Growing Flavorful
Tomatoes
There's a lot of science behind the observation that home-grown
tomatoes taste better than store-bought ones.
Next time you enjoy a great-tasting home-grown tomato, consider not
only how wonderful the flavor is, but also how wonderful and amazing it
is that such a small, common fruit houses incredibly complex processes
to produce that flavor.
It's not very hard to taste a tomato and decide whether you like or
dislike the flavor. But what do you really taste? Tomato flavor is a
combination of two major factors and one minor factor. From there,
things get complicated quickly.
The two big players in tomato flavor are sugars and acids. They are
considered to be major factors in flavor because they occur in the
largest quantity.
Fructose and glucose are the two primary sugars produced in the tomato.
Obviously, sugars are the source of the tomato's sweetness. The acids
in the tomato are mainly citric and malic acids. These are the sources
of the tart flavors.
Looking at the possible combinations of sugar and acid levels in
tomatoes, researchers have been able to make some generalizations. Tomatoes with high sugar and high
acid levels are generally considered to have 'good flavor.'
People tend to categorize tomatoes with low sugar and low acid levels
as 'bland.'
A tomato with high sugar but low acid content would most likely be
called 'sweet,' and one with low sugar but high acid content would be
considered 'tart' by most.
The minor factor in flavor is volatile compounds. These occur in minute
amounts, but researchers have found that they are the factor that
contributes most to what we label as 'tomato' flavor.
Volatiles are the key factor that helps us distinguish flavor
differences among varieties with similar sugar and acid content.
The tongue cannot detect these volatile compounds. They are picked up
by the olfactory nerve in the nose, otherwise known as the sense of
smell.
We usually forget that the sense of smell contributes to tasting the
flavor of foods until we are congested and can't smell anything. Then
it seems like many things taste more bland than usual. This is because
our olfactory nerve cannot detect the volatiles in the food we're
eating.
Over 400 different volatile compounds in the tomato have been
quantified by researchers. Of these, only 30 occur in quantities
greater than one part per billion. Only 16 of these compounds have been
associated with significant contribution to tomato flavor.
How does all this relate to the
difference in flavor between home-grown and artificially ripened
tomatoes? The different conditions in which each group is
grown have significant effects on the levels of sugar, acid, and
volatile compounds in the tomatoes produced.
When breeding or choosing a commercial variety of tomato to produce,
flavor is not necessarily the first consideration. Generally speaking,
traits like disease and pest resistance usually rank higher in
importance. Also, a commercial producer must consider how well a
variety can survive harvesting and shipping to market.
This is one reason why commercial
tomatoes are typically picked very under-ripe, at a stage called
'mature green,' meaning in another 24 hours or so it will
show some pink coloring and be at the 'breaker' stage."
Tomatoes that are still green will store a lot longer, and travel
better than ripe tomatoes. Before these tomatoes travel to market, they
are artificially ripened using ethylene gas. Ethylene is naturally
produced by ripening fruits of all kinds. Exposing the mature green
tomatoes to ethylene will trigger the ripening process, so red tomatoes
are delivered to market.
Those tomatoes that were picked at the breaker state do not need the
ethylene to ripen, since they have already begun the process.
Interestingly enough, these breaker tomatoes are the ones sold in
stores as 'vine-ripened.'
Tomatoes destined for processing into canned products are allowed to
ripen fully on the vine, yet must be tough enough to not break during
harvest and transport to the canning facility. They are generally drier
and have thicker skin and flesh than varieties intended for fresh
consumption. They are definitely not the tender juicy home-grown
tomatoes people savor each summer.
Exposure to
sunlight is crucial for sugar production in tomatoes.
Picking mature green or breaker stage tomatoes reduces their time in
the sun, and reduces the levels of sugar in the tomatoes.
Some studies have related the amount of potassium to acid levels in
tomatoes. Fertilizing with greater amounts of potassium resulted in
higher acid content in most varieties.
Research has shown that artificially ripened tomatoes have
significantly lower levels of volatile compounds than home-grown, fully
ripened tomatoes.
The million-dollar question that remains unanswered is how to
artificially induce green tomatoes to produce the volatile compounds.
An even more complex question is identifying the genes that regulate
production of the volatile compounds. The goal is to allow breeders to
select for plants with the best genetic profile for producing these
compounds in developing new varieties.
Farther down the road, the dream of some researchers is to genetically
engineer tomato plants to produce more volatiles by physically
inserting the genes responsible for their production.
Source:
Jennifer Fishburn,
University of Illinois Extension horticulture educator., (217) 782-4617
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