Lars Åke Appelqvist

The chemistry and antioxidant properties of tocopherols and tocotrienols

This article is a review of the fundamental chemistry of the tocopherols and tocotrienols relevant to their antioxidant action. Despite the general agreement that α-tocopherol is the most efficient antioxidant and vitamin E homologuein vivo, there was always a considerable discrepancy in its “absolute” and “relative” antioxidant effectivenessin vitro, especially when compared to γ-tocopherol. Many chemical, physical, biochemical, physicochemical, and other factors seem responsible for the observed discrepancy between the relative antioxidant potencies of the tocopherolsin vivo andin vitro. This paper aims at highlighting some possible reasons for the observed differences between the tocopherols (α-, β-, γ-, and δ-) in relation to their interactions with the important chemical species involved in lipid peroxidation, specifically trace metal ions, singlet oxygen, nitrogen oxides, and antioxidant synergists. Although literature reports related to the chemistry of the tocotrienols are quite meager, they also were included in the discussion in virtue of their structural and functional resemblance to the tocopherols.

Variations in the composition of sterols, tocopherols and lignans in seed oils from fourSesamum species

Seeds from different collections of cultivatedSesamum indicum Linn and three related wild species [specifically,S. alatum Thonn.,S. radiatum Schum & Thonn. andS. angustifolium (Oliv.) Engl.] were studied for their oil contents and fatty acid composition of the total lipids. The oils from wild seeds were characterized by higher percentages of unsaponifiables (4.9, 2.6 and 3.7%, respectively) compared toS. indicum (1.4–1.8%), mainly due to their high contents of lignans. Total sterols accounted forca. 40, 22, 20 and 16% of the unsaponifiables of the four species, respectively. The four species were different in the relative percentages of the three sterol fractions (the desmethyl, monomethyl and dimethyl sterols) and in the percentage composition of each fraction. Campesterol, stigmasterol, sitosterol and Δ5-avenasterol were the major desmethyl sterols, whereas obtusifoliol, gramisterol, cycloeucalenol and citrostandienol were the major monomethyl sterols, and α-amyrin, β-amyrin, cycloartenol and 24-methylene cycloartanol were the main dimethyl sterols in all species. Differences were also observed among the four species in sterol patterns of the free sterols compared to the sterol esters.Sesamum alatum contained less tocopherols (210–320 mg/kg oil), andS. radiatum andS. angustifolium contained more tocopherols (ca. 750 and 800 mg/kg oil, respectively) than didS. indicum (490–680 mg/kg oil). The four species were comparable in tocopherol composition, with γ-tocopherol representing 96–99% of the total tocopherols. The four species varied widely in the identity and levels of the different lignans. The percentages of these lignans in the oils ofS. indicum were sesamin (0.55%) and sesamolin (0.50%).Sesamum alatum showed 1.37% of 2-episesalatin and minor amounts of sesamin and sesamolin (0.01% each).Sesamum radiatum was rich in sesamin (2.40%) and contained minor amounts of sesamolin (0.02%), whereS. angustifolium was rich in sesangolin (3.15%) and also contained considerable amounts of sesamin (0.32%) and sesamolin (0.16%).

Variation in fatty acid composition of the different acyl lipids in seed oils from fourSesamum species

Seeds from different collections of cultivatedSesamum indicum Linn. and three related wild species [specifically,S. alatum Thonn.,S. radiatum Schum and Thonn. andS. angustifolium (Oliv.) Engl.] were studied for their oil content and fatty acid composition of the total lipids. The wild seeds contained less oil (ca. 30%) than the cultivated seeds (ca. 50%). Lipids from all four species were comparable in their total fatty acid composition, with palmitic (8.2–12.7%), stearic (5.6–9.1%), oleic (33.4–46.9%) and linoleic acid (33.2–48.4%) as the major acids. The total lipids from selected samples were fractionated by thin-layer chromatography into five fractions: triacylglycerols (TAG; 80.3–88.9%), diacylglycerols (DAG; 6.5–10.4%), free fatty acids (FFA; 1.2–5.1%), polar lipids (PL; 2.3–3.5%) and steryl esters (SE; 0.3–0.6%). Compared to the TAG, the four other fractions (viz, DAG, FFA, PL and SE) were generally characterized by higher percentages of saturated acids, notably palmitic and stearic acids, and lower percentages of linoleic and oleic acids in all species. Slightly higher percentages of long-chain fatty acids (20∶0, 20∶1, 22∶0 and 24∶0) were observed for lipid classes other than TAG in all four species. Based on the fatty acid composition of the total lipids and of the different acyl lipid classes, it seems thatS. radiatum andS. angustifolium are more related to each other than they are to the other two species.

Lignan analysis in seed oils from fourSesamum species: Comparison of different chromatographic methods

Different chromatographic methods, thin-layer chromatography (TLC), gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS) and normal- and reversed-phase high-performance liquid chromatography (HPLC), were compared for their ability to separate the different lignans present in fourSesamum species,viz., S. indicum Linn.,S. alatum Thonn., S. radiatum Schum & Thonn. andS. angustifolium (Oliv.) Engl. The advantages and limitations of each method are discussed, and a combination of methods is suggested for qualitative analyses. Two-dimensional TLC was found to be a valuable qualitative technique and one-dimensional TLC is useful for preparative purposes. GC is a good supplement for qualitative analysis, but it had many limitations as a quantitative tool—it involves many preparative steps, no suitable internal standard was found to be commercially available and the various lignans had markedly different response factors. GC/MS is a necessary techniqee to confirm the identity of the lignans present. HPLC is a one-step technique suitable for quantitative analyses, and is fast and simple because it involves direct injection of oil solutions. Reversed-phase HPLC was unable to separate sesamolin and sesangolin, but a normal-phase silica column provided satisfactory separation for these two lignans. 2-Episesalation ofS. alatum, however, did not elute from the normalphase column. Once lignans are identified, a relevant HPLC method can be used for quantitative analyses. Sesamin was present in large amounts inS. radiatum, in considerable amounts inS. indicum andS. angustifolium, and in small amounts inS. alatum. Sesamolin occurred in considerable amounts inS. indicum andS. angustifolium, but only in small amounts in the other two wild species studied.Sesamum alatum was characterized by high amounts of 2-episesalatin, andS. angustifolium was characterized by high levels of sesangolin.

Further studies on lipid composition of bovine milk in relation to spontaneous oxidised flavour

Milk samples from five commercial dairy herds having severe problems with spontaneous oxidised flavour (SOF) and milk samples from five herds without such problems were analysed for parameters connected with SOF in milk. The study was directed towards analysing parameters which primarily are influenced by feeding. The fatty acid compositions of both neutral lipids and phospholipids were determined as well as the concentrations of α-tocopherol, β-carotene and copper in the milk. The samples were also analysed by dynamic headspace GC to determine volatile oxidation products. The results showed that the reasons for the occurrence of SOF in a specific herd are still obscure, since the only consistent result found for the five control herds, when compared with the corresponding experimental herd, was a higher proportion of the 18:1 trans fatty acid. However, within the affected herds, the difference between cows giving milk with off-flavour and cows giving milk without off-flavour was quite clear. In four out of five herds the ratio between antioxidants and fatty acid unsaturation was lower in milk with off-flavour, and in the fifth herd an extremely high proportion of 18: 2 in the phospholipids seemed to have been the reason for the off-flavour that developed. One of the herds also had a higher copper content in milk showing SOF. The data showed differences in importance of α-tocopherol and β-carotene, in different herds. Also the unsaturation in fatty acids of both neutral lipids and phospholipids had different importance for the flavour stability in different herds.

Thin-layer chromatographic separations of seed oil unsaponifiables from fourSesamum species

A new, two-dimensional thin-layer chromatographic system was established to provide good separation of the unsaponifiable fractions from the seed oils of three wildSesamum species, [S. alatum, Thonn.;S. radiatum, Schum and Thonn.; andS. angustifolium, (Oliv.) Engl.] and of the cultivatedS. indicum, L. The system utilizes silica gel plates and n-hexane/diethyl ether (7:3, v/v) and chloroform/diethyl ether (9:1, v/v) as mobile phases in the first and second directions, respectively. The system could be used for qualitative studies and as a preparative technique for subsequent quantitative gas chromatographic separations in chemotaxonomic and related studies onSesamum spp.

The sterol composition of freshly harvested compared to stored seeds of rape, sunflower and poppy

The composition of the free sterols and the sterol esters of freshly harvested seeds of rape, sunflower and poppy was compared to that of stored seeds. The sterol composition of rapeseed was not changed during storage, whereas in sunflower seed the free sterols had less of Δ5-avenasterol and Δ7-stigmastenol in ten-month-old seeds compared to fresh seeds. The greatest relative changes were observed for esterified sterols in poppy seed, with a drop in the percentage of Δ5-avenasterol from 25.3% in freshly harvested to 16.9% in seeds stored for 10 months.