Research on Microwave Cooking Heats Up

Johnny Casanovas prepares to use a particle analyzer to observe how starch reacts when cooked in a microwave oven.

Heating a frozen entree in a microwave oven for five to seven minutes doesn't exactly take an advanced degree in physics. In fact, most homeowners have no idea how a microwave cooks food. They just set the timer and punch the "start" button. As it turns out, even food scientists don't entirely understand what is happening inside this ubiquitous appliance. They know how energy from electromagnetic waves cooks food, but they aren't sure how the individual food components react to microwave cooking. Food processors perfect cooking times for consumer products by long and costly trial-and-error experiments. Johnny Casasnovas, a doctoral candidate in food science, is looking to change all that–by cooking up a research model to help scientists predict how different food ingredients react to microwaves.

A native of the Dominican Republic, Casasnovas came to Penn State after earning a B.S. in chemical engineering at Pedro Henriquez Ure–a National University in Santo Domingo. He became interested in microwave research while working with food scientist Ramaswamy Anantheswaran. "My initial project was to find a way to sterilize food packaging materials using microwaves," Casasnovas explains. "Plastic waste is a big issue for the Navy and cruise ships because international law forbids ships to dump the waste into the ocean. As a result, plastic food packaging waste materials have to be stored on board until reaching port. The United States requires this incoming waste to be sterilized by heating to 212 degrees for 30 minutes before disposal."

Casasnovas' work on microwaving plastic waste sparked a deeper interest in predicting microwave heating during the cooking process. "People have been cooking with fire since prehistoric times, and we've used steam since the 1800s, so there is a vast pool of knowledge about how food behaves with these heating methods," Casasnovas says. "With microwaving, we assume that energy is coming in uniformly, that microwaves behave in a consistent manner, and that food components will react a certain way. But we don't have a complete understanding of how the food is cooking. In a microwave oven, part of the heating power is absorbed by the food material, which causes the temperature to vary during the cooking process. This means uneven and unpredictable cooking."

Casasnovas is trying to understand the dielectric properties of food components. These properties allow scientists to predict how microwaves behave as they are transmitted through a medium–be it air, water, concrete, or a chicken leg. For example, an electrical engineer analyzes the dielectric properties of concrete and steel to predict how radio signals will behave in a large city. It's slightly more complicated for food scientists. They must establish how these properties behave in every component of food before they can predict how food products will react during the micro-waving process. "Electrical engineers usually deal with a fairly uniform material," Casasnovas explains. "But food is a biological material, and its components are not uniformly distributed. A chicken leg is made of skin, fat, meat, and bone. It is an engineer's nightmare."

In addition, the dielectric properties of food components change as the temperature increases, making it even more difficult to predict how microwaves will behave. To understand how these properties change as food is cooked, Casasnovas is looking at starch, which he worked with on an earlier research project with Penn State food scientists Donald Thompson and Gregory Ziegler. Starch, along with fats and proteins, is one of the major components in all foods. "I'm trying to build a foundation of basic research to establish a model for other researchers," Casasnovas says. "Analyzing starch will establish benchmarks for understanding how micro- waves cook other food components."

Although many food scientists work in labs filled with test tubes and electronic equipment, Casasnovas is using customized household microwave ovens to heat starch particles. A system of plastic tubes stretches from the microwave oven to a nearby particle size analyzer. As Casasnovas heats the starch solution, laser light measures how much starch granules swell as the heating progresses. Previously, researchers measured heating by stopping the cooking process to take measurements. Casasnovas' design of a continuous monitoring system makes it possible to see immediately how particles of starch, a thickening component that swells when heated, are changed by heating. "Food scientists can use our method of continuous measurement to understand the behavior of carbohydrates, lipids, proteins, salt and other minerals, and moisture during microwave heating," Casasnovas says.

This research also can be applied to designing microwave heating systems for commercial food processors. In fact, predictions for how food components react to microwave heating would be even more accurate in an industrial application because the processors can precisely control the microwave power, the amount of food components, and the position of food during heating. At home, there are still variables such as power levels for various appliance brands and placement of food in the oven.

"If you can predict how a material acts under microwave heating, you can design better food products," Casasnovas says. "I'll know which sauce in a pasta dish will slow down the cooking process, or I can manipulate ingredients to make Salisbury steak cook faster. Once we know more about how microwaves interact with all food components, then we can build a computer model that can simulate the cooking process. Essentially we would construct a 'virtual microwave' that would eliminate the trial-and-error testing that food processors do now."

–John Wall