Untitled Document
There’s a lot of science behind the observation
that homegrown tomatoes taste better than store-bought ones. “It’s not very hard to taste a tomato and
decide whether you like or dislike the flavor,” says Jennifer Schultz
Nelson, a horticulture educator with the University of Illinois Extension,
“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, which occur in the largest quantities.
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, mainly citric and malic
acids, are the source of the tart flavor. “Looking at the possible combinations of sugar
and acid levels in tomatoes, researchers have been able to make some
generalizations,” she says. “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
greatest contributor to what we label “tomato” flavor, she
adds. The tongue cannot detect these volatile compounds;
instead, they are picked up by the olfactory nerve in the nose. “We
usually forget that the sense of smell contributes to tasting the flavor of
foods until we are congested and can’t smell anything,” Nelson
says. “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.”
More than 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 contributions to tomato flavor. “How does all this relate to the difference in
flavor between homegrown and artificially ripened tomatoes?” she
says. “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.”
Flavor is not necessarily the first consideration for
commercial growers. Generally speaking, such traits as disease and pest
resistance rank higher in importance. Also, a commercial producer must
consider how well a variety can survive harvest and shipment to market. “This is one reason why commercial tomatoes are
typically picked very underripe, 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,” Nelson says.
“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 with the use of ethylene gas, which is naturally
produced by ripening fruits of all kinds. Exposing the mature green
tomatoes to ethylene will trigger the ripening process, permitting the
grower to send red tomatoes to market. Tomatoes picked at the breaker state do not need
ethylene to ripen, because the process has already begun. Curiously, 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 but must be tough enough to not
break during harvest and transport to the canning facility. They are
definitely not the tender, juicy homegrown tomatoes people savor each
summer.
“Exposure to sunlight is crucial for sugar
production in tomatoes,” Nelson says. “Picking mature green or
breaker-stage tomatoes reduces their time in the sun and reduces the levels
of sugar in the tomatoes.”
For more information about the University of Illinois
Extension’s Sangamon-Menard unit, go to
www.extension.uiuc.edu/Sangamon.
This article appears in Jun 21-27, 2007.
