低场核磁共振技术在稻谷水分测定中的应用

Application of Low Field Nuclear Magnetic Resonance(LF-NMR)in the Determination of Rice Moisture

低场核磁共振法作为新兴的种子水分检测方法,具有简便、快速、无损等优点,此外还可实现单粒种子成像。本文以新峰6号香、龙粳40、吉宏、超级稻、盐丰、桥育等6种稻谷为试验原料,使用低场核磁共振仪器建立了低场核磁水分标准曲线,标准曲线线性良好,相关系数大于0.99,验证结果为国标法测定的水分与低场核磁共振技术法测定的水分差在0.2%以内,可以认为在19~25℃的范围内,低场核磁共振技术适合测定高水分到低水分稻谷的水分。试验发现,国标法测定水分,2次恒重后水分仍会下降,若延长恒重的间隔时间,2次测定重量差值会超过2 mg,烘干终点很难判断,因此推测国标法测定的水分并不是样品水分的真值。本文同时研究了稻谷整粒方式和不同粉碎方式对水分测定的影响以及立式粉碎的时间、整粒烘干的时间对水分测定的影响,以期对稻谷真值水分进行探索,也为低场核磁共振技术更加合理准确的水分测定和验证提供指导,利于后期进一步的开发应用。结果发现稻谷整粒测定的水分低于立式粉碎后稻谷测定水分,表明粉碎会改变稻谷的结合水与自由水比例;不同立式粉碎时间的稻谷,随着粉碎时间增加,结合水先增加后降低,自由水逐渐降低;单独依靠烘箱测定水分,通过延长烘干时间并不能得到稻谷真值水分。

As a new seed moisture detection method,low field NMR has the advantages of simplicity,rapidity and non-destructive,and can realize single seed imaging.In this paper,six kinds of rice such as Xinfeng 6 Xiang,Longjing 40,Jihong,super rice,Yanfeng and Qiaoyu were used as experimental raw materials,and the low field NMR water standard curve was established by using the low field NMR instrument.The standard curve has good linearity and the correlation coefficient is greater than 0.99.The verification result is that the difference between the water measured by the national standard method and the water measured by the low field NMR method is within 0.2%,which can be considered to be in the range of 19~25℃,Low field NMR is suitable for the determination of water content in rice from high water content to low water content.During the experiment,it is found that the moisture measured by the national standard method will still decrease after two constant weights.If the interval between constant weights is prolonged,the weight difference between the two measurements will exceed 2 mg,and it is difficult to judge the drying end point.Therefore,it is speculated that the moisture measured by the national standard method is not the true value of the sample moisture.At the same time,this paper studies the effects of whole grain and different crushing methods on moisture measurement,as well as the effects of vertical crushing time and whole grain drying time on moisture measurement,in order to explore the true value moisture of rice,and also provide guidance for more reasonable and accurate moisture measurement and verification of low field NMR technology,which is conducive to further development and application in the later stage.The results showed that the water content of whole rice was lower than that of rice after vertical crushing,indicating that crushing would change the ratio of bound water to free water;with the increase of milling time,the bound water first increased and then decreased,and the free water gradually decreased;the true moisture of rice can not be obtained by prolonging the drying time.