Cottonseed oil estimation by pulsed nuclear magnetic resonance technique

Seed asymmetry and moisture associated with the seeds are known to affect seed oil estimation by pulsed nuclear magnetic resonance (NMR) technique employing free induction decay or single spin echo (SE) pulse sequence. UsingGossypium (cottonseeds) as experimental material, it is shown that transverse relaxation times (T₂) of seed oil, in different varieties of seeds, measured in vivo, are not the same. The mean T₂ value of tetraploid seeds is found to be significantly higher than that of diploids. The effect of T₂ variation and other problems on oil estimation by the free induction decay and SE methods can be avoided by using the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence to monitor the signal intensities of a certain number of selected echoes and processing them to yield the extrapolated signal intensity at zero time. The oil content values thus estimated are found to agree well with those obtained by Soxhlet method. The agreement between the two methods might depend upon the presence of gossypol and other pigments present in the samples. Neither delinting nor dehydrating the seeds is necessary in the present method. Even with the CPMG sequence, use of individual echoes is not recommended, as the T₂ variations give rise to erroneous values.