Free and Esterified Tocopherols, Tocotrienols and Other Extractable and Non-Extractable Tocochromanol-Related Molecules: Compendium of Knowledge, Future Perspectives and Recommendations for Chromatographic Techniques, Tools, and Approaches Used for Tocochromanol Determination

Free and esterified (bound) tocopherols, tocotrienols and other tocochromanol-related compounds, often referred to “tocols”, are lipophilic antioxidants of great importance for health. For instance, α-tocopherol is the only tocochromanol with vitamin E activity, while tocotrienols have a positive impact on health and are proposed in the prevention and therapy of so-called modern diseases. Tocopherols, tocotrienols and plastochromanol-8 are the most well-known tocochromanols; in turn, knowledge about tocodienols, tocomonoenols, and other rare tocochromanol-related compounds is limited due to several challenges in analytical chemistry and/or low concentration in plant material. The presence of free, esterified, and non-extractable tocochromanols in plant material as well as their biological function, which may be of great scientific, agricultural and medicinal importance, is also poorly studied. Due to the lack of modern protocols as well as equipment and tools, for instance, techniques suitable for the efficient and simultaneous chromatographical separation of major and minor tocochromanols, the topic requires attention and new solutions, and/or standardization, and proper terminology. This review discusses the advantages and disadvantages of different chromatographic techniques, tools and approaches used for the separation and detection of different tocochromanols in plant material and foodstuffs. Sources of tocochromanols and procedures for obtaining different tocochromanol analytical standards are also described. Finally, future challenges are discussed and perspective green techniques for tocochromanol determination are proposed along with best practice recommendations. The present manuscript aims to present key aspects and protocols related to tocochromanol determination, correct identification, and the interpretation of obtained results

Sea buckthorn (Hippophae rhamnoides L.) vegetative parts as an unconventional source of lipophilic antioxidants

The profile of lipophilic antioxidants in different vegetative parts (leaves, shoots, buds and berries) was studied in sea buckthorn (Hippophae rhamnoides L.) male and female plants collected in the end of spring. Five lipophilic compounds, i.e. three tocopherol homologues (α, β and γ), plastochromanol-8 and β-carotene, were identified in each vegetative part of male and female sea buckthorn plants at the following concentrations: 7.25–35.41, 0.21–2.43, 0.41–1.51, 0.19–1.79 and 4.43–24.57 mg/100 g dry weight basis. Additionally, significant amounts of α-tocotrienol (1.99 mg/100 g dry weight basis) were detected in buds. The α-tocopherol and β-carotene were predominant lipophilic antioxidants in each vegetative part, accounting for 78.3–97.0% of identified compounds. The greatest amounts of lipophilic antioxidants were found in leaves, especially of female plants. Nevertheless, apart from leaves, also shoots of plants of both sexes seem to be a good source of α-tocopherol and β-carotene

Rapid Separation of All Four Tocopherol Homologues in Selected Fruit Seeds via Supercritical Fluid Chromatography Using a Solid-Core C18 Column

Tocopherol separations employing the same Kinetex™ C18 column via supercritical fluid chromatography (SFC) and reversed-phase liquid chromatography (RP-LC) were compared. The application of the SFC system with UV diode array detection (DAD) resulted in rapid separation of all four tocopherol homologues with a total analysis time below 2 min. The RP-LC approach could not separate the isomers β and γ. The developed SFC-DAD method was precise, accurate, and most importantly more environmentally friendlier compared to the RP-LC method due to the 125-fold decrease in methanol consumption. The present study illustrated the selectivity differences between LC and SFC and how the C18 column can be used for tocopherol characterization. The optimized SFC method was successfully applied for the tocopherol determination in the seeds of nine different fruit species

Tocopherol and tocotrienol contents in the sea buckthorn berry beverages in Baltic countries: Impact of the cultivar

Introduction. The soft part of the sea buckthorn (Hippophae rhamnoides L.) berry is not only rich in juice but also in oil, a valuable source of tocopherols and tocotrienols (vitamin E). Therefore, sea buckthorn beverages are becoming increasingly popular in the world market, and may be considered as a valuable source of vitamin E in the daily diet. Materials and methods. The contents of tocopherol and tocotrienol homologues in 28 different commercially available sea buckthorn beverages (nectars and juices) from three Baltic countries, and juice samples obtained in lab-scale from 6 cultivars of the berries, were studied via RP-HPLC/FLD and a DPPH assay. Results and discussion. A wide range for the total tocochromanol concentration in both commercially available nectars (0.25 to 26.33 mg L-1) and juices (12.63 to 75.90 mg L-1) of sea buckthorn were noted. The profile of tocopherol (T) homologues in the sea buckthorn beverages was as follows: α-T (85%), β-T (6.2%), γ-T (2.8%) and δ-T (0.6%). Tocotrienol (T3) homologues constituted only a minor part: α-T3 (1.8%), β-T3 (0.3%), γ-T3 (2.4%) and δ-T3 (1.0%). The total tocochromanol content in the sea buckthorn juice prepared in lab-scale from 6 different cultivars was the lowest for cv. Prozrachnaya and the highest for ‘Avgustinka’ (39.52 and 73.08 mg L-1, respectively). A significant correlation (r = 0.968, P <0.00001) between the total content of tocochromanols in the sea buckthorn beverages and scavenging of free radical DPPH was found. Conclusion. Commercially available sea buckthorn berry beverages had a wide range of the tocochromanol content (0.25–75.90 mg L-1). The juices were found to be the richest source of tocochromanols out of all the beverages studied, mainly in the form of α-T (85%). The concentration of tocochromanols in the sea buckthorn beverages was strongly associated with the antioxidant activity of tested samples determined by the DPPH assay

Sterols and squalene in apricot ( Prunus armeniaca

The profile of sterols and squalene content in oils recovered from the kernels of 15 apricot (Prunus armeniaca L.) varieties were investigated. Nine sterols (campesterol, β-sitosterol, Δ5-avenasterol, 24-methylene-cycloartanol, cholesterol, gramisterol, Δ7-stigmasterol, Δ7-avenasterol and citrostadienol) were identified in apricot kernel oils. The β-sitosterol was the predominant sterol in each cultivar and consisted of 76–86% of the total detected sterols. The content of total sterols and squalene were significantly affected by the variety and ranged between 215.7–973.6 and 12.6–43.9 mg/100 g of oil, respectively

Chemical Composition of Seed Oils Recovered from Different Pear (Pyrus communis L.) Cultivars

Lipophilic bioactive compounds in oils recovered from the seeds of eight pear (Pyrus communis L.) cultivars were studied. Oil yield in pear seeds ranged between 16.3 and 31.5 % (w/w) dw. The main fatty acids were palmitic acid (6.13–8.52 %), oleic acid (27.39–38.17 %) and linoleic acid (50.73–63.78 %), all three representing 96–99 % of the total detected fatty acids. The range of total tocochromanols was between 120.5 and 216.1 mg/100 g of oil. Independent of the cultivar, the γ-tocopherol was the main tocochromanol and constituted approximately 88 %. The contents of the carotenoids and squalene were between 0.69–2.99 and 25.5–40.8 mg/100 g of oil, respectively. The β-sitosterol constituted 83.4–87.6 % of total sterols contents, which ranged between 276.4 and 600.1 mg/100 g of oil. Three significant correlations were found between oil yield and total contents of sterols (r = −0.893), tocochromanols (r = −0.955) and carotenoids (r = −0.685) in pear seed oils