Abstract
The histological structures of the parts of Shiitake mushrooms where we felt firmness by sensory evaluation were observed by a microscope in order to reveal the adequate position and direction of the sample for measurements of texture. From the microphotograph of frozen unfixed fresh Shiitake mushrooms stained with periodic acid Schiff, differences were found in the density of the hyphae. The hyphae showed a high density of 1-2 mm in width at the base of the gills in the pilleus, but in the interior of the pilleus, they showed a low density. This result showed that the central parts of the pilleus which were used in previously reported examples were not suitable for measuring the firmness of Shiitake mushrooms. Consequently, we must shape the Shiitake mushroom to include the base of gills in the pilleus, and the plunger must touch them in parallel with the stem.
Shiitake mushrooms were placed on a doughnut-type platform so as to meet these conditions, and the penetrating tests were carried out with a 1.5-mmφ cylindrical plunger. As a result, we could determine the rheological properties of Shiitake mushrooms and moreover, the parameters of the breaking properties, which represent the index of firmness, especially the breaking strain, were in good agreement with the firmness determined by sensory evaluation. This result shows that the position and direction of the Shiitake mushroom used in our experiments is appropriate.
