Physical, chemical, and sensory characteristics of dehydrated shiitake mushrooms

Shiitake mushrooms grown in Claiborne County, Tennessee were cryogenically frozen, held at -31°C until processing and then dehydrated in a Armfield forced-air, tray drier. The mushrooms were initially dried at 50°C for 3 hr and then finished at 40, 50, or 60°C for 6, 5 or 4 hr, respectively.

The shiitake mushrooms were then evaluated for free glutamate (MSG), water soluble carbohydrates (WSC) and ninhydrin reactive materials (NRM), proximate composition, color, and flavor strength. The flavor strength was evaluated by a sensory panel of 8 members from Asian countries selected on the basis of their familiarity with shiitake flavor and sensory methodology.

MSG and NRM were not significantly affected by dehydration conditions but increased under lower temperatures and longer times for dehydration and decreased slightly at higher temperatures and shorter times of dehydration. MSG increased from 3.11 mg/g in partially dehydrated shiitake to 3.12 mg/g in shiitake dried at 40°C for 6 hr, and decreased to 2.40 mg/g in the shiitake dried at 60°C for 4 hr. NRM increased from 29.2 mg/g to 32.8 mg/g and decreased to 25.1 mg/g under the same conditions. WSC was significantly affected by dehydration conditions. The WSC decreased from 3.63 mg/g in the partially dried shiitake to 2.47 mg/g in the shiitake dried at 60°C. The mushrooms dried at 50 and 40°C were significantly lower than the other treatments at 1.56 mg/g and 1.11 mg/g, respectively.

The shiitake mushrooms are mostly water, 88.2%, and the solid content is 76% carbohydrates of which 9% is dietary fiber. The dehydration temperature and time did not affect the proximate composition of the mushroom caps and stems. However, the mushroom caps contained more moisture, protein and ash while the stems contained more dietary fiber. The mushrooms decreased in lightness from a Hunter L value of 66.2 in the partially dehydrated caps to 42.4-43.7 in the completely dried caps.

Mushrooms that had second phase drying temperatures of 40 and 50°C had significantly stronger flavor than either freeze-dried mushrooms or mushrooms with a second phase drying temperature of 60°C. Mushrooms finished at 40 and 50°C were equal in flavor strength to two commercial shiitake samples and had a significantly stronger flavor than one commercial sample. Dehydrated stems were found to be similar in flavor to the dried caps.