Tomatoes with enhanced antioxidant properties

18 November 2017

In a study on the nutritional value of tomatoes, Professor Chye Mee-len (Croucher Senior Research Fellowship 2007) has used genetic modification to increase both vitamin E and vitamin A content.

Chye and her colleagues identified a new strategy to simultaneously enhance health-promoting vitamin E by 6-fold and double both provitamin A and lycopene contents in tomatoes, to significantly boost antioxidant properties.

Her research group manipulated the plant isoprenoid pathway through the utilisation of a variant of 3-hydroxy-3-methylglutaryl-coenzyme A synthase (HMGS). The overexpression of HMGS in tomatoes increased not only phytosterols, squalene, provitamin A and lycopene, but also vitamin E (α-tocopherol) by 494%.

The HMGS DNA used in these experiments originated from a food crop, Brassica juncea (Indian mustard), that yields edible leaves, stems and seeds, the latter used in vegetable oil production. Earlier, this research group reported that the recombinant HMGS variant S359A (in which amino acid residue “serine” at position 359 was switched to “alanine”) exhibits 10-fold higher enzyme activity. The introduction of S359A in the model plant Arabidopsis increased phytosterol content.

Carotenoid extracts from S359A tomato fruits (right) show a deeper colour and contain more carotenoids (provitamin A and lycopene) than the control (left). S359A-1 and S359A-2 represent two independent S359A tomato lines that give consistent results.

Now, the research group has introduced the S359A into tomatoes, a crop plant. Although there were no differences in the appearance and size of the transformed tomato fruits, total carotenoids including provitamin A and lycopene increased drastically by 169% and 111%, respectively, as observed by a deeper colour of carotenoid extracts in S359A tomatoes over the control (Figure 1). Furthermore, these carotenoid extracts exhibited 89.5-96.5% higher antioxidant activity than the control (Figure 2). Besides carotenoids, the transformed tomatoes displayed elevations in vitamin E (α-tocopherol, 494%), squalene (210%), and phytosterols (94%). These observations were attributed to the increased expression of genes in the isoprenoid pathway.

Chye said, “Increasing health-promoting components in crops is an important research area on the use of plant biotechnology for a sustainable future. The accumulation of the healthy components in food crops would provide added-value to fruits and vegetables in the human diet, as well as enrich feed for livestock and aquaculture.” 

“Extracts with enriched phytosterols, vitamin E and carotenoids can be used in the production of anti-ageing cream and sun-care lotion. These compounds show excellent anti-inflammatory and antioxidant activity,” added Chye. 

There were no differences in the appearance and size of the transformed tomato fruits.

Professor Chye Mee-len, Wilson and Amelia Wong Professor in Plant Biotechnology at the University of Hong Kong, completed her PhD on a Commonwealth Scholarship at the University of Melbourne and received postdoctoral training in Plant Molecular Biology at the Rockefeller University (New York) and the Institute of Molecular and Cell Biology (Singapore). She joined the University of Hong Kong in 1993 and has been awarded an Edward Clarence Dyason Universitas 21 Fellowship 2004/05, an Outstanding University Researcher Award 2006/07 and a Croucher Senior Research Fellowship 2007/08. She serves on the editorial boards of Planta (Springer), Frontiers in Plant Metabolism & Chemodiversity and Frontiers in Plant Physiology.

To view Prof Chye’s Croucher profile, please click here