ATLANTA -- Why do some foods, such as eggs, explode in a microwave oven?Why do microwave-heated TV dinners emerge with dried-out peas but frozenmashed potatoes? Why do microwaved French fries always come out soggy?For the first time, a Cornell University professor has explained thefundamentals of these processes, and his calculations, he says, could turnmicrowaving into a predictable science, resulting in more appetizing andnutritious foods in the future.
Ashim Datta, associate professor of agricultural and biologicalengineering, has developed mathematical and computer models to explain howdifferent kinds of food, and properties such as such as shape and size, areaffected by oven power and food placement during microwave heating.
"We believe that our models provide a quantum leap in understanding,simultaneously, how microwaves behave and their change in behavior asheating occurs," Datta says.
Datta and his co-researcher, Cornell graduate student Hua Zhang, willexplain their findings on heating patterns in microwave ovens to foodscientists at the Institute of Food Technologists (IFT) annual meeting hereJune 22 and 23. They believe their models will enable manufacturers toformulate foods according to the most successful size and shape formicrowaving and to issue far more accurate and precise microwavinginstructions. They also believe their findings will for the first timemake microwave sterilization, to increase length of food storage,commercially possible.
About 95 percent of American homes own a microwave oven, and food productsfor the ovens generate sales of more than a $4 billion a year.
"Many products have failed in the past because foods tend to get heatedunevenly and unpredictably," Datta says. About 90 percent of newmicrowaveable food products fail every year, he says. "Our comprehensiveknowledge base should permanently help improve the U.S. food industry'sability to deliver safer, more wholesome and higher quality conveniencefoods that are demanded by today's busy consumer," he says.
The two researchers' models provide a comprehensive description of whatgoes on in a microwave oven by linking the electromagnetics, heat transferand the biochemical changes in heated foods inside the oven. Theircalculations also indicate what produces non-uniform heating patternsduring microwaving.
For example, a frozen block of food does not absorb microwaves very well,but as it is heated and parts of the surface thaw, the thawed regions startabsorbing more and more energy. "As a result, as the outer layer thaws andstarts absorbing more and more energy, it serves as a sort of shield,preventing microwaves from getting to the inside of the food," says Datta."We can now quantitatively predict why parts of the food may boil whileother parts remain frozen."
In the case of an egg and other round foods, Datta explains that theirshape and size may result in the center getting heated first; if the foodis dense, the pressure from the developing steam near the center may not beable to escape fast enough and could cause the food to explode. "However,you would think a larger ball would merely take longer to heat, but that'snot true," Datta points out. "A small and large ball get heated incompletely different ways, and our models quantify these phenomena."
Datta believes the findings are likely to make large improvements in themicrowave sterilization of foods, by making foods more nutritious andtastier. To date, he notes, microwaving has not been used on a commercialscale because heating patterns have been too unpredictable.
Two years ago Datta reported on how moisture, heating rate and a food'sporosity interact during microwave cooking to produce sogginess orexplosions. The updated models also take into account how the behavior ofthe microwaves and properties of the food constantly change during theprocess. Within a few months Datta expects to have final calculationscomputed that relate the properties and size of a food item and itsplacement in the oven with what to expect in terms of heating and how toensure that heating is more uniform.
Zhang will present his paper on microwave sterilization at the IFT meetingJune 22. That paper won the competition for the best graduate studentresearch paper in the food engineering division of IFT. The paper onmicrowave heating of foods will be presented June 23.
The project on microwave heating patterns is funded by the U.S. Departmentof Agriculture, and the microwave sterilization project is funded by theU.S. Army.
Materials provided by Cornell University. Note: Content may be edited for style and length.
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