Tocopherols

Tocopherol is the natural antioxidant of vegetable oils: it delays rancidity, and is used up while doing so [1], [2]. It comes in four forms: alpha, beta, gamma and delta. Alpha is the form that counts as vitamin E [3]. In protecting oil, alpha stands out at low doses, gamma and delta at high doses and at heat [4], [5]. More than 90% of the tocopherol in soybean oil is gamma and delta [4]. Industry gets its tocopherol from a by-product of oil refining (the cleaning of crude oil): in the deodorisation step, the fraction that is carried off by steam and condensed (the distillate) contains 3 to 9% tocopherol depending on the oil, and is concentrated [6], [7], [8]. Food and feed producers buy tocopherol as a protector of fat [9], [10], supplement producers as a source of vitamin E [11], cosmetics producers as an antioxidant and skin-care ingredient [12].

Which oil has how much?

Every seed oil has it, but the form depends on the oil. Sunflower oil carries alpha, soybean oil gamma and delta. One study measured four vegetable oils. Sunflower oil gave 432 mg/kg alpha-tocopherol and 92 mg/kg gamma. Soybean oil had 71 mg/kg alpha and 273 mg/kg gamma. Corn oil measured 173 mg/kg alpha and 260 mg/kg gamma. Canola oil had about 120 mg/kg of each [13]. So in sunflower oil alpha is about five times gamma, and in soybean oil gamma is about four times alpha [13]. The same oil also varies with variety and field: 79 soybean lines were grown at three sites for two years, and alpha, gamma, delta and total tocopherol differed by line, site and year [14]. The ratio is read from the measurement, not from the name of the oil.

Refining removes part of the tocopherol from the oil, and the removed part collects in the distillate. Across the three refining steps of sunflower oil (neutralisation, bleaching, deodorisation) 37.9% of total tocopherol was lost, with the three forms decreasing at similar rates. The loss of the last step goes into the distillate: the deodoriser distillate contained close to 29 grams of tocopherol per litre [6]. In canola oil, deodorisation alone removed 34.2% of the tocopherols [15]. The distillate is a mixed material: free fatty acids, tocopherol, sterol (the cholesterol-like component of vegetable oil), squalene and the oil itself [16]. Sunflower distillate measured 4.8% tocopherol, 9.7% sterol and 28.8% free fatty acid [7]. Soybean distillate had 9.1% tocopherol and 9.8% free sterol [8].

The concentrate is made by separating fatty acid and sterol from the distillate. Tocopherol is what remains: a 5 to 9% distillate becomes a 50 to 65% concentrate. The route is this: the fatty acids in the distillate are bound to alcohol (esterification) so that they vaporise easily, the volatile part is removed under vacuum, and tocopherol and sterols remain [17]. When the sterols are esterified with an enzyme and separated by molecular distillation (separation under very low pressure with brief heating), the main fraction obtained was 65% tocopherol [18]. Esterification, two-stage molecular distillation and crystallisation raised soybean distillate to 56.5% and two sunflower distillate samples to 20.6 and 33.9% tocopherol [19].

Alpha, gamma, delta: what is the difference?

Values are taken from PubChem. XLogP shows whether a substance is closer to oil or to water. The higher the value, the more it prefers oil. With values of 10 and above, tocopherols sit entirely on the oil side. They do not dissolve in water. The solubility of alpha-tocopherol in 70% ethanol in water was 450 times that in pure water [20]. The four forms share the same ring and the same tail. They differ in the number of small carbon arms (methyl groups) on the ring: three in alpha, two in beta and gamma, one in delta [21], [22]. While protecting the oil, tocopherol itself oxidises. One of its products is tocopherylquinone [23].

Which one is vitamin E, which one is the antioxidant? The short answer: alpha for the body, gamma and delta for the oil. The body keeps alpha and discards gamma. In oil, alpha is strong but quickly used up, while gamma and delta last longer. The European Food Safety Authority (EFSA) defines vitamin E as alpha-tocopherol only and sets an adequate intake of 13 mg a day for adult men and 11 mg for women [3]. In people given alpha and gamma at the same dose, both forms were absorbed equally from the gut, but gamma fell sharply in the blood within 24 hours. The authors concluded that the liver selects alpha [24]. In oil, the ranking depends on dose and temperature. In soybean oil, with alpha measured at its own best level (about 100 mg/kg) and gamma at its own best level (about 300 mg/kg), alpha protected 3 to 5 times more strongly [4]. At low doses alpha also leads: in tocopherol-stripped sunflower oil, alpha protected better than gamma up to 40 mg/kg and worse than gamma above 200 mg/kg [25]. At high doses and at heat, gamma and delta move ahead: in a stability test in lard at 100 °C with 0.02 and 0.1% tocopherol, protective power increased from alpha towards delta [5]. Alpha is used up fastest. In soybean oil at 50 °C, alpha decreased at 5.6% a day, gamma at 1.2% and delta at 0.5%, and alpha was gone in 16 days [1].

The natural form is one, the synthetic form is eight. Natural alpha-tocopherol is a single form, the synthetic one is a mixture of eight forms, and the body retains the natural one twice as well. The difference shows up in analysis. The natural form is known on the market as "d" (RRR), the synthetic mixture as "dl" (all-rac) [26]. According to reviews that pool labelled comparisons, the natural form is twice as potent as the synthetic mixture; the old assumption was 1.36 times [26], [27]. In analysis the two forms are told apart by the angle to which they rotate light [9].

What is it used for?

Food: it protects fat and fatty products against rancidity. Liquid oil, frying oil, sauces, fish oil, sausage: any product carrying fat goes rancid later with tocopherol. The benefit depends on the dose: too little does little, too much backfires. In soybean oil the level at which alpha-tocopherol protected best was about 100 mg/kg, for gamma about 300 mg/kg, and the natural soybean mixture gave the best result at 340 to 660 mg/kg. Above these levels, alpha, gamma and the mixture accelerated oxidation. The effect became more pronounced as the temperature rose from 40 to 60 °C [4]. In tocopherol-stripped sunflower oil, on the other hand, alpha and gamma above 20 mg/kg cut the peroxide value (the first measure of rancidity) by more than 90%, with no reversal seen up to 2,000 mg/kg [25]. With a different oil and a different test set-up, the limit changed too. In three oils kept for 56 days under supermarket conditions, soybean oil with its high share of gamma and delta oxidised later than canola and sunflower oil with their higher share of alpha [28]. In frying, the mixture beats any single form. Among tocopherols added one by one to tocopherol-stripped mid-oleic (oleic-enriched, frying-resistant) sunflower oil, gamma gave the longest frying life [29]. Oil with alpha alone deteriorated closest to the tocopherol-free oil, and chips fried in the mixture of all three came out most stable [29]. In high-oleic sunflower oil, however, a 14-day restaurant-style frying trial showed no difference between oil carrying alpha alone and oil carrying a mixture of alpha, gamma and delta; stability was decided by the share of linoleic acid (a polyunsaturated fatty acid) [30]. Highly unsaturated oil such as fish oil needs a higher dose and helpers. Delta concentrate at 2%, ascorbyl palmitate (the oil-soluble form of vitamin C) at 0.1% and lecithin at 0.5% together produced no peroxides for six months at 20 °C. Off-flavours began within three weeks [31]. It also works in meat products: fermented sausages with 200 mg tocopherol per kilogram were protected against oxidation during ripening and storage [32].

Supplements: a source of vitamin E. In a supplement, mixed tocopherols do two jobs: they put vitamin E on the label and they top up the body's gamma stores. In someone taking alpha alone, gamma falls; in someone taking the mixture, it rises. European Union supplement law lists mixed tocopherols (the mixture of the four forms) as a source of vitamin E, subject to a distribution condition [11]. In a study of 81 men, the group taking 294 mg alpha-tocopherol a day showed a 4-fold fall in gamma in cheek cells after four weeks. Mixed tocopherols with a distribution of 60% gamma, 24% delta and 14% alpha raised gamma 1.3 to 2 times [33]. 80 people with metabolic syndrome were given gamma, alpha or both for six weeks. Markers of fat oxidation fell in all three groups; one inflammation marker fell only in the group given both [34]. In a cell experiment, human red blood cells took up a mixture of gamma, delta and alpha more than alpha alone, and the mixture suppressed fat oxidation more strongly [35]. The capsule is absorbed better with a fatty meal: the same 150 mg dose gave clearly higher blood levels with a fatty breakfast (17.5 g fat) than with a low-fat breakfast (2.7 g) or with water [36]. The safe upper limit derived for adults by the EU Scientific Committee on Food is 300 mg a day [37].

Feed and pet food: the protector of fat in feed. In pet food and in feed the job is the same: it delays the rancidity of fatty feed. The European Union has authorised tocopherol extracts from vegetable oils as a technological additive (antioxidant) for all animal species. The purity requirement is at least 30% total tocopherols [10]. EFSA considered these extracts safe for the target animals and the consumer, and did not require separate proof of efficacy in feed, since the function is the same as in food [38]. The 2026 renewal assessment repeated the conclusion of safety for the target animals, the consumer and the environment [39].

Cosmetics: antioxidant and skin-care ingredient. In cosmetics, tocopherol protects the oil phase of a cream and goes on the label as a skin-care ingredient. Free tocopherol and the acetate do not do the same job: the free form is what protects the formulation, while the acetate is a reserve that is slowly released in the skin. The Cosmetic Ingredient Review (CIR) found tocopherol and its bound forms (esters such as the acetate) safe in cosmetics in its 2002 and 2018 assessments. Tocopherol has been used in formulations at up to 5%, tocopheryl acetate at up to 36% [12], [40]. The acetate is not a direct antioxidant the way free tocopherol is [41]. In rat skin, after five days of application, less than 1% of the acetate in the outer layer and about 5% in the living layer beneath had been converted to free tocopherol. This small amount was enough for ultraviolet protection in that model [41]. It has been tested together with vitamin C against sun damage: a mixture of 15% vitamin C, 1% alpha-tocopherol and 0.5% ferulic acid (a plant antioxidant) applied to human skin for four days reduced the redness caused by sun-like radiation [42].

Gamma or alpha: which form?

If the concentrate is sold diluted in a carrier oil, the certificate shows whether the percentage refers to the concentrate or to the diluted product.

Why mixed tocopherols rather than a single molecule? For the food producer, the reason is protective power at heat and at high doses: gamma and delta [5], [25]. Soybean-derived mixed tocopherols deliver both together [4]. For the supplement producer, the reason is gamma: alpha alone lowers the body's gamma, the mixture raises it [33]. The third reason is origin: the alpha in the natural mixture is a single spatial form [26].

The choice comes down to four questions.

• Protection or vitamin E? For protection, read the gamma and delta lines [5]; for a vitamin E label, read the alpha line [3]. Mixed tocopherols are a permitted source in supplements subject to the distribution condition [11] and they top up gamma [33].
• Which oil, and how much? In soybean oil the best range for the natural mixture was measured at 340 to 660 mg/kg [4]. The oil's own tocopherol counts towards the target. Soybean oil carries hundreds of mg/kg on its own [13], [1]. Raising the tocopherol of one tonne of oil by 400 mg/kg with a 56.5% concentrate takes 708 g of concentrate. The figures are an example. The oil's stability is measured by an accelerated oxidation test (Rancimat) [43].
• A supplement label? The distribution condition: gamma 50 to 70%, delta 10 to 30%, alpha below 20%, beta below 10% [11].
• Price. Total tocopherol in concentrates has been reported at 20 to 65% [18], [19]. The comparison is price per kilogram of tocopherol, not per kilogram of product. If you are paying for protection, compare on the gamma and delta lines; if for vitamin E, on the alpha line.

How to read the certificate of analysis?

Method. Four lines are expected on the certificate: alpha, beta, gamma, delta. Some laboratories report beta and gamma on a single line. That is not an error; it is a property of the column used. Tocopherols are measured by liquid chromatography (HPLC, a method that separates a mixture into its components and measures each). The oil is simply dissolved and measured, with no pre-treatment [44]. A common column type (reversed-phase) gives beta and gamma as a single peak [44]; the other type (normal-phase) gives all four forms separately [21].

Total and distribution are separate lines. Total tocopherol tells you the strength of the concentrate; the shares of the four forms tell you what it is good for. Regulation also reads the two lines separately: the food additive definition asks for the total [9], the supplement definition asks for the distribution [11].

The rotation angle shows the origin. Natural tocopherol rotates light in the positive direction; synthetic alpha-tocopherol does not rotate it. The additive specification gives at least +20° for the natural extract and 0° for synthetic alpha-tocopherol [9].

Specification and result are different things. The specification is the producer's promise; the measured value is the result for that batch. The technical data sheet (TDS) is a general document; the certificate of analysis (CoA) belongs to the batch.

What defines quality?

The distribution lines should match the source. In a soybean-derived concentrate, gamma and delta take the large share. A certificate dominated by alpha points to a sunflower origin. An alpha-dominated profile is consistent with sunflower, a gamma- and delta-dominated profile with soybean [13], [4]. If the residual sterol and fatty acid in the concentrate are low, the processing has gone further [18]. The natural extract is a brownish-red to red, viscous, clear oil. Pure tocopherols oxidise and darken in air and light [9].

Solvent residue and the origin document. Concentrate production may use no solvent at all, or it may use alcohol. The residue line on the certificate is read accordingly. For a soybean-derived product, the second question is GMO. The solvent-free route is enzyme and molecular distillation [18]. Esterification is also done with ethanol or methanol [17], [45]. Genetically modified (GMO) raw material is a labelling question: the European Union labels an ingredient produced from GMOs even when no DNA remains in it. Adventitious and technically unavoidable presence up to 0.9% is exempt [46]. A non-GMO raw-material certificate is a separate document from the certificate of analysis.

How does it behave in formulations?

Add it to fresh oil. Tocopherol delays rancidity; it does not reverse rancidity that has already started. That is why it is added while the oil is fresh. Peroxides accumulated in the oil accelerated the breakdown of tocopherol [47].

What goes alongside it? Tocopherol does not work alone. Protection increases when the oil-soluble form of vitamin C, lecithin or citric acid is added alongside it: vitamin C revives used-up tocopherol [2], and acids bind traces of metal in the oil. In oil, ascorbyl palmitate does this: in sunflower oil, ascorbyl palmitate and a phospholipid (a component of lecithin) turned alpha-tocopherol back from its oxidation product, and the three-way mixture protected better than the sum of its parts [23]. In canola oil, 200 mg/kg alpha-tocopherol with 200 mg/kg ascorbyl palmitate kept the smoke point above 170 °C through ten days of frying [48]. In refined palm oil, adding a phosphate salt to tocopherol and citric acid roughly doubled stability [49]. In fish oil, the trio of delta-tocopherol, ascorbyl palmitate and lecithin gave the strongest protection against peroxides [31].

Heat. At frying temperature, tocopherol is consumed quickly. Alpha-tocopherol loses a fixed share of what remains every hour when heated, and among the temperatures tested it was used up fastest at 180 °C [50].

Water-based products and emulsions. In an emulsion (a product in which oil is dispersed in water: cream, sauce, drink), the amount of emulsifier and the choice of vitamin C change the outcome. Excess emulsifier carries part of the tocopherol to the water side. With polysorbate 20, the protection by delta and alpha increased, and delta was carried over the most [22]. In a canola oil emulsion, 1.5 mg/kg gamma was more effective than alpha [51]. In an emulsion, vitamin C can work the other way: in an omega-3-rich emulsion, vitamin C accelerated oxidation while alpha-tocopherol slowed it [52].

The food label. Four things come up on the label: the additive code, the vitamin E percentage, the health claim and the allergen. Natural tocopherol-rich extract is the food additive with the code E306 [9]. The reference value (NRV) for the percentage on the label is 12 mg for vitamin E [53]. The claim "Vitamin E contributes to the protection of cells from oxidative stress" is authorised and may be used on food that meets the "source of vitamin E" condition (at least 15% of the reference value per 100 g or per portion) [54]. On the European Union label, natural mixed tocopherols (E306), natural alpha-tocopherol and its acetate and succinate esters from soybean sources are exempt from the soy allergen declaration [53]. The rules of other markets are read separately. EFSA found no safety concern for tocopherols as food additives (E306, E307, E308, E309) at the reported use levels [37].