Thermographic surface quality evaluation of apple
2006
Veraverbeke, E.A. | Verboven, P. | Lammertyn, J. | Cronje, P. | De Baerdemaeker, J. | Nicolai, B.M.
Thermographic IR-imaging was used as a non-destructive tool to evaluate the surface quality of apples. Experiments were carried out on apple fruit of two different cultivars (Jonagored and Elshof) picked at two different picking dates (early and late). First, the emissivity of the apple skin was determined as 0.96 for both cultivars. Next, recordings were made of individual fruit of both cultivars cooled from 20 degrees C to 12 degrees C. In this experiment Elshof apples had a faster cooling rate and lower temperature than Jonagored apples. Finally, a storage experiment was carried out under standardised conditions with quality assessment after 4 and 8 months of CA storage and at each storage period after 0, 1, and 2 weeks of shelf life. Next to the determination of general quality parameters (weight, diameter), thermographic images of the surface of each apple were obtained. Temperature profiles were recorded for batches of four fruits and of all individual fruit within this batch while they were cooled from 12 degrees C to 1 degrees C. The surface cooling rate and final fruit surface temperature were estimated. All data were calibrated for background temperature and corrected for apple dimensions and convection coefficients. ANOVA analysis showed significant differences between both cultivars, picking dates and storage conditions for the cooling rate. The final surface temperature differed significantly between different storage and shelf life periods. Only the difference in cooling rate with a faster cooling for Elshof than for Jonagored was explained in terms of wax structural characteristics and transpiration rates. The results also show the importance of data correction.
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