Scientists find ways to reduce oil intake in deep fried foods

Fried foods are staple especially in Western diets due to their distinct flavour and sensory characteristics. The frying process causes foods to develop unique textures related to their crispy outside and soft inside.

“People like fried products because of the texture and the taste, but they have been claimed to be an ultra-processed food that we should try to minimise in our diet”, explains Pieter Verboven of KU Leuven in Belgium, corresponding author of the publication. “Still, the final composition is more of a concern than the process itself”, he adds. Therefore, the KU Leuven research team are investigating ways to reduce oil content but preserve texture and taste.

When we fry food, we submerge it into hot oil that is more than 160 °C. This leads to very fast evaporation of water and creates internal pressure in the form of steam, which results in an expanding porous structure. “This process is extremely fast, in the order of seconds, and we don’t have the tools to see what happens in real-time, so we need to come to the ESRF to be able to track the process”, says Verboven.

A fryer on the beamline

The team came to ID19 to carry out high-speed 4D computed tomography on wheat flour dough, a common food material subjected to deep-frying. The experiments took place as the dough was frying in a custom oil fryer and afterwards, during the post-frying cooling, with the aim of investigating the structural deformation and pore formation, as well as oil uptake. “The experiment was extremely complex, as we needed to scan the sample submerged in oil very fast to track all the changes at the microstructural level”, explains Bratislav Lukic, researcher at the ESRF and co-author of the publication, “The fryer was also equipped with sensors and actuators to precisely control the process remotely. Thanks to high flux at high energy of the Extremely Brilliant Source, we were able to reach sub-second scanning times while maintaining microscopic spatial resolution, all that in a very large fryer, which is representative of the process.”

The oil fryer set-up on the beamline.

They visualised how the product expands due to steam during the frying process, which hinders the oil from getting inside. At the same time, the physico-chemical changes in starch and gluten structure determine the pore structure. The trick is to control this process well to create the desired texture with a crispy crust and fluffy interior. The team found that oil is absorbed mostly during the cooling of the fried dough and, in smaller percentage, during the frying process itself.

A question of temperature

The results show that higher temperatures lead to the formation of a distinguished crust with surface openings, facilitating greater oil absorption in small crust pores through capillary action. By heating the oil up to specific high temperatures, the scientists found that oil content of the final product varied from 14.4 % at 180 °C, 12.2 % at 150 °C, to 1.3 % at 120 °C. This indicates that temperature is a key factor that dictates the rate of oil uptake and its distribution. Still, frying is a delicate process that is food-specific, which leaves much room for perspectives.

“This study will help us formulate manufacturing protocols for deep-fried food that are healthier, without denying the consumer the sensory expectations from a fried product”, concludes Verboven. The upcoming steps in this project are to develop mathematical models using computational tools to optimise the process.

Bratislav Lukic, ESRF scientist and part of the team, on the beamline. Credits: S. Candé.

Reference:

Nature Communications, March 2025. DOI : 10.1038/s41467-025-57934-z.

Text by Montserrat Capellas Espuny