MECHANICAL-PROPERTIES OF THE MUSHROOM, AGARICUS-BISPORUS

Texture is an important factor contributing to mushroom quality. An improved technique to measure tissue compressive stiffness (ratio of stress-to-strain) by subjecting small specimens to a standard deformation has demonstrated that the stipe is strongly anisotropic, being ca 5 x stiffer longitudinally (i.e. parallel to hyphal orientation) than transversely. The pileus tends to be stiffer radially but is not consistently anisotropic. The upper and lower stipe are mechanically distinct, the former having a higher density and stiffness. In upper and lower stipe tissue, stiffness is proportional to density. After harvest both stipe and pileus tissues lose stiffness rapidly, the rate of loss being temperature-dependent. When mushrooms are allowed to develop before harvest (i.e. while still in contact with the mycelium), developmental stage has little effect on stipe stiffness whereas the pileus loses stiffness rapidly as the cap opens. During post-harvest storage at 18-degrees-C, pileus and stipe stiffness are negatively correlated, the relationship becoming more pronounced with increasing storage time.