3D in situ analysis of the baking of gluten-free bread

Gluten-free breads often do not reach the same quality as their wheat-based counterparts. They often obtain less volume and age faster, which in turn can be improved by adding modified potato starches. For the understanding of how the properties of different types of starches affect the time-dependent bubble formation that increases the volume, it is important for the industry to be able to analyse different part of the baking process in real time.

Different types of starches

Lyckeby, Sveriges Stärkelse-producenter wanted to investigate how different types of starches affect the time-dependent bubble formation that increases the volume of gluten free bread. To carry out the experiment, they developed gluten-free doughs based on a benchmark recipe of Garbo Food, a speciality bakery specialising in gluten and dairy-free bakery products, with the addition of different potato starches (native or modified) which were produced and fermented at the TOMCAT beamline at the Swiss Light Source of Paul Scherrer Institute (PSI) in Switzerland. An Electrolux oven sample environment of RISE, allowing both convective and microwave baking, was used and samples were analysed during microwave-convective or convective baking. The retrogradation (ageing) of the finished baked bread was determined after storage by measuring the crystallinity of the nanostructure with laboratory SAXS-WAXS.

A slight collapse of the pores

With synchrotron data, pores and the bread material in the form of lamellae were visualized and distinguished very clearly, and the pore size, porosity (i.e. proportion of pores) and thickness of the lamellae were all quantified in 3D. A surprising structure development of the gluten-free bread was the stalled increase of porosity during convective baking followed by a decreased. The visualisation showed that this indicates a slight collapse of the pores, which may be due to the lack of gluten that can hold the pore structure together. Combination baking with microwaves, on the other hand, shows a continuous increase in porosity throughout the baking process. Gluten-free bread with modified starch addition showed a somewhat higher porosity and thinner lamellas compared to addition of native starch using combined baking. The retrogradation, measured as peak intensity ratio between B and V-type starch, showed that all gluten-free breads retrograded a lot after storage for three days in room temperature, especially bread containing non modified native starch and the bread baked using combination baking. After freeze storage there was low retrogradation found, except for the bread containing native starch that also retrograded in the freezer.

Facts/Analysis of gluten-free bread

1. Porosity and volume development:
   - Gluten-free bread tends to have a lower volume than bread baked with wheat flour, because it lacks gluten, which is important to hold the pore structure together.
   - In convection baking (regular oven baking), a surprising collapse of the pore structure was observed in the gluten-free bread, leading to a reduced porosity.
   - In combined baking with microwaves and convective heat, porosity increased steadily throughout the baking process, resulting in a high porosity of the final baked bread.
    
2. The effect of modified starch:
   - Gluten-free bread with added modified potato starch had higher porosity and thinner lamellae (the walls between the pores) than bread with natural starch, especially in combined baking.
   - Thus, modified starch improved the structure of the bread by increasing porosity, resulting in a more airy bread.
    
3. Retrogradation (ageing of the bread):
   - All gluten-free breads, regardless of the type of starch, showed high retrogradation, i.e. rapid aging, after three days of storage at room temperature. This means that the bread quickly becomes stale and loses its freshness.
   - Bread with natural starch aged faster than bread with modified starch.
   - After freezer storage, retrogradation was generally low, except for bread with natural starch, which also aged quickly in the freezer.
    
   Conclusion:
   Modified starch improves both the porosity and the texture of gluten-free bread, especially when baked with a combination of microwaves and convective heat (as in a “regular” oven). In addition, modified starch slows down the ageing of the bread compared to natural starch.