A new study shows that by introducing microwave heating into the traditional frying process, it is expected to significantly reduce the amount of oil absorbed and shorten the cooking time of fried foods such as French fries without sacrificing the crispy taste. This work was completed by the food engineering team of the School of Agricultural, Consumer and Environmental Sciences at the University of Illinois at Urbana-Champaign, and the relevant results were recently published in a journal in the field of food science.
Fried foods are popular for their outstanding flavor, but high fat content is closely related to health risks such as obesity and high blood pressure. How to strike a balance between "delicious" and "healthier" has always been the focus of the food industry. Research leader and food engineering professor Pawan Singh Takhar pointed out that consumers say they want to be healthy, but when they actually buy, they are often impressed by the "aroma and taste". Although high oil content increases flavor, it also brings higher energy and calories. Therefore, the team's goal is to "reduce the oil content without significantly sacrificing taste and texture."
To this end, the research team focused on the so-called "microwave frying" technology and systematically analyzed its impact on the physical changes of French fries and other foods during the heating process. In the first experiment, the University of Illinois collaborated with Washington State University to develop a specialized microwave frying device that operates at dual frequencies of 2.45 GHz (close to the frequency of household microwave ovens) and 5.8 GHz. In the experiment, the potatoes were washed, peeled, cut into strips, blanched and pre-treated with salt, and then fried in soybean oil at 180 degrees Celsius. The researchers monitored the temperature, pressure, volume change, texture, moisture content and oil content of the French fries during and after the frying process.
Research points out that during the frying process, a large amount of fat enters the food, and the key link lies in the replacement mechanism of "water" and "oil" in the microporous structure of the food. At first, the micropores inside the potato are filled with water, leaving almost no space to accommodate the oil; as the heating proceeds, the water continues to evaporate, and the remaining gaps absorb the oil driven by "negative pressure." Takhar uses a "straw" as an analogy: blowing air into a straw is a positive pressure, which will "push" the liquid out; sucking with your mouth will create a negative pressure, and the liquid will be "sucked" up. The large number of tiny pores inside the potato are like "countless thin straws." When the internal pressure is negative, the oil will be continuously sucked in. It is estimated that about 90% of the time of the traditional frying process is in such a negative pressure state. Therefore, how to shorten the negative pressure stage and extend the positive pressure stage is the key to controlling the amount of oil absorption.
In contrast, microwave heating changes this pressure distribution process. Traditional ovens transfer heat from the outside to the inside, but microwaves can penetrate the material and start heating from the inside, stimulating the vibration of water molecules to generate more water vapor, thus pushing the overall internal pressure to the "positive pressure" side and inhibiting the penetration of grease into the pore structure. In the second study based on the numerical model, the team further characterized the migration behavior of heat, moisture and oil in French fries under different heating modes through mathematical simulation, and compared the trends of temperature, pressure, volume, texture, moisture content and oil content under 2.45 GHz, 5.8 GHz microwave conditions and traditional frying conditions. Results showed that microwave frying resulted in faster moisture loss, shorter cooking times, and lower oil absorption.
However, the study also found that if microwave frying is simply used, the finished product often has the problem of "soft texture and not crispy enough shell", making it difficult to meet consumers' expectations for classic French fries. Takhar pointed out that traditional heating methods are still needed to obtain the ideal crispy taste, so the most realistic route is to integrate the two methods into the same set of equipment: conventional frying is responsible for forming the ideal external crispy structure, and microwave heating is used to increase the internal pressure and reduce the entry of grease.
At the level of industrial application, the research team believes that large-scale continuous frying production lines are expected to be upgraded through external microwave generators. Since the microwave component itself is relatively cheap and quite popular, the introduction of the "microwave + conventional frying" combined process is technically feasible and is expected to be promoted in large-scale food manufacturing at a lower cost to produce low-fat French fries and other fried products that take into account both taste and health.