Tomato is one of the most popular and extensively consumed vegetable crops worldwide. There is evidence that regular tomato consumption decreases the incidence of chronic degenerative diseases such as certain types of cancer and cardiovascular diseases.
These observed health effects are due to the presence of different anti-oxidant molecules such as carotenoids; (particularly lycopene, ascorbic acid, vitamin E), and phenol compounds, (particularly flavonoids). Lycopene is the major carotenoid compound in tomatoes, and gives the fruit its red colour.
In 2007 the Heritage Food Crops Research Trust (in conjunction with the New Zealand Tree Crops Association Central Districts Branch and Bristol Plants and Seeds) grew 64 tomato varieties, and had them chemically analysed by Dr Tony McGhie at Hort Research in Palmerston North.
The study was looking to find tomato varieties with high lycopene levels that may be of benefit as a preventative for cancer, and also to determine whether open-pollinated heirloom varieties were superior in levels of these health promoting compounds to modern commercially produced hybrid varieties.
An heirloom variety called Oxheart was found to have the highest levels of lycopene in this study, and had twice the amount of lycopene as Daniella the popular modern hybrid variety tested.
Oxheart is an old, 19th Century tomato variety that originated in Italy. It is a large, smooth, red, heart-shaped, flavoursome tomato with very meaty flesh and few seeds.
Our study confirmed previous overseas findings, with the variety Caro Rich testing with the highest levels of beta-Carotene.
Oxheart and Matt’s Wild Cherry both tested with the highest levels of total carotenoids, followed by Amish Paste and Black Krim.
Baxters Early Bush Cherry was found to have the highest levels of Chlorophyll a and b.
Testing for polyphenolic compounds resulted in Matt’s Wild Cherry scoring substantial levels compared to all other varieties. Matt’s Wild Cherry scored the highest or second highest levels in 5 out of the 8 polyphenolic compounds. Matt’s Wild Cherry is a prolific small sweet cherry tomato that originated in Mexico, where it grows in the wild.
It is an exciting find of this research that Matt’s Wild Cherry scored so highly and consistently with the highest levels of polyphenolics, highest equal (with Oxheart) in total Carotenoids and with high levels of Chlorophyll compounds. With the key anti-cancer compound lycopene, Matt’s Wild Cherry scored the 7th highest levels out of our 64 varieties tested.
Given our growing understanding that individual compounds such as lycopene do not work in isolation, but they work in association with other compounds to produce a synergistic effect, (that may be observed through a reduced level of chronic disease in humans) then Matt’s Wild Cherry is an excellent variety for further research into cancer prevention. To this end we will be growing this variety in 2008 along with Oxheart, to produce sufficient tomatoes of each variety that will be sent to Dr Tony McGhie to be converted to powdered extract and then sent to Dr Francis Raul in Strasbourg for testing against colon cancer cells.
Heirlooms versus Hybrids
The modern commercially produced hybrid Daniella that we used in this study is a popular commercially grown variety in New Zealand and in other places around the world. For instance in Morocco it is regarded as the most popular cultivar for its firmness, high vigour, shelf life, tolerance to salinity and low temperatures.
Of the 16 individual compounds tested for in this study, Daniella ranked in the top 20 in only one of those compounds (ranking 10th for an unknown polyphenolic compound). Hence the heirloom varieties exhibited far superior levels of all the compounds tested for.
We can deduce from this that the consumption of heirloom tomato varieties is likely to be better for human health, and that some of the heirlooms such as Oxheart and Matt’s Wild Cherry may have very superior potential as functional foods to be eaten to reduce the incidence of chronic disease.
We found our 2007 research project to be a very positive one. We especially enjoyed the involvement of local specialist growers Frank and Joy Bristol from Bristol Plants and Seeds. Their expertise, reliability and resources were of great assistance to the project. (Interestingly they were so impressed with the diversity, quality and level of interest shown by the local community in the heirloom cultivars that they grew for this project, that they may concentrate in future on commercially growing heirlooms rather than hybrid varieties).
We also very much appreciated the local community support and funding received for this project from the Pamela Williams Family Trust; the Trident Trust; Pub Charity and the Wanganui South Rotary Club and Community Trust.
Once we received the results of the chemical analysis, (in association with the Whanganui Regional Primary Health’s “Grab a Bite That’s Right” programme), 3,000 plants of the 10 top heirloom varieties were grown for free distribution. These were given away in November 2007 to residents of Wanganui and surrounding areas. There was a tremendous response to this giveaway and we were very encouraged by the enthusiastic gardeners who came for their tomato plants as well as the number of non-gardeners who were willing to have a go at growing them.
Advantage of Heirloom Varieties
All heirloom tomato varieties are “open pollinated” varieties, which means that you can save the seed and grow them in future years. Unlike hybrid tomatoes where seeds do not breed true to type, so that seeds saved may not grow to produce the same tomato, heirloom tomato seeds, because they are normally self pollinated, should grow true to type.
Now with the increased levels of carotenoid and polyphenolic compounds in heirloom cultivars, there is a definite reason to grow these varieties and save their seeds.
As already referred to we intend to grow Matt’s Wild Cherry and Oxheart so that they can be converted to powdered extract and sent to Dr Francis Raul in Strasbourg for testing for their ability to inhibit colon cancer cell proliferation.
We have two further collaborations in place. Dr Nicoletta Pellegrini of the Department of Public Health at the University of Parma and Dr Maria Ercolano of the Department of Soil, Plant and Environmental Sciences at the University of Naples were two of the authors of a paper published in February 2007 titled “Antioxidant Nutritional Quality of Tomato”. Following our communication with them they kindly sent us seeds of their top 5 open pollinated varieties (chosen for lycopene levels), and we will grow these to determine their comparable levels of compounds under New Zealand growing conditions.
We have also entered into a collaboration with a major privately owned heirloom seed bank in the United States. They hold 3,000 tomato cultivars and have donated 50 varieties that they have selected that may be of particular interest for us to grow and test.
Altogether with the Italian and United States selections as well as further New Zealand and overseas varieties collected we have 75 further varieties to grow and test in 2008.
Our research indicates that the lighter colours of tomato skins (green, whites, yellows and oranges) generally result in lower levels of carotenoid and phenolic compounds compared to the pinks, reds, and black coloured tomatoes.
Our future research will tend to focus on these darker coloured varieties.
The benefits of less common varieties of tomatoes are only just beginning to be explored. It is known that the purple colouring in tomatoes comes from the anthocyanins, which also create the colouring in various berries and grapes. Anthocyanins are also known to be antioxidants, which protect the body from cell-damaging “free radicals” and decrease the risk of cardiovascular disease and cancer.
Hence our 2008 study includes varieties such as Purple Russian, Purple Passion, Black Prince and Paul Robeson.
The Health Benefits of Carotenoids, Lycopene and Beta-Carotene
(extract from Antioxidant Nutritional Quality of Tomatoes)
The beneficial effects of tomato consumption are generally attributed to carotenoids, which are able to reduce the risk of certain types of cancer, arteriosclerosis and cataract formation . Two main carotenoids are present in tomato: lycopene, which is the major carotenoid compound (~ 80-90%), giving the red colour to the fruit, and Beta-carotene, which is 7-10% of the total carotenoid content. Lycopene has been shown to have a strong antioxidant activity and to exhibit the highest physical quenching rate consistent with singlet oxygen. On the other hand, Beta-carotene is of special interest due to its provitamin A activity. Tomatoes represent by far the main source of lycopene, whereas many other dietary sources contribute to the daily intake of beta-carotene.
However the tomato fruit is a reservoir of other potentially healthy molecules, such as ascorbic acid, vitamin E and phenolic compounds, particularly flavonoids.
Health Benefits of Phenolic Compounds — Flavonoids
Tomatoes also contain phenolic compounds, which also exhibit a strong antioxidant activity. The antioxidant and free radical-scavenging properties of polyphenol compounds in several plant extracts have been recently reported, suggesting possible protective roles of polyphenol compounds in reducing risk of cardiovascular diseases in humans. Kahkonen et al reported that the total phenolic content of tomatoes is up to 200mg of gallic acid equivalent per 100g (as dried weight). [Gallic acid is a polyphenol used as a reference standard.]
Tomato polyphenols, mainly phenolic acids, are present in free soluble form and in insoluble form when they are bound to a fibre. Moreover, tomato contains flavonoids, in particular rutin and [narigenin chalcone]**. Some papers have pointed out that tomato flavonoids, due to their high antioxidant power and to the significant biological activities, can have a substantial role in the health benefits attributed to tomato consumption .
** The compound identified and tested in our study by Dr Tony McGhie of Hort Research, Palmerston North, New Zealand, is Narigenin Chalcone, expressed as Q-rut equivalents. Dr McGhie advises that many reports find that tomatoes contain narigenin. This is not the case as narigenin is generated by a molecular rearrangement during the extraction process used by many researchers. Narigenin and narigenin chalcone are in fact quite different compounds.