On the supermarket shelves, in the wet market, there are large red tomatoes. They are bright in color and resistant to storage, but consumers have complained that the tomatoes they buy now are not delicious and lack the "tomato flavor" in their memories.
Why isn't this big red tomato delicious?
What is "tomato flavor"?
The "tomato flavor" at the pure taste level is simple to say: it is mainly a combination of organic acids and sugars. Studies believe that the sweetness of tomatoes comes from glucose and fructose, and the sour taste mainly comes from citric acid and malic acid. In addition, amino acids such as glutamate also enhance the taste of tomatoes.
However, sweet and sour is certainly not the whole of "tomato flavor". The "taste" that people experience when eating food is actually a combination of taste, smell and other senses (touch, temperature feeling, etc.).
In the middle, the odor molecules perceived by the sense of smell during the chewing process play a particularly important role. In terms of smell, the chemicals that make up the "tomato flavor" are much more complex. Scientists isolated more than 400 volatile compounds from tomatoes, but only 30 of them reached the detection threshold of smell, including hexenal, β-ionone, hexanal, β-damanone, etc. These molecules are derived from biological enzymes for the hydrolysis of lipids, amino acids, carotenoids and terpenoids.
The aroma of some fruits and vegetables and spices is mainly contributed by one or a few molecules. For example, as long as there is vanillin, it can well restore the vanilla flavor, and as long as there is isoamyl acetate, it can immediately make people feel "this is a banana". But the case with tomatoes is more complicated, and it is not easy to restore the tomato aroma with a simple set of chemical ingredients.
In 1993, Buttery tried to recreate the scent of a ripe tomato with 16 important molecules out of 30 flavor molecules from tomatoes. Unfortunately, the other 14 "less important" molecules seem to be indispensable in the tomato flavor. They have a subtle effect on the aftertones of tomato flavor.
Why has the tomato become tasteless?
When people feel that tomatoes are "insufficient in taste", the problem is mainly in the lack of aromatic substances. The scent molecules of tomatoes enhance the feeling of "sweetness" and create a rich taste. When a tomato loses a specific volatile substance, consumers will also significantly reduce their liking for it.
That is what destroys the aroma of tomatoes, first of all people think of the refrigerator: tomatoes are reduced in fragrance substances when stored at low temperatures. There is some truth to this claim, for example, studies have found that as the refrigeration time increases, the content of aroma components in tomatoes decreases, and the expression of genes associated with this also changes.
That's not all the answer, the more fundamental reason for the tomato flavor is still in the genes. To get this straight, after analyzing nearly 400 varieties, the researchers mapped a flavor-gene map of the tomato, pinpointing genetic changes associated with flavor loss in modern tomato varieties. As a result, the researchers found the root cause of the unpalatability of modern tomatoes: Compared with traditional varieties, the modern varieties have a total of 13 flavor-related volatile ingredients that are significantly lower. Today, when the flavor of the big tomato is eclipsed, cherry tomatoes, which are the older tomato strains, still maintain a relatively sweet flavor.
Two evolutionary stages of tomato fruit enlargement
What makes the taste worse by layers of breeding?
Those modern tomato varieties that "have no tomato flavor" are the result of layers of artificial breeding. It is reasonable to say that selective breeding should make crops more and more in line with people's expectations, so why is its flavor worse than before?
In the past, breeders may have chosen only storable, large, and beautiful-looking tomatoes. The selection of these aspects does not make the tomato taste better, and may even contradict the deliciousness.
For example, there is a gene called SlGLK2, and the common tomato varieties we see in supermarkets carry its mutants. The gene's original role was to promote the production and distribution of chloroplasts in developing fruits, and mutations inactivated the gene. This mutation makes the color of the tomato fruit very uniform, so it is favored by the breeders. At the same time, however, this is detrimental to the production of sugar and aromatic substances.
Moreover, compared with acids and sugars, the content of various flavor volatile substances in the fruit is very small, and the concentration is in the order of 10 ^(-12)] to nanomol [10^(-9)]. Unless highly sensitive detection techniques are invested, it is difficult to achieve selection and quantification. The researchers say that these flavors, which are missing from modern tomato varieties, are not suddenly lost in a single breed, but are the result of gradual accumulation.
How to save tomato flavor?
The researchers hope to restore the flavor of modern tomatoes. They will focus on those aromatic substances. These odorous substances all work at very low concentrations, and a little increase in the content of the fruit may bring about a great improvement in flavor, which is more feasible than increasing the sugar content. Moreover, aromatic substances will also greatly affect people's perception of sweetness, which can enhance the sweet feeling without shrinking the size of the fruit.
Tomato varieties that have lost their taste will also be expected to return to their old sweetness.