Optimization of the Technology of Hot Steam Blanching Coupled with Hot Air-microwave Combined Drying Process of Shiitakes

The influence of different heat steam treatment time (0, 60, 120, 180, 240 s) on the drying characteristics and color of shiitakes were explored in this study. The single factor test was carried out to determine a better pretreatment time. Drying experiments were performed in order to investigate the effect of hot air-intermittent microwave combined drying on the characteristics, energy consumption and quality (color, shrinkage mode, lentinan) at different pulse ratios (2, 3, 4, 5, 6). The optimal drying process was achieved. Results showed that hot steam blanching resulted in decreasing the drying time by 0%~30%, and the best quality was obtained at the blanching time of 180 s. In addition, by increasing the pulse ratio from 2 to 6, samples drying time and energy consumption decreased. The content of lentinan decreased initially, and then increased with the increment of the pulse ratio. The thickness ratio was related to the humidity ratio as a quadratic function during the drying process. The fitting coefficient was 0.83~0.97 when the pulse ratio was between 2 to 6, and the quadratic function fitted well. In fact, less color change, better maintenance of lentinan and less the energy consumption was achieved with the microwave intermittent ratio was 2 (1 min:1 min, t_on:t_off). Overall, 180 s hot steam blanching coupled with hot air-microwave combined drying achieved rapid drying and optimized the quality of dried shiitakes when the pulse ratio was 2.