The CIELab colour system is used to evaluate food colours. Its advantage is that the base skin colour of bicoloured apples can be measured on the same fruit before and on the optimum harvest date. Additionally, it makes it possible to take many measurements within a short time. The changes of skin colour (yellowing) are caused by chlorophyll degradation. During fruit development and maturation chlorophyll breakdown is observed, which results in decreasing intensity of green coloration. The aim of the five-year study was to evaluate a fast and non-destructive method of determining the optimum harvest date of apples intended for long storage based on changes observed in the base skin colour. Apples of ‘Ligol’ and ‘Jonagored’ cultivars were collected every 4–5 days starting some weeks before the estimated OHD. On the last four or five sampling dates in all years of the study, apples were collected for cold storage. The storability of apples was evaluated after the same number of days of storage respectively to their harvest date. Storage efficiency was evaluated based on judgment that involved sensoric tests and checking of the incidence of diseases and disorders in apples, as well as on measurement of fruit mass loss and internal qualities (firmness, TSS, TA). From among the evaluated colour indicators L*, a*, b*, Hue_ab angle and chroma, changes in the base colour were best illustrated by the a* coordinate value and the Hue_ab angle value. Based on the evaluation of the quality of apples after storage, it can be stated that the apples had the best quality when the a* coordinate during harvest ranged between -13.5 and -15.5 for ‘Ligol’ and between -4.9 and -5.7 for ‘Jonagored’. The Hue_ab angle assumed a value between 107 and 109 for ‘Ligol’ and between 98 and 99 for ‘Jonagored’ during the optimum harvest date. Therefore, the a* coordinate and the Hue_ab angle can be used as indicators of harvest maturity.

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