Optimisation of non-invasive optical and thermic imaging techniques in the assessment of the quality of apples and of its storage potential

At present, most of the techniques used to assess the quality of all individual products for internal quality conditions such as firmness, sugar, starch and aroma are destructive.  Quality assessment by non-destructive technologies can be performed by optical and thermal methods.  These are based on the detection of various physical properties, which correlate well with certain quality factors of the apple.  Optical methods which utilise high-speed optical detection and computerised data-processing, such as the in vivo fluorescence imaging and near-infrared reflectance spectroscopy are successful methods which can provide high-speed quality evaluation and sorting of several products with a high degree of accuracy.  The fluorescence imaging technique is based on the time dependant fluorescence emission (in the red and far-red region of the spectrum) of the photosynthetic chlorophyll molecules by excitation with blue light.  This time dependency reflects the capacity of the photosynthetic electron transport and consequently of the physiological status of the plant organ.  Compared to currently used fluorescence methods, which are essentially based on point measurements, the fluorescence imaging techniques takes the fluorescence emission of a whole leaf or fruit.  This technique is used at the laboratory at Limburgs Universitair Centrum to study fruit quality. It was tested under South Africa conditions during the passed two seasons and preliminary results showed a possibility of identifying pre-harvest bitter pit potential. NIR-reflectance is being used in a number of field crops.  This technique is also used to determine soluble solids, which are related to sweetness, aromatic substances and taste in apple and pear fruit.   This technology is currently further developed at the ‘Flanders Centre for Post Harvest Technology’ in Leuven. Results from point readings using NIR spectroscopy indicated that it is not suitable for early identification of bitter pit due to the fairly local expression of this disorder.