February 20, 2013
Give a baby her first spoonful of mashed spinach or blended brussell sprouts and you can likely watch her face pucker up in shocked torment. Veggies tend to be a dreaded childhood bane for many youngsters, yet there are exceptions to the vegetable hate rule. Sweet potatoes and carrots, for example, tend to score highly. But why is that? As a general rule, much of our likes and dislikes spawn from sweetness – or at least our perception of it.
Evolutionarily, we’re programmed to like sweetness, since it’s indicative of calorie-rich sugar. Millennia ago, when we were just beginning our evolutionary journey as Homo sapiens, those individuals who preferred and thus consumed sugar had an edge. Sugar imparts a quick energy boost, so desiring, locating and consuming sugar-rich food could mean the difference between out-maneuvering a predator, keeping warm during a cold night or bearing healthy children. Our closest relatives, such as chimpanzees, also share this propensity towards the sweet. Chimps regularly concoct creative ways to brave beehives to reach the sweet honey inside.
In today’s world of car commutes, office jobs and sugary snacks, however, our attraction to sugar turns against us, helping to fuel an epidemic of obesity. The processed food industry realized this a long time ago when it dawned on them that cranking up the sugar content of even the most cardboard-like snack automatically makes it delicious to our primitive food brains.
But sugar, it turns out, is not the only sweetness driver. The sweetness of a farmer’s market strawberry or a hand-picked blueberry comes largely from volatiles, or chemical compounds in food that readily become fumes. Our nose picks up on and interacts with dozens of these flavorful fumes in any given food, perfuming each bite with a specific flavor profile. The sensations received by smell and taste receptors interact in the same area of the brain, the thalamus, where our brain processes them to project flavors such as sweetness. ”The perception of sweetness in our brains is the sum of the inputs from sugars plus certain volatile chemicals,” said Harry Klee, a researcher with the university’s Horticulture Sciences Department and Plant Molecular and Cellular Biology Program, said at the American Association of the Advancement of Science conference, held last week in Boston. “The volatiles act to amplify the sugar signal so that we actually think there’s more sugar in the food than is actually present.”
A dozen or more volatiles can occupy a single food. Some trigger the sensation of sweetness, others of bitterness or sourness. If we could better understand just how these chemicals interact in foods and in our brains, we could genetically tweak foods to be more to our liking.
Scientists from the University of Florida think that “fixing the flavor” of foods such as tomatoes would make them more appealing to shoppers, which on the long run may facilitate a healthier society. “If we make healthy things taste better, we really believe that people will buy them more, eat them more and have a healthier diet,” Klee said. “Flavor is just a symptom of a larger problem,” he continued. “We have bred crops for a higher yield, while quality and nutritional value have dropped.”
What we think of as flavor actually has a great deal to do with the subtle smells of volatiles. Not convinced? The researchers predicted as much. In Boston, they whipped out samples of gummy bear-like candy (raspberry and blueberry Sunkist fruit gems to be specific) to prove the power of volatiles to the audience. As instructed by the Klee and his colleagues, I pinched my nose shut tight, then popped the candy into my mouth, chewed and swallowed half of it. As if I had a seriously stuffed up nose from a bad case of the flu, the candy felt squishy and lackluster on my tongue. This bland sensation, the researchers explained, is taste. Now, they instructed unplug your nose, and swallow the rest of the gummy candy. A wave of intense sweetness hit me like a sugary rainbow of fruity flavor. This is olfaction at work, explained Linda Bartoshuk, one of Klee’s colleagues at the university’s Center for Smell and Taste. “Who experienced a rush of flavor and sweetness that seemed about twice as powerful as before?” she asked. In a room of around 100 people, about half the hands shot up.
Several years ago, Klee made a mission of saving the modern tomato’s flavor in the hopes of ultimately improving consumer health. Those efforts have led him down a winding vine of chemistry, genetics and food science.
Rather than starting his investigation with tomato growers–who are paid to churn out attractive tomatoes, not make a flavorful food–Klee began with consumers, or the people who buy and eat tomatoes. He wanted to understand what makes good and bad flavor on a molecular level. Figuring out the formula for creating a delicious tomato that still maintains the high yields and disease resilience of the watery, bland supermarket offerings could give growers an easy-to-implement toolkit for improving their offerings.
Klee and his colleagues ground up dozens of tomato variety, then asked 100 different people to sample the fruits of the researchers’ labor and report back on their favorites and least favorites. Using that feedback, the researchers could identify which of the tomatoes’ more than 400 volatiles actually drove flavor. What they found indicated that consumers prefer tomatoes with a perceived sweetness – emphasis on “perceived.”
For example, yellow jelly beans, a breed of tomato, contain around 4,500 milligrams of sugar per 100 milliliters. A matina tomato, on the other hand, contains around 4,000 mg per 100 ml. Yet people perceive matinas as being about twice as sweet as yellow jelly beans. Volatiles drive the perception of what we think is sweetness in these two tomatoes.
Typically supermarket variety tomatoes vary in their sugar content, but they usually range from around 2,000 to 2,500 mg per 100 ml. The cherry tomato varieties typically sit in the 3,000 to 3,500 mg per ml range.
Just 15 to 20 volatiles control the majority of a tomato’s flavor, the researchers found. ”Some of the most abundant chemicals in a tomato have absolutely no influence on whether people like it or not,” Klee said.
This knowledge in hand, they went about creating a recipe for the perfect tomato, which resembles an heirloom. Their ideal fruit represents the average of what the research participants ranked as their preferred tomato. While absolute individual preferences may vary by demographics, cultures and whether or not someone is a supertaster, Klee believes that nearly everyone would agree that “this is a really good tomato.”
The next step, Klee says, is to move those desirable traits into the high yielding varieties of tomatoes. In the lab, he and his team successfully crossed modern tomatoes with their perfected heirloom, creating a hybrid. The new tomato maintains the deliciousness of the volatile-laden heirloom but produces twice as much fruit and keeps the modern strain’s resistance to disease. So far, yields aren’t quite at the level to convince commercial growers to change their ways, but Klee believes production improvements will get his tomato to the marketplace eventually.
“Can volatiles enhance sweetness while reducing our use of sugars and artificial sweeteners?” Bartoshuk posed. “We think: yes.”
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