不同干燥方式对红托竹荪干燥特性和品质的影响

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

为提高红托竹荪干燥品质并获得最佳干燥工艺,采用真空红外干燥(vacuum infrared drying,VID)、气流冲击干燥(air impingement drying,AID)、控湿干燥(moisture control drying,MCD)等不同干燥方式对红托竹荪进行对比研究,以热风干燥(hot air drying,HAD)作为对照组,研究不同干燥方式及温度对红托竹荪干燥品质的影响。试验结果表明不同干燥方式对竹荪宏观品质产生了显著影响,其中MCD可获得最小的色差∆E和收缩率,AID则能够保证较高的复水比;干燥速率方面,MCD在前期能够获得较高的干燥速率,但后期干燥速率会放缓,而AID在整个干燥过程都具有较高的干燥速率,干燥时间较短;在成分保留上,MCD可以保留较高含量的多糖、三萜和黄酮,而采用VID可以有效保护多酚。单位能耗随干燥温度的升高明显降低,不同方式下VID的干燥能耗值整体偏大,MCD的单位能耗最低(18.82 kW·h/kg)。通过主成分分析法,上述干燥方式对红托竹荪综合评分后得到的结果排序为:MCD>AID>VID>HAD,MCD干燥方式中采用60℃相对湿度为40%,保湿时间15min的干燥工艺综合品质较佳,在此加工方式下的红托竹荪综合评分为2.94,该研究可为红托竹荪高品质干燥提供一定参考。

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 lowΔE 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 1440 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.