Tomatoes: GM, Aroma And Tradition

For our frugal parents in the late 1960’s, pressure cookers and mason jars were not an option. In fact, since our tomato-dominated gardens couldn’t provide the needed volume, our extended family drove to farms to pick more tomatoes, often overfilling allotted baskets.

Then back home, not for ecological reasons but strictly to lower costs, any glass container in sight was recycled, filled with crushed tomatoes and topped with a basil leaf. Jars and bottles were placed in big oil drums, and fires were lit in the fields behind our suburban homes so we could preserve sauce for the long, upcoming winter.

When we carry out traditions, we are under the illusion that we are repeating acts dating back to the dawn of our culture. But a few years later, as an adolescent, a plaque at Montreal’s Botanical Gardens made me aware that tomatoes are not indigenous to the Old World, let alone Italy. Pasta can be traced to the Roman Empire or at least to Marco Polo, but it was eaten without tomato sauce.

Even after tomatoes were brought in from South America or Mexico (there are two competing hypotheses with not enough evidence to declare a winner) they were assumed to be poisonous because of their similarities to mandrake and belladonna. Finally, at some point between the 1600’s and 1700’s, tomatoes were used for culinary purposes in southern Europe, but the custom did not become widespread until the 1860’s when they were first mass-produced and canning also came into practice.

When it comes to classifying the tomato, many have experienced confusion, regardless of their knowledge of botany. Aside from the Nix versus Hedden issue, people forget or ignore that the seeded berry grows from a flower; they persist in calling it a vegetable because it is not as sweet as a pear or a cantaloupe, and it’s not tossed into a fruit salad. The same applies to other fruits such as peppers, cucumbers and squash. But for a long time, botanists incorrectly classified the domestic tomato as Lycopersicon esculentum, even though Linnaeus in 1753 along with prior taxonomists realized merely from morphological features that it belonged to the same genus as that of wild tomatoes and potatoes. The current classification of Solanum lycoserpicum is based on comparative chloroplast DNA analyses and other molecular studies.

Constant artificial selection, the first form of genetic modification of tomatoes, probably took place in Mexico and Western South America, where the tomato was first domesticated, and it continued later and more intensely in Europe. One of the many resulting changes involved flower structure. The female part, the stigma, has become less protruding and, in the case of commercial varieties, completely surrounded by the fused anthers. This has increased fruit yield, but by preventing cross-pollination, it has reduced genetic variation.

For a while, only the odd spontaneous mutation would cause change. Then in the 1990’s transgenic tomatoes appeared and some failed even before the EU ban of GM foods came into effect. The single-gene approach had been oversimplistic. The Flavr Savr tomato was given a gene that interfered with the production of an enzyme that would normally soften the fruit. The shelf life was indeed extended, but the firmness was not really improved, and the GM fruit could not be harvested when ripe.

Tomato researchers realized that the genetics of a quantitative trait is hard to investigate. The effect of one gene is small and often influenced by environment or by the interaction with other genes. Many tomato traits are genetically controlled by a combined action of quantitative trait loci(QTLs) with favorable allelic genes found in wild species grown in Ecuador, Peru, Chile and even in the Galapagos.

Having spent many hours of my youth picking tomatoes, I’ve always been fascinated by the aroma of tomatoes and by the smell exuded by stems alone. Here are some examples of volatiles found in fresh tomatoes, which some have been investigating probably with the hope of accentuating aroma through genetic modification.

in ppb(parts per billion= mg per 1000 L)`
Human threshold in ppb Other notes  Structure
 cis-3-hexenal  12000  0.25 fresh green aroma; increases  in conc.after tissue disruption  
 b-ionone  4  0.007  
 hexanal  3100  4.5 suppressed by alcohol in tomato; increases after tissue disruption  
 b-damascenone  1  0.002  
 1-penten-3-one  520  1.0 increases after tissue disruption  
 cis-3-hexenol  150  70.0  
 6-methyl-5-hepten-2-one  130  50.0 fruity aroma  

Annually 100 million metric tons of tomatoes are produced worldwide. The leading consumers are Mediterranean countries with 60-100 kg eaten per capita per year. The combination of poverty and lower popularity of the tomato elsewhere in the world creates an overall global annual consumption of only 14 kg/cap/y. The leading producers are China, US, India, Turkey, Egypt, Italy and Spain. Ironically, Italy has become China’s largest customer for the type of tomato used to make tomato paste. There has been even fraudulently labeled “Made in Italy” tomato paste.

Paste, which has a lower water content than fresh tomatoes, is understandably more concentrated in vitamins A, C and the reddish compound lycopene. In test tube studies, lycopene is the best antioxidant among carotenoids. But the same was said of anthocyanins, and then evidence for the in vivo effect turned out to be scant. With lycopene, however, some supportive epidemiological studies have also been done. While the Mayo Clinic maintains that the cancer-preventive action of lycopene is still controversial, many researchers nevertheless believe that increasing the content of lycopenes and other phytochemicals is a worthwhile pursuit, but that it won’t be successful without an interdisciplinary approach.

** in tomato photo: my daughter among her grandmother’s tomatoes, prior to some heavy-duty sauce making.


Genetic Improvement of Solanaceous Crops
Autar K. Mattoo. Maharaj K. Razdan

First Fruit: The Creation of the Flavr Savr Tomato and the Birth of Biotech Foods
Belinda Martineau

The Chemistry of Fresh Tomato Flavor
TURKEY Turk J Agric For25 (2001) 149-155

Volume 29, Number 3 (2010), 553-568, DOI: 10.1007/s10555-010-9246-z

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