The researchers from Austria and Switzerland used electric shocks to heat the gluten free bread from the inside, saving considerable energy and time compared to conventional baking in applying heat from the outside.
Gluten free (GF) batters typically present several technological challenges that limit the bread’s performance during conventional baking. However, the 2019 study published in Food and Bioprocess Technology found OH produced a superior bread due to the volumetric heating principle and faster heating rates.
Effect on physical, nutritional properties of gluten free bread
The Ohmic bread was 10%-30% higher in volume compared to the control bread, had a crumb that was softer and more elastic, and pores that were smaller and more evenly distributed.
What is Ohmic heating?
The principle of OH – also known as joule heating – is well known from the light bulb: an electric current passes through a conductor and heats it up, resulting in a glow.
This is due to its electrical resistance and what’s known as Ohm’s Law – developed by German physicist George Ohm in 1827 – which leads to the dissipation of electrical energy into heat.
The resistance of bread dough results in the same effect, although it doesn’t glow, but heats up and bakes.
Tests performed by in-vitro methods also revealed OH did not impact the bread’s nutritional aspects. In fact, while starch digestibility was slightly reduced, this resulted in a bread with a higher resistant starch content, which is associated to several health benefits.
And perhaps best of all, the bread was made with less time and energy – a major advantage for the manufacturing industry.
Trials indicated savings of around two-thirds compared to the energy needed for conventional baking, while the dough was converted into a ready-to-eat bread in just a few minutes.
“In order to really benefit from these advantages and obtain best results, the optimal process and product characteristics had to be identified,” said Prof Henry Jäger of the Institute of Food Technology of the University of Natural Resources and Life Sciences (BOKU) in Vienna, Austria.
“Achieving such convincing results and improving the efficiency of the process at the same time was also surprising for us.”
The Ohmic bread was much lighter in colour than the control bread and the scientists concluded the Maillard reaction – and thus even possibly acrylamide – can be controlled or even minimised during OH.
A crust was not produced with OH, however, the researchers said this could be formed after ‘baking’ with infrared heating.
OH's advantage of instantaneous heat
The slow heating of conventional baking is a major limitation in manufacturing gluten free bread.
Wheat protein – or gluten, which is responsible for the dough structure and its expansion – is missing in gluten free products, so starch is typically substituted. Heat causes the starch to gelatinise, which contributes to the structure.
However, as gluten free bread formulations require a much larger portion of water, this results in a lower dough viscosity and makes it thinner and more liquid.
The scientists found gas retention was reinforced due to a better structure fixation at an early baking stage, resulting from the rapid and uniform heating of the whole dough mass during OH, particularly benefiting the production of gluten free bread.
“The heat is generated instantaneously within the complete dough. This is the main advantage of the Ohmic heating technology,” added Prof Jäger.
“Conventional baking in the oven requires more time, since the heat needs to penetrate from the outside toward the centre of the dough.”
Heating rate and holding time
The Ohmic heating of the breads was performed in a pilot scale OH unit from the German Institute of Food Technologies and was achieved by performing trials applying different combinations of electrical power input and duration of different baking steps.
“At the end, the subsequent application of three different process intensities with different holding times proved to be the most suitable option,” said Prof. Jäger.
“An initial baking step at two to six kiloWatts (kW) for 15 seconds followed by 1kW for 10 seconds and a final baking at 0.3kW for five minutes is the recipe for the successful production of gluten-free bread using Ohmic heating.”
Authors: Denisse Bender, Maximilian Gratz, Henry Jäger, et al.
Food and Bioprocess Technology, September 2019, Volume 12, Issue 9, pp 1603–1613
Authors: Diane F. Birt, Terri Boylston, Suzanne Hendrich, et al.
Advances in Nutrition, Volume 4, Issue 6, November 2013, Pages 587–601