Mechanical stress distributions in cross-sections of cucumber cultivars during the fracture process

The fracture process of six cucumber cultivars was examined to explore the mechanical properties that determine cultivar-specific crispy and crunchy textures. The postfailure portion of the load-strain curves was targeted in cucumber compression tests. The series of fractures after the initial fracture were examined at the tissue level by expressing the two-dimensional stress intensity as a map. The stress map for the difference between the fracture point and 0.01 s after the fracture point indicated that the stress distribution changed in a broad area for two cultivars (D and F), while it changed locally and in a small area for two other cultivars (A and E). Several load drops were observed on the load-strain curve for the cucumbers. The peak number between the fracture and the local minimal points was quite small for cultivars D and F, whereas it was substantial for cultivars A and E. A global fracture event occurred over the entire cross-sectional area at the initial fracture for cultivars D and F. The initial fracture occurred locally for cultivars A and E, and there were repeated sequential small local fractures as sample compression progressed. Two other cultivars (B and C), typical of those normally eaten raw, showed intermediate values for most parameters. This measurement provided the first demonstration of structural fracture during a series of load drops. How these postfailure properties will be associated with the texture characteristics of cucumber cultivars is discussed. (c) 2005 Society of Chemical Industry.