Plant oils as a source of vitamin E in the human diet

Petra Libertova

Bachelor's thesis

Abstract:

According to the classical concept, vitamin E includes four tocopherols (α-, β-, γ-, and δ-tocopherol) and four tocotrienols (α-, β-, γ-, and δ-tocotrienol), collectively referred to as tocochromanols or tocols. This group of amphipathic lipid-soluble molecules generally consists of a polar part derived from tyrosine and a hydrophobic polyprenyl side chain derived from the isoprenoid structure. Tocochromanols are synthesized by photosynthetic organisms, therefore plant products provide the only natural dietary sources of these substances. The primary site of accumulation of tocochromanols is plastids, where their biosynthesis takes place. The formation of the polar chromanol ring from homogentisate is mediated via shikimate pathway, whereas the methylerytrithol phosphate pathway provides the lipophilic prenyl tail from geranylgeranyl diphosphate and phytyl diphosphate for the synthesis of tocotrienols and tocopherols, respectively. The key role of tocochromanols in plants is their complex system of protective mechanisms that together protect light-harvesting tissues from photooxidative damage. They are particularly important during intense light stress or in the absence or failure of other protective mechanisms. Tocochromanols, especially α-tocopherol, effectively neutralize singlet oxygen molecules. In the human body vitamin E plays a significant role as an antioxidant. The main principle of the antioxidant action of tocopherols and tocotrienols is to break the radical chain reaction by quenching peroxyl radicals. Vitamin E may also be involved in the regulation of gene expression and the maintenance of physiological functions of the immune system, such as the stimulation of phagocytic function, which is important in defending the body against infectious diseases. Since all the natural forms of vitamin E are of plant origin, vegetable oils are the most important and concentrated dietary source of vitamin E for humans. Many oilseeds are currently being used as functional foods, primarily because oils derived from the seeds of field crops are often high in unsaturated fatty acids. Coconut, cottonseed, olive, palm, peanut, rapeseed/canola, soybean, and sunflower oils are the most common plant oils. Usually, α -tocopherol (102-575 mg/kg) and γ-tocopherol (15 -592 mg/kg) are the most occurring tocopherols among these oils from their total tocopherol content. However, non-traditional oils that could diversify our diet are poppy seed oil and soybean oil, due to their content of β- and δ-tocopherol, which are not commonly abundant. Poppy seed oil contains β-tocopherol roughly in scale from 261 to 268 mg/kg and δ-tocopherol in soybean oil is from 182 to 185 mg/kg of its total tocopherol content. Furthermore, palm fruit is the richest source of tocotrienols among all plant oils. Tocotrienols make up almost 70% of vitamin E in palm oil, with the remaining 30% being tocopherols. However, in order to reasonably determine the suitability of including different plant oils in the human diet, it will be necessary to conduct scientific research to evaluate the influence of genetic as well as environmental factors on the tocol content and profile of different oil corps.

Keywords

vitamin E, tocopherols, tocotrienols, lipophilic antioxidants, rapeseed oil, poppy seed oil, sunflower seed oil

Language used: English

Date on which the thesis was submitted / produced: 1. 5. 2024

Thesis defence

• Date of defence: 28. 5. 2024
• Supervisor: Ing. Barbora Burešová, Ph.D.
• Reader: Matěj Satranský, Ph.D.

Czech University of Life Sciences Prague

Faculty of Agrobiology, Food and Natural Resources

Bachelor programme:
Food Quality and Processing of Agricultural Products