Optimization of shiitake mushroom vacuum tempering drying process based on imaginary calculation of its shrinking rate

Analyzing the area shrinking rate of shiitake mushroom before and after drying with digital image processing technology is an effective method to estimate the drying characteristics of shiitake mushroom. It is a valid measure to improve the drying quality of shiitake mushroom and save the energy by the vacuum tempering (discontinuous) drying. Based on the quadratic regression orthogonal experimental design with four factors and five levels, the effect of four factors, which including vacuum of the drying chamber, temperature of the heating plate, moisture content at the tempering moment and the tempering period, on the area shrinkage and the drying period during drying process was studied and the multiple regression mathematic model was established. The vacuum tempering drying process parameters of shiitake mushroom was optimized and verified with the multi-objective nonlinear optimization theory, and the optimal process parameters are as follows: the heating plate temperature is 70℃, the vacuum of the drying chamber is 0.09 MPa, the moisture content at the tempering moment is 70% and the tempering period is 11.3 min. These parameters can be a guidance for practical Shiitake drying.