In the absence of defects, colour is one of the few practical criteria for assessing cucumber (Cucumis sativus L.) quality. However, cucumbers with the same colour at harvest can exhibit large differences in quality upon reaching the consumer. Photochemical yield (Φ(PSH)), photochemical quenching (q(p)) and a photosystem I. evaluation (k(c)), as internal quality measurements, were used in combination with an external quality measurement, represented by the colour, to test if the keeping quality could be predicted on the basis of these measurements. Keeping quality is defined as the time for a cucumber to reach a certain predefined colour limit. To test the hypothesis, colour changes for 2000 cucumbers were measured during storage at 20°C and 100% RH. The colour data were fitted to a model where a correction for biological age (C(ba)) was applied to each individual cucumber. The correction for biological age could be linked to the measured Φ(PSH), q(p) and k(c) values. Statistical analyses resulted in values for the maximum (green) and minimum colour (yellow) for each cucumber. The minimum colour could be correlated with different cultivars and the maximum colour with plant growing conditions. After a suitable transformation by a neural network, C(ba) could be estimated based on the values of Φ(PSH)s, q(p) and k(c) and the initial colour. Predictions on the keeping quality by the model resulted in an explained variance of 74% (R(adj)/2 = 0.74).
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