Effect of high temperature hot-air blanching pretreatment on the quality of shiitake mushrooms under different hot-air drying modes

The low input and easily controlled hot-air drying (HAD) is the most widely used drying technology, while the quality of shiitake mushrooms varied with different drying temperature or pretreatment modes, driving exploration of environmentally friendly drying strategy that is conducive to product quality. The focus of this study is the effects of high temperature hot-air blanching pretreatment (100 °C, 10 min) combined with different HAD- modes (constant temperature at 35 and 65 °C, and temperature gradient at 35-65 °C) on quality of shiitake mushrooms. Overall, high temperature hot-air blanching induced darker color and severe shrinkage, caused higher extent of browning and cross-linking and aggregation of proteins, and reduced the chemical antioxidant capacities in mushrooms. For unblanched samples, compared to those dried at constant temperature of 35 and 65 °C, the sample under temperature gradient at 35-65 °C (G) showed lower browning degree based on color index and the absorbance at 420 nm, and a better appearance was also observed. The higher chemical antioxidant capacities were observed in G containing higher contents of free amino group and total phenols. The protein molecular weights of G were mainly ranged at 50-70 kDa, and proteins below 50 kDa were also widely distributed. In addition, the amino acid patterns suggested G had high-quality protein, which was rich in free amino acids with sweetness and umami. Thus, hot-air blanching may not contribute to the quality of dried shiitake mushrooms, and temperature gradient HAD without blanching could be a practical approach for drying of shiitake mushrooms. • Hot-air blanching prior to drying did not improve the quality of shiitake mushrooms. • Hot-air blanching induced higher extent of browning and cross-linking of proteins. • Temperature gradient hot-air drying achieved better quality of shiitake mushrooms.