基于低场核磁和电镜扫描法对热风干燥花生仁的水分状态研究

Study on moisture state of peanut kernel dried by hot air based on low field NMR and SEM

为研究花生仁热风干燥过程中内部水分分布状态及变化情况,采用低场核磁共振技术,测定花生仁在不同热风干燥温度(35、40、45、50、55℃)下的横向弛豫时间反演谱,并利用扫描电镜观察干燥过程中花生仁微观结构变化。研究表明:花生仁在热风干燥过程中,干燥速率前期随着干燥温度的上升而显著提高,后期受影响较小。因此最佳干燥条件为干燥温度55℃、4h后,降低干燥温度为35~40℃至干燥终点。LF-NMR横向弛豫图谱显示干燥过程中自由水峰和弱结合水峰面积显著下降,结合水峰面积基本不变。将35、40、45、50、55℃干燥过程中的水分总峰面积与花生仁的干基含水率进行回归分析,R2均大于0.986,具有较高的拟合度。拟合方程可用于预测热风干燥过程中水分状态与花生仁干基含水率的关系。

In order to study the internal moisture distribution and changes of peanut kernels during hot-air drying, low-field nuclear magnetic resonance(LF-NMR) technology was used to determine the inversion spectrum of transverse relaxation time of peanut kernels at different hot-air drying temperatures(35, 40, 45, 50 ℃ and 55 ℃). The microstructure changes of peanut kernels during drying were observed by scanning electron microscope(SEM). The research indicated that during hot air drying of peanut kernels, the drying rate increased significantly in the early stage with the increase of drying temperature, and the effect was small in the later stage. Therefore, the optimal drying conditions were the drying temperature of 55 ℃, after 4 hours, and then, the drying temperature was 35~40 ℃ and reduced to the drying end point.The LF-NMR transverse relaxation spectrum indicated that the areas of free water peaks and weakly bound water peaks decreased significantly during the drying process, while the bound water peak areas remained basically unchanged. The regression analysis of the total moisture peak area and the dry basis moisture content of peanut kernels in the drying process at 35, 40, 45, 50 ℃ and 55 ℃ showed that R~2 was greater than 0.986, indicating a high degree of fit. The fitting equation could be used to predict the relationship between the moisture state and the dry basis moisture content of peanut kernels during hot air drying.