Lang
Fried foods are hugely popular with consumers, but their high fat content can contribute to health problems such as obesity and high blood pressure. If the food industry could offer lower-fat options of comparable quality, people would find it easier to make health-conscious dietary choices.
Researchers at the University of Illinois Urbana-Champaign have explored microwave frying of french fries, producing insights that could help food manufacturers adjust their production methods. They propose combining conventional and microwave frying to deliver the required crunch and texture while reducing cooking time and oil uptake.
Lead researcher 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 the University of Illinois, said: "Consumers want healthy foods, but at the point of purchase their cravings often win out. High oil content adds flavour, but it also carries a lot of energy and calories. My research team is studying the frying process with the aim of achieving lower fat content without significant differences in taste and texture."
In two new publications, Takhar and Yash Shah, a doctoral student in the department, discussed the findings of their studies exploring what happens during microwave frying of french fries.
In the first study, the researchers collaborated with colleagues at Washington State University, who developed a special microwave fryer capable of operating at 2.45 GHz, similar to a standard microwave oven, and 5.8 GHz.
Potato samples were washed and peeled, then cut into strips, blanched and salted. Batches of the potato strips were then fried in soybean oil preheated to 180°C.
The researchers measured temperature and pressure during and after frying, along with the volume, texture, moisture and oil content of the fried samples.
Takhar said the challenge lies in preventing oil from entering the food during and after cooking.
At the start of frying, the potato's pores are filled with water, so there is no space for oil to seep in. But as frying continues, the water begins to evaporate, opening up the pore spaces, and oil is drawn into the food by negative pressure.
Takhar explained: "Think of a straw in a drink. If you blow air into the straw, that creates positive pressure and any liquid will be pushed out. But if you suck on the straw, the liquid moves up. Now imagine that food materials contain many tiny straws. When there is positive pressure, the oil stays out. But if there is negative pressure, the oil starts moving in."
Up to 90% of the frying process occurs under negative pressure, so there is a continuous potential for oil to be drawn in. The goal is to maintain positive pressure for longer and shorten the period of negative pressure to keep oil out of the food.
Takhar added: "When we heat something in a conventional oven, heat travels from the outside in, but a microwave oven heats from the inside out, because microwaves penetrate the material everywhere. Microwaves cause water molecules to oscillate, generating more steam and therefore shifting the pressure path towards the positive side. High pressure in microwave systems helps reduce oil penetration."
Running alongside the laboratory experiments, the second paper complements the findings through mathematical modelling, allowing a more detailed exploration of a range of variables in the frying process.
The researchers examined the effects of temperature, pressure, volume, texture, moisture and oil at 2.45 GHz, at 5.8 GHz and in conventional frying. Overall, they found that microwave frying produced faster moisture loss, shorter cooking times and lower oil uptake.
Takhar explained: "However, if you use microwave frying alone, you get food that is moist and not crunchy. To achieve a crisp texture and taste, you need conventional heating. So we propose combining the two approaches in the same unit. Conventional heating preserves the crunch, while microwave heating reduces oil uptake."
The researchers ultimately conclude that the continuous fryers used to produce fried foods at industrial scale could be modified by integrating microwave generators, which are inexpensive and readily available. The approach is therefore likely to be economically viable for industrial use.
Source: University of Illinois