Insights into the texture of extruded cereals: Structure and acoustic properties

• Adding fibres strongly modifies hardness and acoustic emission of extruded cereals.
• The higher the aeration of the products, the lower the hardness and the higher the number of events.
• For a wide range of porosities, acoustic emission is strongly linked to the cellular structure.
• For similar porosities, acoustic properties are mainly explained by matrix properties.

Structure and texture of extruded cereals were investigated on products obtained from different flours (whole wheat flour and corn flour recipes) and for different fibre addition levels. Texture, i.e. mechanical properties, was assessed through a compression test and structure was analysed via microcomputed X-ray tomography and 3D image analysis. The addition of fibres at different levels in wheat and corn recipes strongly decreased porosity, thus leading to harder products. The acoustic properties, obtained from a contact method assumed to simulate biting and bone conduction of the sound, are also modified by the amount of added fibres. The acoustic properties can be related to product structure and mechanical properties.Industrial relevance
• This study was performed within the European InsideFood project and extruded cereals were produced in an industrial environment.
• The main objective was to find the drivers of texture changes in extruded cereals when fibres were added in the recipe.
• Texture measurements, i.e. mechanical properties of cereals assessed by compression tests are commonly used as physical measurements.
• Even though acoustic emission has largely been used before in previous studies, the method used here differs as it is a contact method.
• The uniqueness of this study was to combine structural information with physical results (hardness and acoustic emission), and to find out the main structure attributes that drive these physical attributes.
• Understanding the impact of structure on texture is key, since it helps in designing the right structure through the right processing conditions to target the desired texture properties.
• This study showed that cellular structure is key – however, another level that has also to be addressed is the wall structure – at the moment, we are still lacking convenient and quick methods to assess dispersion of protein, and fibres in the starch matrix (microscopy is time-consuming). It is known that it plays a role in the breaking behaviour of cereal products. We have seen here in our study that acoustic emission can be linked to the number of peak upon compression. This may reflect the structural organisation at the walls level.