Analysis of the time course of core breakdown in 'Conference' pears by means of MRI and X-ray CT

Core breakdown in 'Conference' pears is a storage disorder, which is characterised by brown discolouration of the tissue and development of cavities. At the moment of purchase the consumer cannot detect these symptoms from the outside. In this paper magnetic resonance imaging (MRI) and X-ray computer tomography (X-ray CT) were applied to study non-destructively the time course of the disorder symptoms. Pears stored under disorder-inducing conditions were followed with both tomographic techniques during 6 months of controlled atmosphere storage. After 2 months, incipient browning could be detected with both techniques. However, the contrast between affected and unaffected tissue was higher on the MR images than on the X-ray CT scans. Two patterns of browning, radial and local, were observed. In the former, the contours of the brown tissue were concentric. Both patterns did not evolve or grow spatially over time, but only increased in their contrast to healthy tissue during storage. This result suggests a relation between the disorder and gas exchange properties of the fruit with the environment. It was also observed that the cavities grow at the expense of the brown tissue. To quantify the browning rate a contrast value was defined based on the ratio of pixel intensities of affected and unaffected tissue. The average browning rate did not differ substantially between the different pears and was equal to 0.0065 +/- 0.0005 days (-1) (C) 2002 Elsevier Science B.V. All rights reserved.