Rats and Machines Enlisted to Test Sweeteners

Rats and humans have more in common than you might think.

ByABC News
August 13, 2013, 6:25 PM

Aug. 14, 2013 — -- A cornucopia of artificial sweeteners is available in the grocery store: Equal, Nutrasweet, Sweet'N Low, Splenda and several others. To make it to the shelf, each had to go through a thorough research and development phase. Somewhere along the line, those companies enlisted people to taste each sweetener and see how it stacked up to regular sugar.

Opertech Bio, a startup in Philadelphia, says it can take humans out of the testing process and replace them with rats and machines. Kyle Palmer, the chief science officer of the company, says that the Microtiter Operant Gustometer, or MOG, could test hundreds to thousands of different flavor compounds quickly and easily. The design and results of the company's initial test runs are published in the journal PLoS One.

It may seem strange to use a rat to test for flavors that people might like, but the two palates have more in common than you might think. Alfredo Fontanini, a neuroscientist at Stony Brook University in New York, said that even if the foods that we eat are different from the garbage that rats feast on, there are still similarities. "As a rule of thumb, humans and rats dislike bitter, sour and very salty things," he told ABC News. "But we both like sweet and savory things too."

Palmer saw the machine as a middle ground between two different ways of taste testing. At one end are human taste tests in which people are given sample solutions to swish around in their mouths and judge how sweet, salty or sour something is. On the other end is a cellular biochemistry test in which taste receptor proteins are cloned, samples are piped in, and the research team observes whether a sample elicits a reaction from the receptor.

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"We saw that there was a real need for a real sensory test and not just a receptor activity test," said Palmer. In addition to producing quick taste tests, Palmer adds that the MOG can also run tests without wasting a lot of samples as it would compared with human taste panels. "It's like a transition from these cell tests to human tests."

The MOG measures two different aspects of taste, palatability and quality. The rat is presented with a sample to lick. If the rat licks the sample 10, 20 or even 30 times, then scientists infer that the sample has high palatability, that the rat enjoys the taste. A sweet sample will get up to 30 licks, while a bitter solution laced with quinine will only get two or three.

When the rat is done licking, it has been conditioned to press one of two levers, depending on how it perceived the taste, or the quality of the taste. Pressing the right lever says, "I am familiar with this taste," while pressing the left lever says, "This taste is foreign to me." If the rat was testing an artificial sweetener, it should press the right lever and identify the taste as similar to natural sugar.

"As a rule of thumb, humans and rats dislike bitter, sour, and very salty things."

Fontanini says that the logic and design behind the MOG is sound, but that there may be a more accurate way to measure whether a sample is palatable or not. It turns out that even rats make faces when they taste food. "When they taste something bitter, their mouth opens wide and the corners of the mouth go back," he said. "It's the yucky face, when you taste something and you go 'blech!'"

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