基于低场核磁共振的热风干燥过程花生仁含水率预测模型

Prediction model of moisture in peanut kernel during hot air drying based on LF-NMR technology

为研究热风干燥过程中花生仁内部水分的变化规律,该文采用热空气对开农71、开农8834-9、天府3号3个品种的湿花生进行干燥,监测干燥过程中花生果、花生仁与花生壳含水率的变化;并利用低场核磁共振技术(LF-NMR)研究干燥过程中花生仁内部自由水、弱结合水和结合水的变化情况;建立花生仁水分弛豫峰占比与其含水率之间的数学关系,提出了一种花生含水率的快速检测方法。结果表明,由于花生仁和花生壳化学组成不同,仁和壳干燥曲线呈现不同的变化趋势。LF-NMR弛豫图谱显示干燥过程中,自由水弛豫峰逐渐消失,结合水和弱结合水弛豫峰面积无明显变化规律,油脂峰峰面积基本不变,说明花生仁在干燥过程中油脂的含量无明显变化。建立的花生仁国标法实测含水率y与核磁共振弛豫谱图得到的总水分峰占比(T21+T22+T23)的拟合方程R2为0.888 4。经验证,该方程能较好地对未知含水率的花生仁样品进行预测。因此,低场核磁共振技术可以用于花生仁含水率的快速检测。

Peanut,which has high economic value,is one of the main oil crops in China.Freshly harvested peanuts usually had high moisture contents,which were about 40%-60%.If peanuts with high moisture content did not dry in time,it was easy to fever and mildew.So it is very important for peanuts drying in time.In this paper,three varieties of wet peanuts,Kainong 71,Kainong 8834-9 and Tianfu 3,were dried by hot air,which temperature was 35℃and air velocity was 0.6 m/s.And the moisture contents of peanuts,peanut kernels and peanut shells were monitored during the drying process.The changes of free water,weak-bound water and bound water in peanut kernels during drying were studied by low-field nuclear magnetic resonance(LF-NMR)technology.The common law of internal moisture changes in peanut kernels during drying process was obtained.The mathematical relationship between the total percentage of moisture relaxation peaks in peanut kernels and their moisture contents determined by the national standard method was established.A rapid detection method of peanut moisture contents was proposed in this paper,which had a practical significance for peanut storage and processing.The results showed that regardless of the amount of oleic acid in peanuts and the size of the peanuts,the drying characteristics of the three varieties of peanuts were similar.The moisture contents of the three varieties of peanut and peanut kernel showed different downward trend compared to the peanut shell.The moisture contents of peanut shell first declined rapidly in the early stage(2-4 h),then slowly due to their fiber structure.The LF-NMR relaxation spectra of peanut kernels of the three varieties all had four main peaks,namely,free water peak,weak-bound water peak,bound water peak and oil peak.During the drying process,the free water peak areas of peanut kernels of the three varieties decreased gradually,and almost disappeared at the end of drying.The changing trends of the weak-bound water and bound water peak areas were obvious.The peak areas of oil peaks did not change significantly,indicating that the oil content in peanut kernels remained unchanged during drying process.The relaxation peak area ratios of peanut kernels of the three varieties in low-field NMR relaxation spectra also showed similar trends during drying.The percentages of bound water peak area and oil peak area showed an upward trend.The percentage of free water peak area showed a downward trend,which was very low at the end of drying,indicating that free water almost completely lost at the end of drying.The percentage of weak-bound water peak area firstly rose,then declined at the end of drying,indicating that some weak-bound water was lost.Therefore,free water and weak-bound water were the main kind lost water in the drying process.In addition,it could be judged that if the relaxation peak of free water disappeared or the peak was very small,the moisture contents of peanut kernels were below the safe storage moisture content.The R 2 of equation established to predict the moisture content of peanut kernel is 0.888 4.The equation has been validated and the fitting results were good.Therefore,the LF-NMR technology can be used for rapid detection of moisture content in peanut kernels.