Effect of water activity on the mechanical properties of selected legumes and nuts
1997
Borges, A. | Peleg, M.
Two legumes (kidney beans and chickpeas) and two nut kernels (almonds and hazelnuts) were compressed intact with a Universal testing machine at various a(w) levels in the range of 0.11-0.85 at an ambient temperature of 22 degrees C. Mechanical characterisation of the four was done through four parameters; the slope of the initial part of force-displacement curve, considered a measure of stiffness, the failure force, considered a measure of strength, the deformation at failure, considered a measure of brittleness or deformability and the area under the force-displacement curve corresponding to 20% compression, considered a measure of toughness. Among these parameters only the latter could be determined and used effectively in all four seeds and along the whole water activity range. The jaggedness of the force-displacement curve was also determined in terms of its apparent fractal dimension calculated with two different algorithms for verification. There was a noticeable difference between the mechanical behaviour of the two groups. The nut kernels, apparently because of their high oil content, had a much smoother force-displacement curve, and the effect of absorbed moisture on their texture was generally more moderate than on that of the legumes. But in all the four types of seeds tested, each mechanical property had its own specific moisture dependency, an observation consistent with previous reports on cereal-based products.
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