Orange Colour Formation and Pigment Variation on Tropical Tangerine Peel by Precooling and Degreening

Background and Objective: Tropical tangerine (Citrus nobilis Lour) can not produce orange peel colour naturally due to the absence of low temperature during the pre-harvest condition. This study aimed to evaluate the effect of precooling and ethylene application on degreening and variation in pigment metabolites (chlorophyll, $-carotene, $-cryptoxanthin and zeaxanthin) of the tropical tangerine peel. Materials and Methods: Approximately 960 fruits of low land tropical tangerine were subjected to precooling and various ethylene concentrations (0, 100, 200 and 300 ppm) for degreening. Results: The result showed that both precooling and degreening induced peel colour alteration of tangerine fruit, from green to yellow and yellowish-orange. In general, chromaticity analysis resulted in the increase
of the Citrus colour index and the decrease of Ehue after 10 days of storage. The best treatment for the best colour (yellowish orange) achieved was the combination of precooling and degreening with100 ppm ethylene. The colour transformation was also proved by the quantitative change of chlorophyll and carotenoid ($-carotene, $-cryptoxanthin and zeaxanthin) that revealed by reverse-phase highperformance liquid chromatography. Conclusion: Both chlorophyll and $-carotene were significantly reduced in fruit treated by best
treatment, while the $-cryptoxanthin showed a significant and multi-fold increased, ascertained by the formation of strong yellowishorange peel colour within this treatment. The effect of a single factor either only precooling or degreening was less powerful than the best combination treatment.