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.

Abstract

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. 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-1 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. 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.