Ever wonder what makes a good tomato taste so great?  Well, so do the plant geneticists trying to produce the “better” tomato.  The amount of sugar has a lot to do with it, but what about that tomato smell?  Our perception of taste is enhanced by how food smells before we put it in our mouths and as we chew it.  The chemicals that produce the tomato aroma are called volatiles.  The food industry assumed that the volatiles that are found in the highest concentrations are the ones that make a tomato a tomato, and these should be the targets of genetic manipulation.  A paper by Tieman et al, which appeared this week in Current Biology, challenges this thinking by systematically investigating what combination of chemicals found naturally in tomatoes makes a delicious tomato.
Mass produced tomatoes are relatively homogenous, so the authors decided to examine the chemical composition of 152 heirloom varieties.  I think it’s worth noting the names of a few of these varieties: Bloody Butcher, Giant Oxheart, Crimson Sprinter, Tasti-Lee, Mr. Stripey, and Mexico Midget.  
Bloody Butcher variety of heirloom tomato. (Credit: Totally Tomatoes)
After figuring out the concentration of chemicals in the tomatoes, the researchers asked consumers to rate the flavor of the tomato varieties.  Surprisingly, a number of generic supermarket tomatoes scored quite high.  There was no simple pattern of chemicals that defined a good tomato.  As you would expect, the flavor profile of a tomato is quite complex, but the authors were able to pull out some new interesting information from their analysis.
1) The volatiles that are the most concentrated in tomatoes do not necessarily correlate with perceived flavor intensity.  In other words, some of the odors that are in the highest concentrations are not associated with flavor intensity.  Take them or leave them, either way the consumer wouldn’t notice.  The authors proved this by testing the flavor of mutant tomatoes that cannot enzymatically produce some of the volatiles that are normally found in high concentrations.  There was no difference in preference between the mutants and normal tomatoes.
2) Some of the volatiles contributed to the perception of sweetness.  In particular, an odor called geranial was positively correlated with sweetness.  To investigate this further, they used a mutant tomato that could not make geranial but still had the same amount of sugars and acids.  Consumers rated these mutants as being less sweet even though the sugar:acid ratio was exactly the same as the normal tomato.  Think about that for a minute… a smell increased the sweetness of a food.  We could replace excess sugars in processed foods with geranial to lower the calories without affecting the overall taste of the food!
So what makes a bloody butcher tomato taste so good?  High levels of geranial and other volatiles that trick your taste perception into thinking you’ve bitten into a slice of heaven.

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