A new method developed to characterize the 3D microstructure of frozen apple using X-ray micro-CT

Non-destructive imaging techniques have become indispensable to improve insights into the micro structural changes occurring in fruit tissue during freezing. Here, apple cortex tissue samples were frozen using different freezing rates: (i) slow freezing (2.0 degrees C per min.), (ii) intermediate freezing (12.6 degrees C per min.) and fast freezing (18.5 degrees C per min.). Temperature-controlled X-ray micro-CT was optimized and then applied to visualize and quantify the 3D microstructure and ice crystal distribution at a pixel resolution of 3.8 mu m. Ice crystal size distributions with mean equivalent diameters of about 41 +/- 3.5 mu m, 55 +/- 7.4 mu m and 71 +/- 9.6 mu m were obtained for the fast, intermediate and slow freezing rates, respectively. A new imaging methodology was developed and validated to allow segmentation of the ice crystals in frozen apple tissue using the X-ray attenuation coefficients of the reference model samples, i.e. frozen pure water and concentrated apple juice. (C) 2017 Elsevier Ltd. All rights reserved.