Why Does a Tomato Turn Red?

A tomato doesn't begin its life looking much like the one we slice for a sandwich or simmer into sauce.

It starts out small, green and firm.

Then something remarkable happens.

As the tomato matures, its texture changes. Its flavor changes. Its aroma changes. And, in many familiar tomato varieties, green gradually gives way to red.

That color change is something we see so often that it's easy to overlook the science behind it.

But a ripening tomato is going through an enormous transformation - and one of the stars of that transformation is lycopene.

Why Is an Unripe Tomato Green?

Young tomatoes contain chlorophyll, the green pigment plants use to capture light energy for photosynthesis.

That's why an immature tomato blends so nicely with the leaves and stems around it.

As the tomato reaches maturity and begins to ripen, that changes.

Chlorophyll starts breaking down, so the green color begins to disappear. At the same time, the tomato's production and accumulation of other pigments increases.

In red tomatoes, one of the most important of those pigments is lycopene.

The result is something we can watch with our own eyes:

Green becomes lighter.

Hints of yellow, orange or pink may appear.

Red begins to spread.

Eventually, we have a ripe red tomato.

Meet Lycopene

Lycopene belongs to the large family of plant compounds called carotenoids.

It's the pigment responsible for much of the red color in ripe tomatoes. It's also found in foods such as watermelon, pink grapefruit and guava.

But tomatoes are particularly well known as a dietary source of lycopene.

And here's the interesting part:

A green tomato doesn't simply have red lycopene hiding underneath its chlorophyll, waiting for the green color to disappear.

As many red tomato varieties ripen, lycopene actually accumulates in the fruit.

The tomato isn't merely revealing its red color.

It's changing chemically as it matures.

Ripening Is About Much More Than Color

Anyone who has ever bitten into a hard, unripe tomato knows that turning red isn't the only change taking place.

During ripening, enzymes begin changing the tomato's cell walls, helping the fruit soften.

Starches and sugars change.

Acids change.

Hundreds of compounds involved in aroma and flavor develop and shift.

That's why a ripe tomato doesn't simply look different from a green one.

It feels different.

It smells different.

And it certainly tastes different.

Ripening is a coordinated biological process that transforms the fruit.

Why Would a Plant Do All That?

The tomato plant isn't trying to make a better salad.

The changes that occur during ripening have an important purpose for the plant.

A tomato is botanically a fruit, and inside that fruit are seeds.

When the seeds are developing, a hard green fruit isn't particularly appealing to many animals.

Once the seeds are mature, however, everything changes.

The fruit softens.

Its aroma develops.

Its flavor changes.

And its color becomes much easier to notice.

An animal eats the ripe fruit and may carry or deposit the seeds somewhere away from the parent plant.

From the plant's point of view, ripening can help with the next generation.

What Does Lycopene Do for Us?

Lycopene has attracted a great deal of scientific attention because of its antioxidant properties and its possible role in human health.

Researchers have studied lycopene in connection with cardiovascular health, including its relationship with blood vessels, inflammation, oxidative processes and other factors involved in maintaining a healthy cardiovascular system.

Research continues, and eating tomatoes isn't a treatment for heart disease.

But tomatoes bring something useful to the conversation that a lycopene supplement alone cannot: they're whole foods containing fiber, vitamins, minerals and numerous other phytochemicals alongside lycopene.

Here's Something Surprising About Cooked Tomatoes

We often hear that fresh vegetables are always nutritionally superior to cooked ones.

Tomatoes are a wonderful example of why nutrition isn't quite that simple.

Cooking breaks down some of the structures in tomato tissue. When tomatoes are cooked and processed, lycopene can become easier for our bodies to absorb.

Lycopene is also fat-soluble, so eating tomatoes with some dietary fat can help with its absorption.

That makes foods such as cooked tomato sauce with a little olive oil interesting from a nutrition standpoint.

Cooking can reduce certain heat-sensitive nutrients while making other compounds more available to us.

“Raw is better” and “cooked is better” are both too simple.

Sometimes they're simply different.

Look at a Tomato a Little Differently

The next time you see tomatoes at different stages of ripeness, stop and look at them.

A green tomato and a red tomato aren't merely two versions of the same fruit with different paint jobs.

One is still moving through the ripening process.

Pigments are changing. Cell walls are changing. Flavor and aroma compounds are changing. The chemistry inside the fruit is changing.

And as that familiar red color develops, lycopene is accumulating.

It's a beautiful example of something plants do every day without us giving it much thought.

A tomato doesn't simply turn red.

It ripens.

Lyla & the Big-Hearted Tomato Interactive Flipbook for computers, tablets and smartphones.