Studies of corn kernel steeping using microscopic NMR imaging

Abstract

Different MRI techniques were studied for the simultaneous and nondestructive measurement of transient moisture profiles and structural changes in corn kernels during steeping, including both Fourier transform and projection reconstruction imaging methods.

Temperature effects on MRI signals were analyzed. Each of the related MRI parameters ($\rho$, T$\sb1$, T$\sb2$, and D) need to be obtained as a function of temperature before one can fully explain the MR signals.

Chemical shift imaging techniques were studied to obtain the oil and water distribution inside corn kernels. The localized spectra and the water-only and oil-only images of a corn kernel were obtained with the SLIM4D sequence.

The gradient echo fast acquisition imaging technique was studied for the corn kernel-steepwater system. The outside steepwater was well suppressed and the inside structure of the corn kernel was revealed. T$\sb1$, T$\sb2\sp*,$ and proton density $(\rho)$ mapping were obtained. Water mobility and distribution inside the corn kernel during room temperature steeping were found. This technique gave acceptable performance for use in studying the corn-steepwater system.

Fast acquisition with an interleaved projection reconstruction imaging technique was studied for high resolution 3D data acquisition. Images of a corn kernel with 78 $\mu$m isotropic resolution were obtained in less than 10 minutes. The water surrounding the corn kernel was well suppressed. This technique proved to be very promising for studying dynamic processes.

An improved gradient echo Fourier imaging technique was used to study the corn steeping process. 3D transient moisture profiles and MR images of corn kernels were obtained during steeping with a range of different steeping conditions, such as with and without pericarp damage, high and low initial moisture content and drying temperature, with and without lactic acid, and high and low steeping temperature. The effects of these factors on each component of the corn kernel during steeping could be observed directly from 2D images, ROI images, contour images, image subtractions, and one- and two-dimensional moisture profiles produced from these images.