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Dissertation
X-ray CT to detect internal structures in apple fruit : From high-resolution 3D microstructure imaging towards fast screening tools
Authors: --- --- --- ---
Year: 2014 Publisher: Leuven KU Leuven. Faculteit bio-ingenieurswetenschappen

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Abstract

Pome fruit is often stored up to 10 months at a low temperature (-0.5 ° C to 3 ° C), in combination with reduced O2 and elevated CO2 partial pressures. Storage at low temperature, combined with 'Controlled Atmosphere' (CA) is used to reduce the respiration activity of the fruit thereby minimising the associated quality changes, and thus extending the storage time. The gas composition is of great importance as physiological defects like internal browning and void formation can occur at suboptimal conditions. Also during the growth phase, various defects can occur, as watercore in apple with hard, glassy zones near the core. A major problem is that these symptoms are not externally observable, and affected fruit cannot be easily distinguished from healthy. Internal fruit quality is typically evaluated based on visual inspection of a randomly selected sample of fruit. Only after cutting the fruit, and thus destroying it, an assessment can be made. When the sampled fruit are affected, the whole batch is rejected and destroyed. The scientific objective of this research project is a better understanding of the development of the symptoms of internal defects in apple and pear. The technological objective is the development of a non-destructive and rapid image-based method for evaluating internal fruit quality. This should lead to a better sorting of fruit with less losses in the sector and a high, uniform fruit quality on the market as a result. Fruit of Braeburn, Kanzi and Conference were stored under defect-inducing CA conditions through which internally brown and hollow fruit were successfully obtained. Cultivars Ascara, Tempera, Rebellón and Verde doncella were delivered from Spain, where a higher risk of watercore is present because of the climatic conditions. These internal defects are generally characterised by a change in density of the affected tissue. Previous research has shown that X-ray radiography and tomography are particularly suited to detect these internal problems both at the micro- and macroscale. With the help of X-ray micro-CT a large number of fruit samples was scanned such that a complete characterisation of these physiological defects was obtained, in different stages of development, for the different cultivars. Preliminary tests on the whole fruit with X-ray radiography and CT have shown that these technologies are able to detect quality defects in different gradations. Additional high-resolution micro-CT measurements will be performed on tissue pear to complete the microstructural evaluation of internal quality. In an extensive experiment, large numbers of affected and non-affected fruit are scanned so that the detection success of X-ray CT and radiography can be assessed. By fine-tuning measurement conditions and optimise the imaging and processing, this should ultimately lead to the development of a test rig in which affected and healthy fruit are sorted on-line, based on the internal fruit quality.

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