Moisture phase state and distribution characteristics of seed during rice seed soaking process by low field nuclear magnetic resonance

Nuclear magnetic resonance(NMR) is a fast, nondestructive and accurate test technique, which can be used to study the phase and distribution characteristics of moisture in rice seed during the soaking process.In this paper, the transverse relaxation time T2 has been analyzed by Carr Purcell Mei boom Gill(CPMG) pulse sequence.Thephase and change rules of moisture in rice seed are distinguished according to the different transverse relaxation time T2 in the T2 inversion spectrum.Samples of rice seed(variety was Shennong 9903)were obtained from Rice Research Institution, Shenyang Agricultural University in 2014.The mass of 10 seeds was determined as one sample with the total weight of 0.251 g, and there were 120 samples that were used in the present paper.The central frequency and the width of pulse of the magnetic field were searched by free induction decay(FID) pulse sequence, and all test samples were put in the low field NMR instrument one by one.All the tests were conducted by 4 times.The initial moisture content of the seeds was analyzed by NMR and the average transverse relaxation time T2 of rice seed was determined by CPMG pulse sequence.Test samples after data acquisition were soaked in water; the soaking time was ranging from 1 to 6h under standard laboratory conditions(20 ℃).After wiping the surface water of test samples with absorbent paper, the soaked samples were put in the NMR instrument again for data collection, and each test was repeated by 4 times.The spin echo signals collected by the repeated tests were valuated by the NMR inversion fitting software, and the average value of the inversion results was taken as the relaxation time and the signal amplitude of the sample.All the experimental data were statistically analyzed and expressed by mean ± standard deviation, and the results were analyzed by the regression analysis.The comparative dispersion of the data were obliterated according to the composition of the samples, the NMR equipment and the different measurement parameters.The test results showed that the low field NMR technique could be used for the analysis of the component,distribution and content of rice seed moisture during the soaking process.The results also showed that the value of T2 could indicate moisture component and phase state and the value of moisture signal amplitude(A2) could reflect the distribution of moisture.Moisture stratification and phase state could be evaluated by changing the number of iterations in the inversion fitting procedures.The experimental results showed that: the internal moisture of seed could be divided to bound water and free water during the soaking process according to the different transverse relaxation time T2.Moisture stratification of seed could also be divided into inner moisture, middle moisture and outer moisture.It could be seen that the moisture absorption ratio of rice seed could be reasonably estimated by the regression equation of 2 moisture states and moisture stratification.It was found that the total moisture content was kept increasing in the soaking process according to the difference of signal amplitude in the T2 inversion spectrum, while the movement of moisture was a little different due to different determination basisand classification.Low field NMR technique has 2 advantages: the first one is it reveals the moisture variation more intuitively during seed soaking, the second one is itreveals the moisture transfer more dynamically during seed soaking, and thus it provides an efficient detection method for the determination of the moisture content of seeds.