What is wheat germ oil, and what does it contain?

Wheat germ oil is the oil in wheat germ, the small embryo of the wheat grain that is separated from the rest of the grain when wheat is milled into flour. The germ makes up only about 2.5% to 3.8% of the grain's weight. Most of the oil is polyunsaturated fat: per 100 g, US Department of Agriculture data list 61.7 g of polyunsaturated fat (mostly linoleic acid), 18.8 g of saturated fat and 15.1 g of monounsaturated fat, along with 149 mg of alpha-tocopherol, one of the forms of vitamin E. The oil also carries smaller amounts of plant sterols, carotenoids and policosanols. Laboratory studies show that how the oil is extracted changes the yield more than the fatty acids, while refining at high temperatures lowers the tocopherols.

In short:

• Where it comes from: the germ of the wheat grain, a by-product of flour milling; the germ is 10% to 15% lipids
• Fatty acids: linoleic acid makes up more than half of the oil, followed by palmitic and oleic acid
• Vitamin E: alpha-, beta- and gamma-tocopherol; 149 mg of alpha-tocopherol per 100 g in USDA data
• Other minor compounds: plant sterols (mainly β-sitosterol), carotenoids and policosanols such as octacosanol
• Processing: the extraction method changes the oil yield; high-temperature refining lowers tocopherols
• Thai RDI: none for wheat germ oil; vitamin E 9 mg α-TE, total fat 65 g
• Wheat: wheat is a major food allergen; people with a wheat allergy should ask a doctor first

This article explains what wheat germ oil is made of and how processing changes it. It does not discuss what it does in the body. For how wheat germ oil compares with other oils and nuts for vitamin E, see Which foods are high in vitamin E, and how much?, and for a similar oil from rice, see What is rice bran oil, and what does it contain?

What is wheat germ oil?

A wheat grain has three main parts: the outer bran, the small germ (the embryo, which would grow into a new plant) and the large starchy inside, the endosperm. White flour is made mostly from the endosperm, so the bran and germ are separated during milling.

How big is the germ, and what is in it?

A 2012 review by Brandolini and Hidalgo of Italy's agricultural research council (CRA) describes the wheat germ (the embryonic axis and scutellum) as about 2.5% to 3.8% of total seed weight and an important by-product of the flour milling industry.

The review notes that the oil is rich in triglycerides (57% of total lipids), but also contains sterols, mono- and diglycerides, phospholipids and glycolipids.

How is the oil taken out of the germ?

There are two traditional routes: pressing the germ mechanically, or dissolving the oil out with a solvent such as hexane. The 2012 review reports that pressing recovers about 50% of the lipids and solvent extraction about 90%. A newer method uses supercritical carbon dioxide (carbon dioxide held under high pressure so that it behaves like a solvent).

The figures come from different germ samples and laboratories, so they are best read as a range. The Cagliari researchers found that the fatty acid and alpha-tocopherol composition of the oil was not remarkably affected by either the pressure or the extraction method.

Why is the germ treated before extraction?

The Jiangnan University researchers describe wheat germ as rich in linoleic acid and in lipoxygenase, an enzyme, which makes it prone to enzyme-induced oxidation. In their study, the germ was first heated in a microwave (600 W for 3 minutes) to inactivate its enzymes before the oil was extracted.

What fatty acids are in wheat germ oil?

Wheat germ oil is built mainly from linoleic acid (an omega-6 polyunsaturated fatty acid with 18 carbons and two double bonds, written 18:2), palmitic acid (a saturated fatty acid, 16:0), oleic acid (a monounsaturated fatty acid, 18:1) and alpha-linolenic acid (an omega-3 polyunsaturated fatty acid, 18:3).

Fatty acids per 100 g and as a share of the oil

The two columns use different units and different samples, so they are not expected to match exactly. The Jiangnan study found no significant difference in fatty acid composition between oil extracted with hexane, subcritical butane or supercritical carbon dioxide; unsaturated fatty acids made up about 80% of the total. The Indian study found 61.2% polyunsaturated fatty acids in its wheat germ oil.

How much vitamin E is in wheat germ oil?

Vitamin E is the name for a group of fat-soluble compounds. The US Office of Dietary Supplements (ODS) lists eight natural forms: alpha-, beta-, gamma- and delta-tocopherol, and the four matching tocotrienols.

Alpha-tocopherol in food tables

FoodData Central lists 149 mg of alpha-tocopherol per 100 g of wheat germ oil. A tablespoon weighs 13.6 g, and the ODS gives 20.3 mg of alpha-tocopherol in 1 tablespoon. The Thai Reference Daily Intake (Thai RDI) for vitamin E is 9 mg α-TE a day.

Tocopherol forms measured in studies

Studies report the total tocopherols in wheat germ oil in different units. The Jiangnan University study measured each form in its crude oil:

The Indian study reported 273 mg of tocopherols per 100 g of wheat germ oil, compared with 190 mg in wheat bran oil. The two studies used different germ samples and methods, and the 2012 review gives a range of 300 to 740 mg of tocopherols per kg of the germ itself.

A historical note

Alpha-tocopherol was first isolated from wheat germ oil. Herbert Evans, Oliver Emerson and Gladys Emerson reported the isolation in 1936, in a paper titled "The isolation from wheat germ oil of an alcohol, alpha-tocopherol, having the properties of vitamin E". For how natural and synthetic forms of vitamin E differ in structure, see Natural and synthetic vitamin E: how do they differ?

What else does wheat germ oil contain?

Plant sterols

FoodData Central lists 553 mg of phytosterols per 100 g of wheat germ oil. The Jiangnan University study measured 23,270 mg of phytosterols per kg of crude oil, of which β-sitosterol was 19,420 mg, campesterol 2,090 mg and stigmasterol 1,760 mg.

Carotenoids and steryl ferulates

The Indian study found 12.23 mg of carotenoids per 100 g of wheat germ oil, against 2.21 mg in wheat bran oil. It also found steryl ferulates (plant sterols joined to ferulic acid, the same family of compounds as γ-oryzanol in rice bran), but at an eight-fold higher level in wheat bran oil than in wheat germ oil.

Policosanols and octacosanol

Policosanols are a mixture of long-chain alcohols. Researchers at Oklahoma State University define them as aliphatic primary alcohols with 20 to 36 carbons that are constituents of plant waxes. Octacosanol, the policosanol with 28 carbons, has the formula C28H58O and a molecular weight of 410.8.

The 2005 Oklahoma study analysed grain fractions of 31 wheat varieties grown under the same conditions in Oklahoma. Tetracosanol (C24), hexacosanol (C26) and octacosanol (C28) were the main policosanols in all varieties, wheat bran held more policosanol than the germ, shorts or flour, and the varieties differed significantly in content and composition.

Other values in food tables

How does refining change wheat germ oil?

Crude oil is usually refined to remove free fatty acids, colour and odour. Each step can change the minor compounds.

Bleaching

In the Jiangnan University study, crude wheat germ oil was bleached with 3% activated clay at 90 °C for 30 minutes. Polyphenols fell by 17.79% (from 189.09 to 155.45 mg per kg) and total phytosterols by 4.99%, while tocopherols showed no significant difference.

Removing free fatty acids by molecular distillation

The study then removed free fatty acids by molecular distillation, a high-vacuum distillation, at temperatures from 110 °C to 210 °C. The acid value fell as the temperature rose, and so did the tocopherols and phytosterols.

Source: Li et al. 2016. The authors chose 150 °C as the appropriate condition, with a deacidification efficiency of 77.78% and higher retention of tocopherols, polyphenols and phytosterols than at higher temperatures. The study used germ from one flour company in Hebei, China, so the figures describe that material and that equipment.

Is there a recommended daily amount?

Wheat germ oil is a food, not a nutrient with a Thai Reference Daily Intake (Thai RDI), so there is no recommended daily amount for it in Thailand. Its fat counts towards total fat, for which the Thai RDI is 65 g a day from all foods, and its vitamin E towards the Thai RDI for vitamin E of 9 mg α-TE a day. For the other Thai reference amounts, see What are the Thai daily reference amounts for each nutrient?

Upper limit for vitamin E

The ODS reports that the US Food and Nutrition Board set a tolerable upper intake level for adults of 1,000 mg a day, which applies to all forms of supplemental alpha-tocopherol. This is a US upper limit, not an amount to aim for. For more on upper limits, see Which foods are high in vitamin E, and how much?

Who should be careful with wheat germ oil?

People with a wheat allergy or who avoid gluten

Wheat is one of the nine major food allergens listed by the US Food and Drug Administration (FDA), and the FDA describes gluten as a group of proteins found in certain grains such as wheat, barley and rye. FoodData Central lists 0.0 g of protein per 100 g of wheat germ oil, but a composition table does not show whether a particular product carries traces of wheat protein. People with a wheat allergy, or who have been told to avoid gluten, should ask a doctor before using it.

People who take regular medication

The ODS notes that large amounts of vitamin E from supplements can interact with some medicines. If you take medication regularly, tell your doctor or pharmacist about any oils or supplements you use.

Who should talk to a doctor or pharmacist?

If you are pregnant or breastfeeding, or take medication regularly, talk to a doctor or pharmacist before taking dietary supplements.

Dietary supplements are not intended to prevent, treat or cure any disease.