesterol, triglycerides and fatty acid peroxides, and attenuate platelet aggregability in rats. For six weeks, male Wistar rats (n=90) were fed AIN76A semisynthetic test diets containing cholesterol (2% by weight), providing fat as partially hydrogenated soybean oil (20% by weight), menhaden oil (20%) or corn oil (2%). Feeding the ration with menhaden oil resulted in the highest concentrations of plasma cholesterol, low and very low density lipoprotein cholesterol, triglycerides, thiobarbituric acid reactive substances and fatty acid hydroperoxides. Consumption of the ration containing γ-tocotrienol (50 μ/kg) and α-tocopherol (500 mg/kg) for six weeks led to decreased plasma lipid concentrations. Plasma cholesterol, low and very low density lipoprotein cholesterol, and triglycerides each decreased significantly (P<0.001). Plasma thiobarbituric acid reactive substances decreased significantly (P<0.01), as did the fatty acid hydroperoxides (P<0.05), when the diet contained both chromanols. Supplementation with γ-tocotrienol resulted in similar, though quantitatively smaller, decrements in these plasma values. Plasma α-tocopherol concentrations were lowest in rats fed menhaden oil without either chromanol. Though plasma α-tocopherol did not rise with γ-tocotrienol supplementation at 50 mg/kg, γ-tocotrienol at 100 mg/kg of ration spared plasma α-tocopherol, which rose from 0.60±0.2 to 1.34±0.4 mg/dL (P<0.05). The highest concentration of α-tocopherol was measured in plasma of animals fed a ration supplemented with α-tocopherol at 500 mg/kg. In response to added collagen, the partially hydrogenated soybean oil diet without supplementary cholesterol led to reduced platelet aggregation as compared with the cholesterol-supplemented diet. However, γ-tocotrienol at a level of 50 mg/kg in the cholesterol-supplemented diet did not significantly reduce platelet aggregation. Platelets from animals fed the menhaden oil diet released less adenosine triphosphate than the ones from any other diet group. The data suggest that the combination of γ-tocotrienol and α-tocopherol, as present in palm oil distillates, deserves further evaluation as a potential hypolipemic agent in hyperlipemic humans at atherogenic risk.     

Influence of dietary supplementation with long-chain n−3 or n−6 polyunsaturated fatty acids on blood inflammatory cell populations and functions and on plasma soluble adhesion molecules in healthy adults

Greatly increasing the amounts of flaxseed oil [rich in α-linolenic acid (ALNA)] or fish oil (FO); [rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] in the diet can decrease inflammatory cell functions and so might impair host defense. The objective of this study was to determine the effect of dietary supplementation with moderate levels of ALNA, γ-linolenic acid (GLA), arachidonic acid (ARA), DHA, or FO on inflammatory cell numbers and functions and on circulating levels of soluble adhesion molecules. Healthy subjects aged 55 to 75 yr consumed nine capsules per day for 12 wk. The capsules contained placebo oil (an 80∶20 mix of palm and sunflowerseed oils) or blends of placebo oil with oils rich in ALNA, GLA, ARA, or DHA or FO. Subjects in these groups consumed 2 g ALNA; approximately 700 mg GLA, ARA, or DHA; or 1 g EPA plus DHA (720 mg EPA+280 mg DHA) daily from the capsules. Total fat intake from the capsules was 4 g per day. None of the treatments affected inflammatory cell numbers in the bloodstream; neutrophil and monocyte phagocytosis or respiratory burst in response to E. coli; production of tumor necrosis factor-α, interleukin-1β, and interleukin-6 in response to bacterial lipopolysaccharide; or plasma concentrations of soluble intercellular adhesion molecule-1. In contrast, the ALNA and FO treatments decreased the plasma concentrations of soluble vascular cell adhesion molecule-1 (16 and 28% decrease, respectively) and soluble E-selectin (23 and 17% decrease, respectively). It is concluded that, in contrast to previous reports using higher amounts of these fatty acids, a moderate increase in consumption of long-chain n−6 or n−3 polyunsaturated fatty acids does not significantly affect inflammatory cell numbers or neutrophil and monocyte responses in humans and so would not be expected to cause immune impairment. Furthermore, we conclude that moderate levels of ALNA and FO, which could be incorporated into the diet, can decrease some markers of endothelial activation and that this mechanism of action may contribute to the reported health benefits of n−3 fatty acids.     

Fractionation of blackcurrant seed oil

Blackcurrant seed oil is known to be one of the richest natural sources of γ-linolenic (allcis-6,9,12-octadecatrienoic) acid, with values of up to 20% of this acid. These concentrations are sufficient for most applications of the oil, but some utilizations require higher concentrations of γ-linolenic acid. Blackcurrant seed oil also contains up to 14%α-linolenic (allcis-9,12,15-octadecatrienoic) acid. Different fractionation techniques have been evaluated to separate γ-linolenic acid specifically from the other fatty acids present in the oil and, in particular, fromα-linolenic acid. Distillation as well as fractionated crystallization at various temperatures did not give any reasonable results. Surprisingly enough, urea fractionation in methanol gives a specific separation ofα- and γ-linolenic acid, whereas stearidonic (allcis-6,9,12,15-octadecatetraenoic) acid, which is present at around 3% in the blackcurrant seed oil, cannot be separated by urea fractionation. Stearidonic acid, like γ-linolenic acid, has a double bond in the Δ6 position, which makes these two acids unique in this respect. This most probably explains their similar behavior toward urea-occlusion. Further semi-industrial preparative HPLC separations allowed us to obtain fractions of 95% γ-linolenic acid.     

Evening primrose (Oenothera spp.) oil and seed

Evening primrose (Oenothera spp.) seed contains ca. 15% protein, 24% oil, and 43% cellulose plus lignin. The protein is unusually rich in sulphur-containing amino acids and in tryptophan. The component fatty acids of the oil are 65–80% linoleic and 7–14% ofγ-linolenic, but noα-linolenic acid. The 1.5–2% unsaponifiable matter has a composition very similar to that of cottonseed oil. The sterol fraction contains 90%β-sitosterol and the 4-methyl sterol fraction contains 48% citrostadienol;γ-tocopherol dominates its class, with someα- but no other tocopherols.     

Gender and dietary fat affect α-tocopherol status in F344/N rats

For four weeks, groups of eight male and eight female F344/N rats were fed diets containing 15.5, 20, 30 or 40% of energy (en%) as fat. The fat was composed of corn oil and beef tallow with 9 en% from linoleate in all diets. Females had greater mean hepatic α-tocopherol levels, whereas males had greater plasma α-tocopherol and cholesterol concentrations. In males, the plasma ratio of α-tocopherol/cholesterol was significantly greater than in females (P<0.05). Plasma α-tocopherol increased with increasing en% fat (r=0.51,P<0.001) in both sexes, but dietary fat did not alter hepatic α-tocopherol levels. These results suggest that plasma α-tocopherol may serve as a biomarker of total dietary fat intake and that in F344/N rats gender differences affect α-tocopherol and cholesterol status.     

Plasma and lipoprotein lipid peroxidation in humans on sunflower and rapessed oil diets

The effects of natural mixed diets on lipid peroxidation were investigated in humans. In the first study, 59 subjects were fed a rapeseed oil-based diet rich in monounsaturated fatty acids (MUFA) and a sunflower oil-based diet rich in polyunsaturated fatty acids (PUFA) in a cross-over manner for three and a half weeks. The lipid peroxidation products in plasma were determined by measuring conjugated dienes and malondialdehyde (MDA). In a second study, plasma thiobarbituric acid reactive substances (TBARS), lipid hydroperoxides, and the susceptibility of very low density lipoprotein + low-density lipoprotein (LDL) toin vitro oxidation were measured from subjects fed similar MUFA and PUFA diets for six week diets. No significant differences in plasma MDA or conjugated diene concentrations were found after the rapeseed oil diet or the sunflower oil diet in Study 1. In the second study, a small but significant decrease (P<0.05) in both lipid hydroperoxides and TBARS was observed in the LDL fraction after the sunflower oil diet. Thein vitro oxidation gave opposite results, showing increased oxidation after the sunflower oil diet. Despite a high intake of α-tocopherol during the oil peroids, no increase in plasma α-tocopherol was noticed in either study. The results suggest that moderate changes in the fatty acid composition in the Western-type diet may be adequate to affect lipoprotein susceptibility to oxidationin vitro, but there is considerable disparity with some indices ofin vivo lipid peroxidation.     

Lignans and tocopherols in Indian sesame cultivars

Lignan (sesamol, sesamin, and sesamolin) profile was determined in different cultivars (botanically identified or market samples) of sesame seeds and commercial oils procured from different parts of India. The wide variation observed in total lignans from 21 sesame seed and 9 commercial oils was attributed to variations in sesamin and sesamolin contents. Lignan content was high (18 g sesamin/kg, 10 g sesamolin/kg) in seasame cultivars obtained from the northeastern states of India. In two of the commercial oils having the Agmark label, the total lignan content was ∼12 g/kg (7.3 g sesamin, 4.7 g sesamolin), 50% of the maximum permissible levels of unsaponifiable matter. In both the seeds and commercial oils, γ-tocopherol was the only representative of tocopherol isomers identified. Sesamin and sesamolin were isolated and crystallized from high-lignan cultivars, and their purity was confirmed by HPLC and spectral (UV and fluorescence) analysis.     

Comparative uptake of α- and γ-tocopherol by human endothelial cells

The intake of γ-tocopherol by North Americans is generally higher than that of α-tocopherol. However, the levels of α-tocopherol in human blood have consistently been shown to be higher than those of γ-tocopherol suggesting differential cellular retention of the two tocopherol forms. We sought to resolve this question by studying tocopherol metabolism by human endothelial cells in culture. The time- and dose-dependent uptake of γ-tocopherol by endothelial cells was similar to that of α-tocopherol. To determine the comparative uptake between α- and γ-tocopherol, we adopted two approaches in which cells were enriched with either increasing concentrations of an equimolar mixture of α- and γ-tocopherol; or cells were enriched with a fixed concentration of tocopherols in which the α to γ ratio was varied. Our results indicated that there was a preferential uptake of γ-tocopherol by the cells. When cells were enriched with either α- or γ-tocopherol and the disappearance of individual tocopherols was monitored over time, γ-tocopherol exhibited a faster rate of disappearance. The faster turnover of γ-tocopherol can explain the discrepancy between high intake and low retention of γ-tocopherol in man.     

Cytochrome P450-Dependent Metabolism of Vitamin E Isoforms is a Critical Determinant of Their Tissue Concentrations in Rats

The aim of this study was to clarify the contribution of cytochrome P450 (CYP)-dependent metabolism of vitamin E isoforms to their tissue concentrations. We studied the effect of ketoconazole, a potent inhibitor of CYP-dependent vitamin E metabolism in cultured cells, on vitamin E concentration in rats. Vitamin E-deficient rats fed a vitamin E-free diet for 4 weeks were administered by oral gavage a vitamin E-free emulsion, an emulsion containing α-tocopherol, γ-tocopherol or a tocotrienol mixture with or without ketoconazole. α-Tocopherol was detected in the serum and various tissues of the vitamin E-deficient rats, but γ-tocopherol, α- and γ-tocotrienol were not detected. Ketoconazole decreased urinary excretion of 2,5,7,8-tetramethyl-2(2′-carboxyethyl)-6-hydroxychroman after α-tocopherol or a tocotrienol mixture administration, and that of 2,7,8-trimethyl-2(2′-carboxyethyl)-6-hydroxychroman (γ-CEHC) after γ-tocopherol or a tocotrienol mixture administration. The γ-tocopherol, α- and γ-tocotrienol concentrations in the serum and various tissues at 24 h after their administration were elevated by ketoconazole, while the α-tocopherol concentration was not affected. The γ-tocopherol or γ-tocotrienol concentration in the jejunum at 3 h after each administration was also elevated by ketoconazole. In addition, significant amount of γ-CEHC was in the jejunum at 3 h after γ-tocopherol or γ-tocotrienol administration, and ketoconazole inhibited γ-tocopherol metabolism to γ-CEHC in the jejunum. These results showed that CYP-dependent metabolism of γ-tocopherol and tocotrienol is a critical determinant of their concentrations in the serum and tissues. The data also suggest that some amount of dietary vitamin E isoform is metabolized by a CYP-mediated pathway in the intestine during absorption.     

Tissue Distribution of α- and γ-Tocotrienol and γ-Tocopherol in Rats and Interference with Their Accumulation by α-Tocopherol

The aim of this study was to evaluate tissue distribution of vitamin E isoforms such as α- and γ-tocotrienol and γ-tocopherol and interference with their tissue accumulation by α-tocopherol. Rats were fed a diet containing a tocotrienol mixture or γ-tocopherol with or without α-tocopherol, or were administered by gavage an emulsion containing tocotrienol mixture or γ-tocopherol with or without α-tocopherol. There were high levels of α-tocotrienol in the adipose tissue and adrenal gland, γ-tocotrienol in the adipose tissue, and γ-tocopherol in the adrenal gland of rats fed tocotrienol mixture or γ-tocopherol for 7 weeks. Dietary α-tocopherol decreased the α-tocotrienol and γ-tocopherol but not γ-tocotrienol concentrations in tissues. In the oral administration study, both tocopherol and tocotrienol quickly accumulated in the adrenal gland; however, their accumulation in adipose tissue was slow. In contrast to the dietary intake, α-tocopherol, which has the highest affinity for α-tocopherol transfer protein (αTTP), inhibited uptake of γ-tocotrienol to tissues including adipose tissue after oral administration, suggesting that the affinities of tocopherol and tocotrienol for αTTP in the liver were the critical determinants of their uptake to peripheral tissues. Vitamin E deficiency for 4 weeks depleted tocopherol and tocotrienol stores in the liver but not in adipose tissue. These results indicate that dietary vitamin E slowly accumulates in adipose tissue but the levels are kept without degradation. The property of adipose tissue as vitamin E store causes adipose tissue-specific accumulation of dietary tocotrienol.     

Inhibition of oxidation in 10% oil-in-water emulsions by β-carotene with α- and γ-tocopherols

The effects of low concentrations of β-carotene, α-, and γ-tocopherol were evaluated on autoxidation of 10% oil-in-water emulsions of rapeseed oil triacylglycerols. At concentrations of 0.45, 2, and 20 μg/g, β-carotene was a prooxidant, based on the formation of lipid hydroperoxides, hexanal, or 2-heptenal. In this emulsion, 1.5, 3, and 30 μg/g of γ-tocopherol, as well as 1.5 μg/g of α-tocopherol, acted as antioxidants and inhibited both the formation and decomposition of lipid hydroperoxides. Moreover, at a level of 1.5 μg/g, γ-tocopherol was more effective as an antioxidant than α-tocopherol. At levels of 0.5 μg/g, both α- and γ-tocopherol significantly inhibited the formation of hexanal but not the formation of lipid hydroperoxides. Oxidation was effectively retarded by combinations of 2 μg/g β-carotene and 1.5 μg/g γ- or α-tocopherol. The combination of β-carotene and α-tocopherol was significantly better in retarding oxidation than α-tocopherol alone. While γ-tocopherol was an effective antioxidant, a synergistic effect between β-carotene and γ-tocopherol could not be shown. The results indicate that there is a need to protect β-carotene from oxidative destruction by employing antioxidants, such as α- and γ-tocopherol, should β-carotene be used in fat emulsions.     

Distribution of α-and γ-tocopherols in Atlantic salmon (Salmo salar) tissues

Groups of Atlantic salmon parr (mean initial weight 9.5 g) were fed three diets, the first containing no tocopherol supplement, the others supplemented with either all-rac-α-tocopherol (A-T) or RRR-γ-tocopherol (G-T). Tocopherol concentrations in the liver, serum, testes, kidney, brain, gill, muscle, and perivisceral fat were measured after 36 wk. Despite a higher dietary intake of G-T, compared to A-T, deposition of γ-tocopherol (γT) was less efficient than of α-tocopherol (αT) in most tissues except in the perivisceral fat, an adipose tissue. In fish fed the G-T diet, the γT/αT ratio was highest in the perivisceral fat and lowest in the liver, indicating that the liver is the most discriminatory organ for retaining αT as compared to γT, and the perivisceral fat is more suitable for the storage of γT. A negative correlation (P<0.01) was observed between the γT/αT ratio and the corresponding tissue phospholipid content, suggesting that γT is less efficiently deposited compared to αT in the phospholipid-rich membranes which are presumed to be the functional site for lipid antioxidants in vivo. During restricted intake of αT, the liver and muscle exhibited the greatest reduction of this tocopherol among the tissues analyzed. The presence of minimal αT in the muscle from fish fed the tocopherol-unsupplemented diet led to greater susceptibility to lipid peroxidation after frozen storage than was the case for muscle containing higher concentrations of either αT or γT. However, both αT and γT were effective stabilizers of salmon muscle lipids during frozen storage. Presented in part at the Annual Meeting of the American Oil Chemists' Society, San Antonio, Texas, May 1995.     

Autoxidation of linoleic acid and behavior of its hydroperoxides with and without tocopherols

The autoxidation of linoleic acid dispersed in an aqueous media and the effect of α-, γ- and δ-tocopherols were studied. The quantitative analysis of the hydroperoxide isomers (13-cis,trans; 13-trans,trans; 9-trans,cis; 9-trans,trans) by direct high-performance liquid chromatography exhibited a prooxidant activity of α-tocopherol at high concentration (3.8% by weight of linoleic acid). On the other hand, α-tocopherol at lower concentrations (0.38 and 0.038%) and γ- and δ-tocopherols at high concentration (3.8%) were antioxidant. Furthermore, the addition of tocopherols modified the distribution of the geometrical isomers. The formation of thetrans,trans hydroperoxide isomers was completely inhibited by the highest concentration of the three tocopherols independently of their antioxidant or prooxidant activity and only delayed by the lower concentrations of α-tocopherol. The addition of tocopherols to hydroperoxide isomers reduced the decomposition rate of these isomers in the order α-tocopherol < γ-tocopherol < δ-tocopherol for thecis,trans hydroperoxide isomer and α-tocopherol ≪ γ-tocopherol ⋍ δ-tocopherol for thetrans,trans hydroperoxide isomer. With these hydroperoxides, as during linoleic acid autoxidation, α-tocopherol was completely oxidized whatever its initial concentration, while γ-tocopherol underwent partial oxidation and δ-tocopherol was practically unchanged.     

Acyl group distributions in tissue lipids of rats fed evening primrose oil (λ-linolenic plus linoleic acid) or soybean oil (α-linolenic plus linoleic acid)

Three groups of rats were fed diets with either 10 weight percent (wt%) of evening primrose oil, safflower oil or soybean oil for 11 weeks. Diets contained 7.1 wt% linoleic acid +0.8 wt% γ-linolenic acid, 7.6 wt% linoleic acid, or 5.3 wt% linoleic acid +0.7 wt% α-linolenic acid, respectively. In liver mitochondria as well as in heart, dietary γ-linolenic acid did not affect the fatty acid profiles of phosphatidylcholnes (PC), phosphatidylethanolamines (PE) or cardiolipins (CL), whereas dietary α-linolenic acid caused an increased formation of (n−3) polyunsaturated fatty acids (PUFA). The liver Δ6− and Δ5-desaturase activities determined in vitro were not affected by the dietary fats. In brain PE, which are rich in C22− and C20-(n−3) PUFA, as well as in testes PC and PE, which are rich in (n−6) PUFA, no effects were found from a partial replacement of dietary linoleic acid with γ-linolenic acid or α-linolenic acid. In kidney PC, PE, phosphatidylinositol (PI) and CL, 20∶3(n−6) was moderately elevated to ca. 1% following intake of γ-linolenic acid, whereas partial replacement of linoleic acid with α-linolenic acid was followed by increased deposition of 22∶6(n−3) in PC and PE of testes and kidney. Thus, no general effect of evening primrose oil on the content of (n−6) PUFA in rat tissue phospholipids was observed, wheras a significant incorporation of γ-linolenic acid into liver and adipose tissue triglycerides was found.     

Oxidative stability of flaxseed lipids during baking

This study examined the stability of whole and ground flaxseed, either alone or as an ingredient in a muffin mix, by measuring oxygen consumption and changes in α-linolenic acid under various conditions. When ground flaxseed was heated at 178°C in a sealed tube, headspace oxygen decreased from 21 to 2% within 30 min, while that of whole flaxseed decreased only slightly up to 90 min at 178°C. Under the same conditions, the oxygen consumption of lipids extracted from an equivalent amount of flaxseed was between the whole flaxseed and the ground flaxseed. After heating to 178°C for 1.5 h, α-linolenic acid decreased from 55.1 to 51.3% in ground flaxseed, and to 51.7% in lipid extracts, but it remained unchanged in the whole flaxseed. Ground flaxseed with large (<20 mesh) or small (>35 mesh) particle size absorbed more oxygen than samples with medium particle size when heated at 122°C for 8 h. Long-term storage of whole or ground flaxseed or lipid extracts showed that all three preparations were stable at room temperature for 280 d with 12 h light/dark cycles. A muffin mix, containing 28.5 wt% flaxseed flour, consumed oxygen more rapidly than a control muffin without flaxseed flour at a baking temperature of 178°C for 2 h, but the α-linolenic acid remained unchanged in both muffin mixes. Polymers derived from triglyceride oxidation and newtrans isomers of α-linolenic acid were not detected under the present experimental conditions. Under typical baking conditions, there is minimal loss of α-linolenic acid from flaxseed, although the manner of incorporation of flaxseed in food products should be considered to minimize oxidation of α-linolenic acids.