利用低场核磁共振分析水稻种子浸泡过程中的水分变化

摘要

为研究水稻种子在浸泡过程中的水分变化情况，应用核磁共振无损、非侵入的技术优势，根据弛豫时间呈现的多组份特征，通过弛豫谱分析水稻种子不同相态水分的变化和流动过程，确定弛豫谱峰值总面积与水稻种子吸水率的回归方程，研究了水稻品种（沈农9816号、沈农9903号）及浸种温度（18、24、32℃）对水稻种子吸水量的影响。试验结果表明：通过弛豫谱峰值总面积可以合理估测水稻种子的吸水率；水稻种子在6h浸种过程中，随着浸泡时间的增加结合水及总水含量变化趋势为不断上升，自由水则呈现不规则的反复变化态势；水稻种子吸水量在2个水稻品种间差异不明显，对浸种温度高度敏感。该试验提出了一种无损的水分检测方法，能够更加直接准确的揭示水稻种子在浸泡过程中的水分变化规律，为探求种子的最佳浸泡条件提供数据支持和理论依据。%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 timeT2). 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 ofT2. The value of the relaxation timeT2 reflected the value of the water degree of freedom in the sample. The change of the relaxation timeT2 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 theT2 relaxation spectrum total area of peakA and rice seed moisture absorption ratio. The experimental results showed that the regression equation of theT2relaxation spectrum peak area and the moisture absorption ratio of rice seed was correlated well and the equation reached a significant (P < 0.05) level of detection. The moisture absorption ratio of rice seed was reasonably estimated through theT2relaxation 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 ofT2 and moisture characteristics of the seed. The critical value of combined moisture and free moisture was 10 ms. The short relaxation timeT21 (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 timeT22(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< 0.05) increased. This experiment proposed a non-destructive rice seed moisture content detection method, which can reveal the moisture variation more directly and accurately during seed soaking, thus the results can be used to determine the best soaking conditions.