Product development of dried shiitake mushroom using belt-conveyor combined microwave-hot air drying

Abstract

Drying an agricultural product with hot air (HA) method causes a long drying time, and results in high specific drying energy consumption (SEC). The dried product has high shrinkage percentage and low rehydration. Therefore, this research aims to develop dried shiitake mushroom using belt-conveyor combined microwave-hot air drying method (MHB). The shiitake mushroom was dried by MHB at microwave power of 300 W, 400 W, 500 W and 600 W, and air temperature of 65 oC with air velocity of 0.3 m/s and recycled air of 80% and by the HA drying method at air temperature of 65 oC. The samples were dried until their final moisture content less than 11.1% dry basis. The drying kinetics, SEC of drying process and quality of dried shiitake mushroom were evaluated. The quality of dried product was considered in terms of color, shrinkage, rehydration, texture, water activity and microstructure. The results showed that the shiitake mushroom drying using MHB gave higher drying rate than that of HA drying method, leading to short drying time, and resulting in low SEC. The drying rate of un-blanched shiitake mushroom was higher than that of blanched shiitake mushroom. Dried shiitake mushroom from MHB drying gave lower values in shrinkage percentages and hardness, but higher rehydration and larger pore size than that dried by HA drying. However, the color values (L*, +a* and +b*) of dried shiitake mushroom in all cases were not significantly different. Meanwhile, dried shiitake mushroom from un-blanched case gave lower values in shrinkage percentage and hardness, but higher values in all colors and rehydration, and larger pore size than those of blanched case.