Relative humidity control during shiitake mushroom (Lentinus edodes) hot air drying based on appearance quality

A relative humidity (RH) control method was proposed based on changes of shiitake mushroom ratio of wrinkled surface area (RWSA) obtained by computer vision technology (namely 30 %-RWSA) during which dehumidification fan was turned on with a sudden increase of RWSA. Three other RH control methods of continuous fanning, setting constant target RH (namely Whole process 30 %) and controlling RH based on RH change (namely 30 %-RH) were also carried out for comparison. Drying time of 30 %-RWSA group was significantly (p ≤ 0.05) shortened, while shrinkage, RWSA, rehydration ratio were insignificantly different from (p > 0.05) those of 30 %-RH group. The cell aspect ratio of continuous fanning group was the lowest. The results showed that the qualities of shiitake mushrooms could not be improved by shortening RH keeping time, shiitake mushroom should be dried in low RH environment. The Gaussian process regression (GPR) model was effective for on-line prediction of RWSA. •Longer humidity duration led to larger shiitake mushroom longitudinal deformation.•Rapid surface hardening maintained mushroom appearance quality and cell structure.•Higher rehydration ratio can be obtained by slow change of relative humidity.•Recurrent Gaussian process regression better predicted mushroom surface wrinkles.