Changes in the morphometric, textural, and aromatic characteristics of shiitake mushrooms during combined humid-convective drying

Abstract

The effects of combined humid-convective drying (CHCD) on quality attributes of shiitake mushrooms regarding surface color, microstructure, texture, volatile compounds, and polysaccharides were investigated. Initially, mushrooms were subjected to various hot air drying (HAD) procedures, and the influential parameters (initial temperature, relative humidity [RH], and time) were optimized based on highest yield of polysaccharides. Among them, nonuniform drying was selected to design CHCD, with final parameters—initial temperature: 40 °C, maximum temperature: 60 °C, RH: 30%, and time: 28 h. CHCD produced shiitake mushrooms with less surface color changes (p < 0.05), softer texture, and less shrinkage (47.1 ± 1%) than conventional HAD. Scanning electron microscopy results showed a honeycomb-like pore-network in CHCD samples. The yield of polysaccharides, predominantly β-glucans as detected by MALDI-TOF and CP-MAS NMR, was 12.3 ± 0.5 g/100g in CHCD samples, significantly higher than conventional HAD (p < 0.05). A total of 51 significant volatile compounds were detected with higher concentration in CHCD compared with HAD samples using GC × GC-QTOF. Along with increasing shelf-life, CHCD process produces dry mushrooms with lower surface color changes, good preservation of internal structure, softer texture, lesser shrinkage, increased rehydration, increased content of polysaccharides, and volatile compounds compared with conventional HAD.