Comparison of Dynamic Water Distribution and Microstructure Formation of Shiitake Mushrooms during Hot Air and Far Infrared Radiation Drying by LF‐NMR and SEM

Abstract

BACKGROUND: A large number of shiitake mushrooms are consumed in dried form around the world. In this work, the 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 (LF-NMR) and scanning electron microscopy (SEM). Quality attributes of the dried products were compared in terms of drying property, appearance, rehydration behavior, texture and storage stability. RESULTS: As compared with HAD, the rate of water diffusion and evaporation of the shiitake mushrooms dried by FIRD was higher, thus resulting in shorter drying time (630 min), lower water content (0.07 g/g w.b.) and higher Tg (7.88°C) of dried products. Moreover, homogenous and porous microstructure with less shrinkage and case hardening was owned by the FIRD samples, indicating superior texture, for instance, larger pileus diameter (3.4 cm), higher rehydration ratio (7.31), lower hardness (37.93 N), and higher crispness (1.41 mm) of the FIRD shiitake mushrooms. CONCLUSION: High-quality shiitake mushrooms with desirable texture could be produced by FIRD through enhancing the diffusion of internal water and alleviating the case hardening during a relatively short drying process.