Using MRI to Study High Pressure Assisted Nutrient Infusion

Abstract

High pressure assisted infusion of nutrients into food was in situ monitored with magnetic resonance imaging (MRI). Modification of an off-the-shelf pressure reactor with an MRI detection circuit provided a large enough volume to accommodate food. The model food used here was peeled apple flesh as it is considered as a good mimic for fibrous food. The nuclear spin relaxation properties of the water surrounding the apple flesh were enhanced by adding paramagnetic manganese cations. In this way, MRI relaxation contrast can be used to monitor the location of doped bulk water in and around the apple flesh during pressurization. This work tracked the efficiency of pressure induced nutrient infusion in situ, demonstrating that pressure gating and ramping offer no nutrient mass transport advantage over operation at constant pressure and that the presence of a peel expectedly disrupts solute transport into the fruit. High pressure assisted infusion, with all pressurization strategies shown here, yielded nearly 100-fold faster infusion times than at ambient pressure.

Keywords: MRI; diffusion; high pressure; high pressure assisted infusion.

Figure 1

Timing diagram comparing the static 80 MPa pressure in (a), cycled 20 MPa pressure in (b), static 20 MPa pressure in (c), ramped pressure up to 80 MPa in (d), and ambient pressure in (e) pressurization strategies. Each pressurization run typically lasted 4.5 h while the pressure changes indicated in the diagram, which included a 5 min equilibration period, lasted roughly 10 min.

Figure 2

The graphics on the left are illustrative and can be used to understand the real MRI data shown on the right. The real MRI data on the right in (a–c) were obtained at time 0 prior to pressurization. The data on the right of (d) was taken at 80 MPa after 140 min of pressurization. The top and side views of a cubic apple section are described in (a,b) by the gray solid box on the left and in the corresponding dark squares in the right column images. The white region in these 2D diagrams in both columns corresponds to the bulk doped solution outside the cubic apple section. The 1D slices shown in (c,d) were obtained at the location of the white dashed line in the left (b) image. The gray box bounded by small arrows on the right-hand side of (c,d) indicates the image region where Equation (1) is valid while the solid gray box defines the range 0 < α < 1 in Equation (2). The arrows are included to specify the box boundary.

Figure 3

The illustrative 1D slices on the left can be used to understand the real MRI data on the right obtained at 80 MPa applied external pressure. The peel is located at −4 mm, denoted by the dotted line, in all images. The 1D image at 40 min into the pressure run in (a) appears to fill in from the side opposite the peel in (b) obtained after 160 min at pressure.