Magnetic resonance imaging and relaxometry to visualize internal freeze damage to pickling cucumber

Magnetic resonance (MR) images and tissue relaxometry (T1 and T2) data, using a 9.4 T MR system, were used to assess freeze damage to pickling cucumbers. Freeze damage was induced by placing cucumbers at −18 °C for 150 min and the samples were then stored in a controlled atmosphere. T1 and T2-weighted images were generated at echo time (TE) of 10 ms at specific intervals for cucumbers stored for a period of 7 d. Texture profile analysis of the control and freeze-damaged samples was also carried out on the day of MR imaging. MR images showed good contrast between different physiological constituents of a pickling cucumber. A subsurface region in the freeze damaged samples was distinctly different in all MR images which could be physically correlated with damaged tissues visible in a cut-away section of the freeze-damaged pickling cucumber. Spin–lattice relaxation time (T1) was not different for different constituents of a pickling cucumber and could not be used to resolve between control and freeze damaged samples. Whereas, spin–spin relaxation time (T2) values for all the regions of a cucumber slice were higher for the freeze-damaged samples than that for control samples. The T2 values for seeds and the gel around seeds sections were also significantly different from the rest of the cucumber constituents. However, T2 values did not change significantly over the storage period. Firmness and chewiness characteristics of pickling cucumbers changed during the storage; however, there was no correlation seen between T2 values and firmness of the fruit.

► Subsurface freezing damage to cucumbers was viewed using MRI and tissue relaxometry.
► Images showed good contrast among different constituents of a cucumber.
► T2 values of a cucumber slice were higher for the freeze-damaged samples.
► T2 values did not change significantly over the 7 d storage period.
► There was no correlation seen between T2 values and firmness of the fruit.