Anything that can dissolve in oils can be present in vegetable oil. In a diverse society, the most interesting are sterols, thanks to which some oils are medicinal, such as shea butter and pumpkin seeds. This group also includes the star of vegetable oils, black cumin, whose action is based on essential oil dissolved in triglycerides.
Long chain alcohols
Long-chain alcohols (ten or more carbon atoms) are present in smaller quantities in vegetable oils. These are often fatty acid analogs, such as tetracosanol (14 carbon atoms) or hexacosanol (16 carbon atoms). Other types of alcohols are often diterpene alcohols, which are formed in the synthesis of terpenes. In olive oil, for example, these are geranyl-geraniol and phytol. Although they certainly contribute to taste, these alcohols are likely to have a marginal effect on the human body.
Waxes are esters of long-chain alcohols and fatty acids. In the plant, waxes protect against drying out and are a barrier to pathogenic microorganisms. Waxes can give vegetable oils turbidity, and make oils solid at lower temperatures. They are not considered to contribute to the action of vegetable oils by oral administration and nutrition, but they can have certain effects in cosmetics since waxes protect skin from drying out. However, there is relatively little wax in vegetable oils. Virgin olive oil contains less than 250mg/kg . Waxes serve to control the quality of vegetable oils. For example, the wax content can be used to identify virgin olive oil forged with olive pomace oil, since olive pomace oil usually contains more than 350mg/kg of waxes.
Sterols are one of the most important compounds of the unsaponifiable fraction of vegetable oils that significantly contribute to the action of vegetable oils. Sterols differ in the number of carbon atoms and the number of hydroxide groups, and the sterols themselves can still be esterified (bound with a fatty acid), bound with sugar or other substances.
There are four main groups of sterols described in more review articles :
- free alcohols
- fatty acid esters
- sterile glycosides
- acylated sterile glycosides
- sterol esters with hydroxycinnamic acid
One of the best known phytosterols is β-sitosterol, widely present in plants. In the following figure you can see its structure, and its derivatives belonging to these listed classes of compounds.
Phytosterols have a number of beneficial effects on the body. In cosmetics, they prevent drying and soften the skin (emollient action), and phytosterols also have an approved health claim to help lower cholesterol. Therefore, sterols and the fraction of vegetable oils isolated from the unsaponifiable fraction are used as raw materials in cosmetics, herbal medicines and dietary supplements.
Sterols are also of great importance in quality control of vegetable oils and they are used to detect possible forgeries. The standard of the European Pharmacopoeia 07/2011: 0518 prescribes that virgin olive oil may contain a maximum of 0.5% cholesterol, 4.0% campesterol and 0.5% Δ7-stigmasterol in total sterols, while the total content of Δ5,23-stigmastenediol, chlerosterol, β-sitotsterol, sitostanol, Δ5-avenasterol and Δ5 , 24-stigmastenediol must be at least 93%.
Volatile compounds and essential oils
There are numerous volatile compounds in vegetable oils that contribute exceptionally to the olfactory quality of vegetable oil, smell and taste. Hundreds of volatile compounds have been identified in vegetable oils. So Olias et al. proved that green-fresh aroma in olive oil is given by the compounds hexanal, (E) -2-hexenal, (Z) -3-hexenal, hexan-1-ol, (Z) -3-hexen-1-ol, hexyl acetate and (Z) -3-hexenyl acetate. Aroma of sweet and bitter almonds, plum, apricot and peach oils is produced by a group of cyanogenetic heteroside compounds that release small amounts of cyanide, a characteristic “almond” or “marzipan” odour.
Very rarely volatile compounds are the main group of active compounds. A very famous exception is the black cumin vegetable oil, which owes its biological effect mainly to the essential oil present in black cumin, i.e. the compound thymoquinone, which gives both the characteristic smell and taste of the oil itself.