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Thermographic surface quality evaluation of apple

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  036207,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.15337)
Authors:   Els A. Veraverbeke, Pieter Verboven, Jeroen Lammertyn, Paul Cronje, Josse De Baerdemaeker, Bart Nicolaï
Keywords:   apples, wax, quality, water loss, thermography

Thermographic IR-imaging was used as a non-destructive tool to evaluate the surface quality of apples. Surface quality determines both the consumer visual appreciation and cuticular moisture loss during storage. 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 and set to 0.96 for both cultivars. Next, recordings were made of the cooling from 20C to 12C of individual fruit of both cultivars for which Elshof had a faster cooling rate and lower temperature than Jonagored. 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), also thermographic images of the surface of each apple were obtained. Temperature profiles were recorded of batches of four fruit and of all individual fruit within this batch while they were cooled from 12C to 1C, and 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 among 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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