Effects of different drying technologies on the drying characteristics and quality of Dictyophora rubrovolvata

Dictyophora rubrovolvata is one of the edible mushrooms in China. In this study, the drying quality of Dictyophora rubrovolvata was improved to obtain the optimal drying parameters. Different drying modes are included, such as vacuum infrared drying (VID), air impingement drying (AID) and moisture control drying (MCD). The hot air drying (HAD) was treated as the control group. A systematic investigation was made to reveal the effects of different modes and drying temperatures on the drying quality. The results showed that there was a significant effect of drying modes on the macroscopic quality (P<0.05). MCD was achieved in the smallest color difference (ΔE) and the lowest shrinkage rate, while AID was in a higher rehydration ratio. But the VID group was not conducive to the dehydration, due to the low ΔE value, the rehydration ratio, and shrinkage rate. The highest drying rate was observed in the MCD at the early stage, and then gradually slowed down at the later stage. While the AID obtained the shortest drying time and always maintained a relatively high drying rate during dryings. The drying time of the VID group at different temperatures from 60 to 45 °C was 600, 750, 900 and 1 440 min, respectively. Owing to the infrared emission mismatching the natural frequency, the overall drying time of VID was much longer than the rest. In component retention, MCD retained the higher content of polysaccharides, triterpenes and flavonoids, whereas, the VID effectively reduced the oxidation reaction and retained the polyphenols content in the vacuum environment. Meanwhile, the HAD group was obtained in the lowest contents of triterpenes and polysaccharides, due mainly to the long drying time of HAD and the high sensibility of components to heat transfer and oxidation. Therefore, the HAD drying was unsuitable for the retention of triterpenes and polysaccharides. In terms of energy consumption, the overall drying time of HAD and VID was relatively longer than the rest with low drying efficiency. The energy consumption of HAD and VID was much higher than that of AID and MCD. Among them, the VID took the maximum energy consumption of 88.32 kW·h/kg, while the MCD was the minimum energy consumption of 18.82 kW·h/kg. All indicators were firstly standardized in the IBM SPSS Statistics to obtain the data matrix, and then subsequent analysis was carried out. Two principal components were determined, according to the eigenvalue greater than 1.0. The cumulative contribution rate was set as 83.43%. The principal component analysis showed that the ranking was in the descending order of the MCD > AID > VID > HAD. The best quality was obtained in the MCD group, with the drying parameters at the humidity of 40% RH, and the moisturizing time of 15 min at 60 °C, where the comprehensive score was up to 2.94. This finding can provide some theoretical reference for the drying methods.