Drying behavior, color change and rehydration of lingzhi mushroom (Ganoderma lucidum) under convection-assisted microwave drying

Abstract

Lingzhi mushrooms (Ganoderma lucidum) are a highly valued agricultural product that is used for medicinal purposes due to its range of important nutrient contents. However, the mushroom is perishable, as it is sensitive to moisture. To increase its shelf life and maintain the quality, a hybrid drying technique of convection-assisted microwave drying was investigated in this study. In the experiment, 3-mm thick slices of lingzhi mushrooms were dried at a hot air velocity of 1 m/s, hot air temperatures (Tdry) of 50, 60, and 70 °C, and microwave powers (Mp) of 200, 400, and 600 W. The mass of lingzhi mushrooms was recorded every 5 min until there was no further change in mass. The experimental results presented drying behaviors in terms of dry basis moisture content (Mdb) and drying rate (DR). Additionally, the overall color differences (ΔE) and the percentage of rehydration (Rd) were assessed. The results demonstrated that the increase in Tdry and Mp resulted in the DR and ΔE increasing, while the drying time and Rd decreased. The highest DR of 8.6 gwater/min and the shortest drying time of 25 min were observed at a Tdry of 70 °C and Mp of 600 W. The L*, a*, and b* values of the dried lingzhi mushrooms showed significant statistical differences (p < 0.05) compared to the fresh samples. The ΔE was significantly affected by both Tdry and Mp, while the Rd was more influenced by Tdry than Mp, with a significance level of p < 0.05. The lowest ΔE and highest Rd values were achieved at Tdry = 50 °C and Mp = 200 W. Furthermore, the developed empirical model accurately predicted the moisture ratio (R2 > 0.9982 and RMSE < 0.0210).