Moisture content in midrib of tobacco leaves during flue-curing as determined by LF-NMR

In order to study the moisture variations in midrib of tobacco leaves during flue-curing, low-field nuclear magnetic resonance(LF-NMR) was used to determine the content and state of moisture, and the results were compared with those determined by a conventional oven method. The results showed that: 1) The moisture in midrib of fresh green tobacco leaves included bound water T₂₁(1-10 ms) and free water T₂₂(100-1 000 ms). During flue-curing, the signal amplitude of free water M₂₂ and total water M₂₀ decreased, and the signal amplitude of bound water M₂₁ increased first then decreased. 2) Linear regression analysis indicated that the total signal amplitude of inversion spectrum positively correlated to the moisture content and dry weight base moisture content at a significant degree (coefficient of determination R²=0.997 9, R²=0.998 3, P＜0.01). The moisture content in leaves during flue-curing could be obtained by the regression equation obtained. 3) Comparing with the oven method, the stability of LF-NMR was better. LF-NMR is thus suitable for the rapid and accurate determination of moisture contents in midrib of tobacco leaves during flue-curing.