New microwave frying technique could make french fries much healthier

Researchers at the University of Illinois Urbana-Champaign are studying how microwave frying can improve the way French fries are made. Their findings suggest that combining traditional frying with microwave heating may reduce oil absorption while maintaining the crispy texture people expect. This approach could also shorten cooking times, making it appealing for large-scale food production.

"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 doctoral student Yash Shah outlined their findings in two recent studies focused on how microwave frying changes what happens inside French fries during cooking.

Inside the Frying Process

In one study, the team partnered with researchers at Washington State University to use a specially designed microwave fryer. This system operated at two frequencies, 2.45 gigahertz (similar to a regular microwave oven) and 5.8 gigahertz.

To prepare the samples, potatoes were rinsed, peeled, cut into strips, blanched, and salted. The strips were then fried in soybean oil heated to 180 degrees Celsius. During and after frying, the team measured temperature, pressure, volume, texture, moisture, and oil content.

A key challenge in frying is preventing oil from entering the food, Takhar explained. Early in the process, the potato's pores are filled with water, leaving no space for oil. As cooking continues, that water evaporates, creating empty spaces that allow oil to be drawn in through negative pressure.

"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.

How Microwaves Help Reduce Oil Absorption

Much of the frying process occurs under negative pressure, which increases the tendency for oil to be pulled into the food. The researchers aimed to extend the time under positive pressure and reduce the period when negative pressure dominates.

"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.

Because microwaves generate heat throughout the food, they promote vapor formation and help maintain internal pressure that keeps oil from being absorbed as easily.

Faster Cooking and Less Oil

Alongside the experimental work, the researchers developed mathematical models to better understand how different factors influence frying. This modeling allowed them to examine temperature, pressure, moisture, texture, volume, and oil content under different conditions, including 2.45 GHz, 5.8 GHz, and conventional frying.

The results showed that microwave frying led to quicker moisture loss, reduced cooking times, and lower oil uptake overall.

However, microwave frying alone does not produce the desired texture.

"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 Practical Solution for the Food Industry

The researchers suggest that existing industrial fryers could be upgraded with microwave generators, which are relatively low cost and widely available. This makes the combined method a practical option for large-scale food production.

The findings were published in two papers. The first, "The Effect of Conventional and Microwave Frying on the Quality Characteristics of French Fries," appeared in the Journal of Food Science and was authored by Yash Shah, Xu Zhou, Juming Tang, and Pawan Singh Takhar.

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).