Optimization of the drying process parameters for lentinus edodes in segment variable temperature infrared assisted spouted bed

Lentinus edodes are favored by consumers, due mainly to the antitumor, immunoregulation, anti-aging, antioxidation, and anti-radiation. However, the drying process can be used to extend the shelf life, because the fresh lentinus edodes are not easy to store. In this experiment, a new infrared-assisted spouted bed drying equipment was used to investigate the drying process of lentinus edodes under the segment variable temperature. An infrared-assisted spouted bed was utilized to improve the high energy consumption and heat loss of infrared drying with uniform distribution. A single factor Box-Behnken Design was used to optimize the response surface experiment. The parameters included the early wind temperature, water content at conversion point, and late wind temperature on specific power consumption, crude polysaccharide content, brightness value L* and shrinkage ratio. The polynomial regression was derived by a weighted comprehensive score to optimize the drying process parameters of an infrared-assisted spouted bed. The results showed that the crude polysaccharide content of lentinus edodes dried by infrared spouted assisted bed gradually increased, with the increase of early wind temperature (A), where the retention rate increased to a maximum of 9.33 mg/g at 60°C. The materials were also heated evenly during drying. The specific power consumption decreased to reach the minimum of 160.95 kJ/g, while the drying time was shortened, with the increase of temperature, when the early wind temperature was 60°C. Brightness value L* and shrinkage ratio showed a trend of first increased and then decreased, with the increase of early wind temperature at the maximum of 55°C. Appropriate early wind temperature could effectively reduce the specific power consumption, thereby maintaining high nutrients for better economic benefits. The content of crude polysaccharide increased significantly, where the maximum was 10.44 mg/g at 70°C, particularly when the late wind temperature (C) was 60°C-70°C. Furthermore, there was an obvious downward trend, when the temperature continued to rise. Excessive temperature could damage the retention of nutrients during drying, due mainly to polysaccharide degradation produced oligosaccharides and partial caramel. The drying rate accelerated, but the specific power consumption decreased, with the increase of temperature. In addition, there was the most obvious shrinkage ratio at 75°C, with the maximum yellow/blue value b* of 19.93, while the brightness value L* value continued to decrease, with the increase of late wind temperature. Correspondingly, there was a significant difference (P<0.05), particularly slightly browning, and yellow color of Lentinula edodes. The specific power consumption decreased gradually, with the increase of water content at conversion point (B). There was also a trend of first increasing and then decreasing in the crude polysaccharide content. The shrinkage ratio and brightness value L* increased first and then decreased, with the increase of water content at the conversion point. The single factor interaction was ranked in the order of AC>AB>BC. The optimal drying parameters were achieved using the response surface method, where the early wind temperature was 56.00°C, the water content at the conversion point was 53.00%, and the late wind temperature was 72.00°C. In this case, the specific power consumption was 143.52 kJ/g, the crude polysaccharide content was 9.98 mg/g, the brightness value L* value was 68.11, the shrinkage ratio was 83.15%, the comprehensive score value was 35.37, and the fitting degree with the predicted value was 99.27%. Consequently, the infrared-assisted spouted bed drying can widely be expected to fully meet the development trend and demand of lentinus edodes products. The finding can also provide a theoretical foundation for the production and processing of dried lentinus edodes products.