French fries and other fried foods are popular largely because of their crisp texture and rich flavor. However, they can absorb large amounts of oil during cooking, increasing their fat and calorie content. Regularly consuming foods high in fat can contribute to health problems such as obesity and hypertension.
Researchers at the University of Illinois Urbana-Champaign are investigating whether microwave energy could help produce French fries that absorb less oil without losing the qualities consumers expect. Their findings suggest that combining microwave frying with conventional frying could shorten cooking time, limit oil uptake, and still create the crisp exterior and satisfying texture associated with traditional fries.
Creating Healthier Fries Without Sacrificing Flavor
“Consumers want healthy foods, but at the time of purchase, their cravings often take over. High oil content adds flavor, but it also contains a lot of energy and calories. My research team studies frying with the aim of obtaining lower fat content without significant differences in taste and texture,” said principal investigator Pawan Singh Takhar, professor of food engineering in the Department of Food Science and Human Nutrition, part of the College of Agricultural, Consumer and Environmental Sciences at U of I.
Takhar and Yash Shah, a doctoral student in FSHN, reported their results in two new publications examining the physical changes that occur when French fries are cooked with microwave energy.
For the first study, the Illinois researchers worked with scientists at Washington State University who had developed a specialized microwave fryer. The device could operate at both 2.45 gigahertz (similar to a regular microwave oven) and 5.8 gigahertz.
Gigahertz is a unit used to describe the frequency of electromagnetic waves. Different microwave frequencies can affect how energy moves through food and how quickly water molecules respond during cooking.
Tracking What Happens Inside a French Fry
The researchers rinsed and peeled potatoes before cutting them into strips. The strips were then blanched, salted, and fried in soybean oil that had been heated to 180 degrees Celsius.
Blanching briefly exposes food to hot water or steam. For potatoes, this step can begin softening the tissue and help prepare the surface for frying.
During and after cooking, the team measured temperature, internal pressure, volume, texture, moisture, and oil content. These measurements helped reveal how water escaped from the potatoes and how oil entered the spaces it left behind.
According to Takhar, one of the central challenges in frying is preventing oil from moving into food both during cooking and immediately afterward.
At the start of frying, the tiny pores inside a potato are still filled with water, leaving little room for oil. As the potato heats up, however, that water turns into vapor and escapes. Empty spaces begin to form, and negative pressure can pull oil into the potato.
“Think about a straw in a drink. If you push air into the straw, it creates positive pressure and any liquid will be pushed out. But if you suck on the straw, the liquid moves upward. Now imagine food materials have lots of tiny straws. When there is positive pressure, the oil stays out. But if there is negative pressure, the oil starts moving in,” Takhar explained.
Why Pressure Determines Oil Absorption
The researchers found that as much as 90% of frying occurs while the food is under negative pressure. That creates a prolonged suction effect, allowing oil to move into the newly opened pores.
A more effective frying process would keep pressure inside the potato positive for a longer period and reduce the amount of time spent under negative pressure. This could limit the amount of oil drawn into the food.
Microwave energy may help by heating water throughout the potato rather than relying only on heat moving inward from the surface. As water molecules absorb microwave energy, they move more rapidly and generate additional vapor. That vapor raises the pressure inside the food and makes it harder for oil to enter.
“When we heat something in a conventional oven, the heat moves from outside to inside, but a microwave oven heats from the inside out, because the microwaves penetrate everywhere in the material. The microwaves oscillate water molecules, causing more vapor formation and thus shifting the pressure profile towards the positive side. The higher pressure in microwaves helps reduce oil penetration,” Takhar said.
Microwave Frying Cuts Cooking Time and Oil Uptake
Alongside the laboratory tests, the researchers used mathematical modeling to examine the frying process in greater detail. Computer models allowed them to explore how different variables interacted and to predict changes that would be difficult to measure directly in every experiment.
The team compared temperature, pressure, volume, texture, moisture, and oil absorption during frying at 2.45 GHz, 5.8 GHz, and under conventional conditions.
Across the experiments and simulations, microwave frying caused moisture to leave the potatoes more quickly. It also reduced total cooking time and lowered the amount of oil absorbed by the fries.
Microwave frying by itself, however, did not produce the desired texture. Fries cooked only with microwave energy tended to remain soft rather than developing the crisp surface consumers expect.
“However, if you just use microwave frying, you get soggy food. To obtain a crispy texture and taste, you need conventional heating. Therefore, we propose combining the two approaches in the same unit. Conventional heating maintains the crispiness, while microwave heating lowers the oil intake,” Takhar said.
A Hybrid Fryer Could Offer the Best of Both Methods
The proposed system would use conventional frying to brown the surface and create crunch, while microwave energy would speed moisture removal and help prevent excess oil from entering the potato.
This combined approach could allow manufacturers to produce fries with less oil while preserving the flavor and texture that make fried foods appealing. Faster cooking could also improve production efficiency.
The researchers noted that continuous fryers used in large food processing facilities could be modified to include microwave generators. Because these components are widely available and relatively inexpensive, the system may be economically practical for commercial production.
The first paper, “The Effect of Conventional and Microwave Frying on the Quality Characteristics of French Fries,” is published in the Journal of Food Science.
The second paper “Predicting the quality changes during microwave frying of food biopolymers by solving the hybrid mixture theory-based unsaturated transport, and electromagnetics equations,” was published in Current Research in Food Science.
The research was funded by USDA National Institute of Food and Agriculture (Awards 2020-67017-31194, ILLU-698-308, and ILLU-698-926).