A penetration test was performed on the shiitake mushroom cap using a TA.XT2i texture analyzer (Stable Micro Systems, UK), using a 5 mm diameter cylindrical probe. Samples were penetrated 5 mm in depth. The speed of the probe was 2.0 mm s
during the pretest and penetration. Force and time data were recorded with Texture Expert (version 1.0) from Stable Micro Systems. From the force vs. time curves, firmness was defined as the maximum force.Measurements were performed in duplicate on three mushroom caps for each sample.