Can dynamical mechanical measurements predict brittle fracture behaviour?

International audienceThe uptake of water by low moisture cereal products can have detrimental effects on their texture, and cause loss of quality. Following the interest in developing techniques suitable for determining texture properties, there has also been a move towards identifying the origins of the observed changes. Although the origins of the hydration effects are not fully understood, dynamic rheology is believed to be a suitable technique for characterising mechanical properties, and for identifying the origins of the features observed after moisture pick-up. In a previous paper, the sensory crispness of white bread and of extruded flat bread were correlated with tanδ, through the increase in tanδ resulting from the increased hydration associated with loss of crispness. The present work shows that such a correlation does not exist with extruded starch-sugar samples. This means that tanδ data cannot be used to predict fracture properties like those “covered” by crispness. The information revealed by the results did, however, address various questions about the significance of tanδ. Indeed, the increase in tanδ with increasing hydration was shown to be particularly acute when the starch was mixed with sugar (sucrose or fructose). In order to interpret these results several hypotheses have been suggested, including increased heterogeneity of the systems, and sensitivity of tanδ to solute mobility or to localised motions of the matrix