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Inside Iowa State, a newspaper for faculty and staff, is published by the Office of University Relations.

Aug. 10, 2006

Finding out what people like -- and why

by Teddi Barron

Just east of the library, across Morrill Road, there's an unusual laboratory where the finely calibrated instruments are people, the numbered specimens are food samples and the measurements are degrees of sweet, sour, juicy and tough.

Ken Prusa

Ken Prusa

You might know about this remarkable place -- if you're one of the hundred or so trained panelists called upon from time to time to evaluate a granola bar or a pork chop; or if you've ever volunteered to give a thumb's up (or down) to a new yogurt flavor or an organic chicken tender.

It's the Sensory Evaluation Unit, a research laboratory of the Center for Designing Foods to Improve Nutrition. And it's Ken Prusa's primary workplace. Prusa is a professor in food science and human nutrition and professor-in-charge.

Specialized facilities in the unit enable university and industry researchers to obtain sensory evaluations of food products and ingredients. Prusa and colleagues provide the know-how.

"If an animal health company develops a new feed additive for pigs, for example, they want to know if it has an impact on pork quality, so they come to us," Prusa said. "Companies like Tyson, Swift and Co., Elanco Animal Health and Niman Ranch don't have their own sensory units. We fill a void for third-party testing."

Red lights, small cubicles

The facility consists of an institutional-style kitchen; an evaluator training room with a large round table, chairs and a blackboard; and a series of cubicles for evaluators. Food samples are passed through 18-inch openings to evaluators who taste samples and respond to questions on a laptop. One of the most unusual features in the cubicles is the red lighting. It's used to mask the color of the food samples so panelists don't base their taste evaluations on anything visual.

Prusa and assistant scientist Chris Fedler conduct two types of sensory panels -- trained and consumer. In a trained panel, eight to 10 people are taught to rate a particular attribute, like tenderness or rancidity. In a consumer panel, 80 to 120 people (about 10 at a time) evaluate whether or not they like a food product.

Trained panelists are drawn from a pool of staff, faculty and students, and are trained for each particular product and research question -- for example, "Does does this feed ingredient effect the tenderness of this pork chop?"

"For training, we'll give them samples of pork that we know are extremely tough, extremely tender, extremely juicy, flavorful, not flavorful," Prusa said.

"Then we actually calibrate them on those extremes. It's just like calibrating any type of instrument. We define the high-end and low-end of the scale," he said.

When evaluating tenderness, for example, the researchers use a 150-point line scale with "not tender" on one end and "very tender" on the other. Panelists are trained through repetition to know exactly where a sample fits on the tenderness scale.

"It's amazing to me how good they can be. We use them as calibrated instruments."

Pork quality

Researchers tend to run trained panels first, then follow up with a consumer panel. The Sensory Evaluation Unit runs about two to three trained panels each week and five or six consumer panels each year. They've tested all kinds of things, such as the color of irradiated ground beef, the viscosity of an energy drink for the elderly and the flavor of flax oil-fed walleye.

Much of Prusa's own work, however, involves pork quality. He earned his doctorate from Kansas State University in food and nutrition with an emphasis in sensory evaluation.

"When I came to Iowa in 1985, it was obvious that if I was going to work with meats, pork would be a pretty good choice," he said.

At that time, the push was to make pork an extremely lean source of protein. In 1987, the pork industry launched its marketing campaign, "The Other White Meat," which was based on the public perception that chicken and turkey are more healthful than red meat, including pork.

Now, 20 years later, Prusa is part of a growing circle of scientists and leaders in the industry who think pork may be lean enough.

"So we're studying other attributes of the product to look for points of differentiation for value added," he said.

Buying based on pH levels

And he may have, more or less, stumbled onto a characteristic that could prove to be as significant to the industry as leanness.

"I was doing research in a meat packing plant and noticed that the Japanese export buyers always chose the darker pork," he said. "I wanted to find out why, so I evaluated some darker products."

Prusa's research showed the Japanese were selecting not by color, but by what color indicated: pH, a measure of acidity or alkalinity. Darker pork has a slightly higher pH than lighter pork. A higher pH means there's less acid -- acid that damages muscle proteins and causes meat to be pale and watery.

"Through sensory testing, we found pH to be a pretty strong driver of ultimate pork quality. Higher pH products are more tender, juicy and flavorful," he said. "It tuned us in to an opportunity to add value to pork products in the marketplace."

Producers and packers are learning that it's in their best interest to produce products with higher pH, he said. So how do they do that?

Genetics, processing and stress cause low pH.

"Chilling is a big factor in processing. It's critical to lower the temperature of the carcass fairly rapidly. Otherwise, the pH may drop too low before chilling can stabilize it."

There's also a growing emphasis on reducing the stress an animal experiences just before slaughter. Keeping animals as calm as possible is key.

"Stress causes a high metabolism rate, which creates a lot of adrenaline. When that happens right before slaughter, it causes a rapid pH decline. If there's a rapid pH decline in the hot carcass, it's even worse," he said.

Prusa is working with packers, processors and geneticists to take advantage of the pH factor.

"There's probably a premium market in the U.S. for higher pH pork. Some major retailers on the West and East Coasts are figuring out that the best pork is exported. We're looking at specific ways to provide them higher pH products," he said.

Some processors and packers are moving toward buying pigs on the basis of pH.

"We hope that through our work with packers and processors, we'll see higher pH products on the market soon. We're looking at ways of marketing products on the basis of the deeper, richer color and flavor. People can see the difference. Once they taste it, the better quality is obvious," Prusa said.

"If you tell the story correctly, back it up with scientific information and have a better product, consumers will buy it."


"If you tell the story correctly, back it up with scientific information and have a better product, consumers will buy it."

Ken Prusa, professor in charge of the Sensory Evaluation Unit