Infrared radiation cuts fat in gluten-free donuts: Study

Published in the Journal of Food Engineering​, the research found that using IR to finish off partially fried gluten-free donuts can significantly cut fat content while maintaining properties similar to that of a fully fried gluten-free donut.

However, when compared to IR-finished and fully fried wheat donuts, sensory analysis indicated a lower acceptance.

“The objective of this study was to determine the combination of par-frying and infrared parameters that produce the highest quality gluten-free donut, as determined by instrumental and sensorial analysis, in comparison to both fully-fried gluten-free donuts and fully-fried wheat donuts,”​ the researchers wrote.

Compared to the fully fried gluten-free counterparts, the IR-finished donuts fared well – being “instrumentally and sensorially similar”,​ they said.

However, they said that “no gluten-free donut was sensorially similar to the fully-fried wheat donuts”.​

“Developing gluten-free products with the same texture and taste as their wheat counterparts is an ongoing challenge in food science, and additional work should be performed to improve the gluten-free donut formulation to create a product more sensorially similar to wheat donuts,”​ they added.

Lower fat content​

Most of the gluten-free IR-finished donuts had a lower fat content than fully fried versions, with an average fat content of 23.7-28.2% compared to 27.2%.

When compared to the wheat control (fully-fried) donuts that had an average fat content of 33.7%, all had “significantly lower”​ fat levels.

This drop in fat content when compared to the wheat donuts is likely due to a shorter frying time, and therefore lower oil uptake, the researchers said, but also the rice flour, pregelatinized rice flour and methylcellulose coating used in the gluten-free donuts.

“The proteins in rice flour resist oil uptake during frying, resulting in a product with lower fat content as compared to fried products made with other types of flour,”​ they said.

They added that pregelatinized rice flour and methylcellulose coatings have also been shown to lower the fat content of fried foods and donuts.

When comparing the fat content of those donuts par-fried with an IR-finish, it is clear the IR also played a role in lowering the fat content, the researchers said.

Formulation and frying details​

The gluten-free donut formulation included rice flour, garbanzo bean flour, potato starch, tapioca flour, sorghum flour and fava flour, as well as pregelatinized rice flour for a thickener.

Fully fried gluten-free donuts were cooked in soybean oil for 130 seconds (65 seconds on each side) at a temperature of 182⁰C.

Fully fried wheat donuts were cooked for slightly longer - 140 seconds (70 seconds each side) – but at the same temperature.

Par-fried donuts were cooked for 32 seconds on each side and immediately transferred to a conveyor belt of an IR oven. Emitter heights and residence times were different for each trial.

Source: Journal of Food Engineering​​
August 2013, Volume 117, pages 399-407. Published online ahead of print, doi: 10.1016/j.jfoodeng.2013.03.012
“Effect of infrared finishing process parameters on physical, mechanical, and sensory properties of par-fried, infrared-finished gluten-free donuts”​
Authors: HS. Melito and BE. Farkas