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It is hardly a scoop to say that bread, especially white bread, is one of these cereal products ranked as a high glycaemic food.  Formulation of bread with enhanced health benefits goes hand-in-hand with preserving its taste as much as possible. This can be done if its texture and oral behaviour are better understood.

Chewing bread is like putting a piece of an airy material between compression stages. During human mastication, muscular activity provides the necessary mechanical action to break down the food into pieces before swallowing. Most people do not even think about what the actual food undergoes during chewing, although it is determinant for the other steps of digestion. The sensory perception of bread chewing is unlike that of brittle cereal products, even if both share the same airiness.

In this study, we focus on the human mastication of bread in order to understand the complex physical phenomena behind its oral processing from the mechanical point of view. We capture the structural modifications that a piece of bread crumb undergoes during a compression test that mimics human mastication. This study is based on in situ 3D imaging conducted simultaneously with the mechanical action. The combination of both techniques reveals the internal modifications of the air cells composing the bread crumb structure at all stages up to product degradation. For the very first time, we provide a new mechanical interpretation of bread chewing based on the state of densification. Computerized tomography (CT) scans show that bread crumb loses up to 80% of its airiness, measured as a percentage of air in the crumb, before mechanical degradation begins. Airiness loss occurs while preserving the structural integrity of the bread crumb. Neither production of airy fragments nor loss of cell walls is observed before the onset of densification. This means that the preliminary step to food breakdown is the severe densification of bread crumb. This remarkable stability of the airy structure of bread is more obvious for hydrated bread. Densification can therefore be considered as a significant step in the oral processing of bread.

The formulation of healthy bread with a high nutritive value implies improved control of oral processing by considering densification as a texture criterion of product acceptance.

Publications

GUESSASMA, S. & NOURI, H. 2015. Compression behaviour of bread crumb up to densification investigated using X-ray tomography and finite element computation. Food Research International (2015), 72, 140-148. https://doi.org/10.1016/j.foodres.2015.03.038

GUESSASMA, S. & NOURI, H. 2016. Comprehensive study of biopolymer foam compression up to densification using X-ray micro-tomography and finite element computation. European Polymer Journal (2016), 84, 715-733. https://doi.org/10.1016/j.eurpolymj.2016.09.059