Comparison of dynamic water distribution and microstructure formation of shiitake mushrooms during hot air and far infrared radiation drying by low-field nuclear magnetic resonance and scanning electron microscopy.

Background: An abundance of shiitake mushrooms is consumed in dried form around the world. In the present study, changes in water state, water distribution and microstructure of shiitake mushrooms during hot-air drying (HAD) and far-infrared radiation drying (FIRD) processes were investigated using low-field nuclear magnetic resonance and scanning electron microscopy. Quality attributes of the dried products were compared in terms of drying property, appearance, rehydration behavior, texture and storage stability.

Results: Compared with HAD, the rate of water diffusion and evaporation of the shiitake mushrooms dried by FIRD was higher, thus resulting in a shorter drying time (630 min), a lower water content (0.07 g g wet basis) and a higher glass transition temperature (7.88 °C) for dried products. Moreover, a homogenous and porous microstructure with less shrinkage and case hardening was demonstrated by the FIRD samples, indicating a superior texture, including a larger pileus diameter (3.4 cm), a higher rehydration ratio (7.31), a lower hardness (37.93 N) and a higher crispness (1.41 mm) for FIRD shiitake mushrooms.

Conclusion: High-quality shiitake mushrooms with a desirable texture could be produced by FIRD by enhancing the diffusion of internal water and alleviating the case hardening during a relatively short drying process. © 2018 Society of Chemical Industry.