The effect of the puncturing settings (crosshead speed and punch cross-section) on the crust mechanical parameters was investigated using breads with two different crust thickness. Results showed that, greater punch cross-section was associated to compression behavior, which reduced the sensibility to detect changes in the crust structure. Moreover, low crosshead speed (0.5 mm/s) puncture test provided information about the cellular structure of the crust. The relationship between the puncturing parameters and the water activity and moisture content together with the crust microstructure analysis revealed that for obtaining reliable information about the structural ruptures related to crispiness texture, it is necessary to use low crosshead speeds (0.5 mm/s) and low punch cross-section (3 mm2). Crust microstructure observations indicate that the crust layers and the size and shape of the air cells are responsible of the puncturing behavior.
Texture of the bread crust is an important parameter used to define the quality of crispy breads and their freshness. Consequently, the extension of crust crispiness is still a priority for the baking industry. Different methods have been proposed for assessing the mechanical properties of the bread crust, although punching is a common feature in all of them. However, there is no information about the incidence of punching settings on the bread crust mechanical parameters. Water activity and moisture content of the crust, besides scanning electron microscopy of the crust section, were used to confirm the reliability of the mechanical parameters. The study allows defining the best conditions to study the crust's mechanical properties providing information about the internal cell structure. Results could be very useful at research level and also for the baking industry when investigating crust freshness.