Researchers tantalize animal taste buds

A sweet burst of flavor – chocolate, perhaps, or butter pecan, or vanilla – tantalizes your tongue when you lick an ice cream cone. Though distinctive, how would you describe these tastes if you couldn’t talk? And what if someone invented ice cream cones that were the best nutrition possible to maintain your health, but the taste was no longer appealing?

Vicktoria Danilova of the School of Veterinary Medicine peers into a microscope to check the sensors on a probe attached to an animal’s taste bud nerves. The research may help develop more palatable feeds for farm and zoo animals. Photo: Tania Banak/Courtesy School of Veterinary Medicine

That’s the dilemma faced by researchers who are studying perception of taste among animals, which can’t provide feedback. True, scientists can arrange feed-preference tests, where an animal chooses one type of feed above another. But those tests can be drawn-out and cumbersome if one doesn’t even know where to begin formulating the feeds.

To address this issue, Göran Hellekant and his fellow researchers at the School of Veterinary Medicine have perfected a machine, the Taste-o-matic, that allows them to determine what an animal tastes based on a given oral stimulus – any of 32 different taste solutions that can tickle an animal’s tongue via a plastic tube.

It turns out that different species perceive tastes differently. Just because humans find something sweet doesn’t mean cows (or any other animal) will taste the substance in the same way. Cats do not perceive sweet tastes at all. Pigs are partial to bitter flavors. One specie’s ice cream may be another specie’s rice cake – or distasteful medicine pill.

Hellekant’s research in the Department of Animal Health and Biomedical Sciences ranges from tests to improve cow milk replacement formulas to making zoo animal diets more palatable.

One recent breakthrough was the discovery of brazzein, a rare sweet protein that is 2,000 times sweeter than sugar. Industry is now working with this protein to enhance taste in fruits and vegetables, and possibly develop a new tabletop sweetener from corn.

Hellekant’s associate, Tom Roberts, provides a tour of their laboratory. The maze of tubes, monitors and electronic equipment emits a quiet whirring punctuated by beeps as new readings occur. Another associate, Vicktoria Danilova, peers into a microscope to confirm that the sensors on her probe are attached to the appropriate taste bud nerves, then starts a solution flowing through the Taste-o-matic.

The researchers access the nerves through an incision behind the jaw, a technique developed by Hellekant to prevent damage. “Our patients are eating the day after surgery,” Roberts notes.

As solutions flow onto the animal’s tongue, a computer records readings from the nerves leading to the taste buds. Afterwards, Danilova will analyze the data to determine what response occurred, if any. The equipment is so sophisticated that electrical impulses can pinpoint the response of individual taste buds. This enables researchers to find and test the most active taste buds within a taste category (e.g. “sweet”) and see if a product initiates a quick response, or if it lingers, leaving an “aftertaste.”

Once researchers determine an initial level of taste response, the animal progresses to behavioral tests, where it chooses between foods. But the foods will have the specific taste built in to see whether the animal’s real-life preference mirrors the results of the taste test machine.

Taste is a complex issue. Taste tends to be shaped by evolution. Animals tend to prefer tastes of foods that grow readily in their environment.

“Some of the research we’re doing may save animals from extinction,” Roberts says. “For example, how can we make diets more palatable to zoo animals?”

Hellekant’s laboratory performs taste tests on many different animals, ranging from mice one week to calves or even monkeys the next.

Roberts says taste is the slowest sense to study because the taste buds can only be stimulated once per minute. “You have to develop a taste for taste research,” he quips.