December 23, 1996
WASHINGTON STATE UNIVERSITY Office of News and Information Services
MEDIA CONTACT: Tim Steury 509/335-1378, [email protected]
SKIN DEEP: THE COLOR OF APPLES CAN AFFECT THEIR TASTE
PULLMAN, Wash.--John Fellman hands me another apple, a Rome Beauty, one of the more common varieties in this orchard. "Kind of starchy yet," he says, "but they're getting there."
Fellman, the post-harvest horticulturist at Washington State University, moves to the next tree. "Bet you these are real good right now." He picks a Sungold and hands it to me. "Why don't you throw that one away," he says, nodding at the not-quite-ripe Rome. "You're going to be sick of apples."
So I toss aside the Rome and bite into the Sungold. And then a Berry, an Opalescence, a Grimes Golden. Imperial Red Gala, Golden Russet, Spokane Beauty. Twenty Ounce (so named because a single apple can weigh 20 ounces). Melrose, Winter Banana, Jonathan, Baldwin, Ben Davis, Ganno, King David. Gallia Beauty (a taste I remember distinctly from when I was a kid in Indiana). Jonagold, Macoun, Turley. Wolf River (which Fellman is interested in because it doesn't scald in storage), Jubilee, Braeburn.
It is one of those last gorgeous days of October, and Fellman is leading me through the variety block of WSU's Tukey Orchard, 392 trees of 97 different varieties. The tastes are doing extraordinary things to my nose and taste buds. We are in apple heaven.
The last tree we stop at is stunningly beautiful, a Red Delicious, filled with fruit of the ultimate color sought by Washington orchardists, a deep, almost black, red.
"Try this," says Fellman. I take a bite. Compared to the apples we've been sampling, it tastes like sweet cardboard. It lacks all the complex and interesting depths of the apples behind us. (It lacks, in other words, character.) Once past its glorious exterior, it is one boring piece of fruit.
Funded partly by the Washington State Tree Fruit Research Commission, Fellman worries about things like how to store an apple for ten months without it turning to mush. And how to keep apples tasty, whether fresh out of storage or fresh off the tree.
Taste, particularly in apples, is not a simple thing, says Fellman. Tasting an apple happens in stages. Try this, with a Fuji or Braeburn, two of the most flavorful apples currently produced in Washington orchards:
Bite into it. The first thing you get is the snap, the mouth feel. Then comes sweetness. Giving the flavor complexity is a varying amount of astringency or acidity. Then there's a salt taste. And finally--aroma.
Aroma is what makes an apple memorable. It actually composes much of what we call "taste." It adds depth to the eating experience. It gives the apple character.
So what happened to these beautiful Red Delicious (different strains of which make up 60 percent of the Washington apple crop)?
What gives apples their aroma is the release of volatile molecules, mostly esters, concentrated in the skin and outer flesh. Because most of the apple's color production also occurs in the skin, Fellman and his colleagues became interested in the biochemical relationship between color and aroma.
About 335 different compounds have been identified in the apple. Maybe 15 have a real impact on the apple's character, even at very low levels. The differences in taste among apples is mainly a result of varying mixtures of these compounds.
Early studies showed that paler color strains of Red Delicious had higher volatile ester content, the first clue to the color/flavor relationship. Fellman and his colleagues began to work on ways to manipulate color production. Other studies had shown that reduction in sunlight decreased "anthocyanin biosynthesis," or the production of pigment, so they used shading on the tree to control the amount of light and thus reduce color in the fruit.
The amount of light reaching the surface of the fruit had a marked effect. In general, less light resulted in less anthocyanin and more ester emission. Stronger sunlight resulted in more anthocyanin and less ester emission, reinforcing the conclusion that the trade-off for high color in these Red Delicious strains is lower flavor and aroma molecule concentrations.
So is this part of an anti-gustatory plot, a further attempt to elevate image over sensual pleasure?
Well, no, not on the part of the growers. They just try to deliver what the market wants. And studies have shown that consumers want their eating apples red--and the redder the better.
As a result, says Fellman, the practice has been to "select, select, select," for color. "All of a sudden," he says, "Red Delicious evolved into something nothing like the original. It's a beautiful apple, very sweet, good in storage--but the skin is kind of bitter, and the aromas just aren't there."
Now that Fellman knows that color and flavor are related, what next?
If he can determine exactly what controls that relationship, not only would it help in selecting for better strains of apple varieties, but it would help in manipulating storage conditions so the apples will taste better when they come out. Even under "controlled atmosphere" cold storage, apples continue to metabolize. Cell walls break down, esters dissipate.
But if Fellman can determine at what exact stage of maturation the apple should be picked and stored, then a "fresher" apple during the off-season will be the result.
Think about those apples you buy in early summer. Where do they come from? Well, either cold storage or the southern hemisphere. The primary challenge of controlled-atmosphere cold storage is maintaining the apple's flavor--so it can compete with the fresher imported apples.
Everything, some would argue, is a tradeoff. You can't have your color and flavor, too. But Fellman is trying to avert that tradeoff, figure out some way to breed for the color that consumers appear to like and still give the more demanding ones flavor along with it.
A key to determining how to store apples better might be the enzyme that directs formation of the esters, alcohol acetyl transferase or AAT. As the apple grows, aldehydes and alcohols occupy the green fruit, producing "green" aromas. The aldehydes reduce to alcohols. Then AAT takes an acetate molecule from a different biochemical pathway and hooks it to the alcohol to form the combination of volatile esters that give the fruit its ripe aroma.
"What we're thinking," says Fellman, "is ripening is a very complex coordinated set of biochemical events signaled by the presence of a hormone called ethylene." Once ethylene shows up, a lot of the AAT shows up, too. The metabolic activity of apples is very high right up until the onset of ripening, when it slacks off a little, then goes through another burst of activity. Being able to accurately detect the presence of AAT would give a more accurate indicator of the best time to pick for storage--which is when the apple is mature, but not completely ripe. Fellman has been working with the ATT enzyme for several years and just about has it pure, which is necessary to develop antibodies as indicators of its presence.
Most storage problems--not only loss of aroma, but also rot and other problems--stem from picking the fruit either too early or too late. Pinning down the metabolic processes of ripening will give growers great advantage in the ongoing globalization of agriculture.
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