New vitamin E form extracted from kiwifruit: Scientists

Writing in the journal Food Chemistry​, researchers from the two Neapolitan universities report the identification and characterisation of a compound called delta-tocomonoenol, which is an analogue of tocopherol.

There are eight forms of vitamin E: four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta). Alpha-tocopherol is the main source found in supplements and in the European diet, while gamma-tocopherol is the most common form in the American diet.

Studies of the tocomonoenol’s radical-scavenging and antioxidant capacities “showed its involvement in the total antioxidant activity generally attributed to this fruit”​, wrote the researchers, led by Antonio Fiorentino from the Universita degli Studi di Napoli.

The unique kiwi​

Commenting independently on the study, Dr Tony McGhie, research scientist from the New Zealand Institute for Plant and Food Research (formerly HortResearch) told NutraIngredients.com: “Finding a further source of vitamin E activity is important because fruit are generally not good sources of vitamin E with the exception of avocado and kiwifruit (1.5-2 mg/100g). ​

“Also, the role of the various forms of vitamin E is the subject of much debate and discussion, so adding a new compound to the vitamin E category, perhaps unique to kiwi, may confer a unique biological property for kiwifruit, and be something we might want to exploit.”​

Study details​

The Neapolitan researchers dried the peels of kiwi fruit at 45 Celsius overnight. Hexane was used as the extraction solvent, and the researchers identified three vitamin E compounds: alpha-tocopherol, delta-tocopherol, and “a new vitamin E, named delta-tocomonoenol”​.

Various analytical techniques were used to elucidate the structure of the compound as 2,8-dimethyl-2-(4,8,12-trimethyltridec-11-enyl)chroman-6-ol, and it was predominantly present in the peel. On the other hand, alpha-tocopherol was found in both the peel and pulp of the fruit.

Results from the DPPH (2,2’-diphenyl-1-picrylhydrazyl radical) assay showed that the delta-tocomonoenol and delta-tocopherol had similar radical scavenging, of about 24 per cent.

Measures of the compounds ability to prevent the auto-oxidation of lipid substrates, measured by the formation of conjugated diene hydroperoxides, showed that alpha-tocopherol performed the best (33 per cent inhibition), followed by delta-tocomonoenol (27 per cent), and the delta-tocopherol (25.5 per cent).

Results from the TBARS (thiobarbituric acid reactive species) assay, a measure of lipid oxidation, showed the same pattern, alpha-tocopherol performed the best (53 per cent inhibition), followed by delta-tocomonoenol (47 per cent), and the delta-tocopherol (43 per cent).

Who eats the skin?​

Dr McGhie added a note of caution concerning the research, saying: “Vitamin E is often measured as specific compounds and often only a-tocopherol is measured. Including the delta-tocomonoenol form increases the concentration of vitamin E that can be reported for kiwifruit - further support of the nutrient-dense claim for kiwifruit. ​

“Unfortunately much of the delta-tocomonoenol is in the skin and so not relevant to green or gold, but could be very relevant when skin is consumed.”​

Source: Food Chemistry​ Volume 115, Issue 1, Pages 187-192"delta-Tocomonoenol: A new vitamin E from kiwi (Actinidia chinensis) fruits"​ Authors: Antonio Fiorentino, C. Mastellone, B. D’Abrosca, S. Pacifico, M. Scognamiglio, G. Cefarelli, R. Caputo, P. Monaco