Analysis of moisture changes during rice seed soaking process using low-field NMR

Low field nuclear magnetic resonance (LF-NMR) has the technique advantages of nondestructive and non-invasive, which can be used to study the variation, distribution and flow of different phase state moisture in rice seed through the detection of proton's density and distribution in samples. In this paper, Shennong No. 9816 and No. 9903 rice seeds were used in the study. The center frequency and pulse width were determined using the FID pulse sequence in the NMR spectroscopic analysis software. The low field NMR technique and dynamic detection of the CPMG pulse sequence signal were used to determine the spin relaxation time of samples (the transverse relaxation time T2). The variation and flow of different phase state moisture during seed soaking were analyzed by the change of time signal and the peak position due to the inversion mapping of T2. The value of the relaxation time T2 reflected the value of the water degree of freedom in the sample. The change of the relaxation time T2 can reflect the mobility of the water molecules. The effects of rice varieties and soaking temperature on the moisture absorption ratio has been studied according to the regression equation between the T2 relaxation spectrum total area of peak A and rice seed moisture absorption ratio. The experimental results showed that the regression equation of the T2 relaxation spectrum peak area and the moisture absorption ratio of rice seed was correlated well and the equation reached a significant (P 2 relaxation spectrum peak area. The moisture in the rice seeds was in two phases, combined moisture and free moisture during soaking process according to the multiple components characteristics of T2 and moisture characteristics of the seed. The critical value of combined moisture and free moisture was 10 ms. The short relaxation time T21 (0.1-10 ms) was defined as combined moisture. This water was closely linked to protein, sugar, phospholipids and other through hydrogen bonds. This water can not flow freely and evaporate. The longer relaxation time T22 (10-1000 ms) was defined as free moisture in magnetic field. This water was in the vacuole, the intercellular and cells gap, which can not be absorbed by the colloid or with poor adsorption capacity. This water can flow freely and can be used as solvent since it has the general properties of water. As for Shennong No. 9816, the trends of combined moisture and total moisture content kept increasing, while the variation of free moisture content was irregular during 18℃ and 6 h soaking process. The variation of moisture content can reflect the physical and chemical reactions in rice seed during soaking process. The differences of rice seed moisture absorption in two rice cultivars were not significant (P>0.05), but rice seed moisture absorption was highly sensitive to the soaking temperature. With the increased soaking temperature, the rice seed moisture absorption per unit time significantly (P ©, 2015, Chinese Society of Agricultural Engineering. All right reserved.