Abstract: Developmental changes in the content and composition of pigments, especially carotenoids, in Citrus iyo Hort. ex Tanaka cv. Miyauchi fruit and their correlations with fruit coloration were studied. High content of chlorophylls in young fruit was responsible for its green color. Intensive increase in content of carotenoids and rapid loss of chlorophylls commenced at 8 and 4 weeks before harvest respectively, and both changes contributed to yellow color development in ripening fruit. 83.62% of total fruit carotenoidswas found located in the peel, where carotenoid content was 16.62 times as high as that in the pulp. Composition of carotenoids in the peel within 12 weeks before fruit harvest was analyzed using high performance liquid chromatography-photodiode array detection (HPLC - PDAD). 23 carotenoids were separated and 7 of them were identified. Among identified carotenoids, β-cryptoxanthin and zeaxanthin were relatively abundant and accounted for 8.00% and 6.78% of total carotenoids respectively; β-carotene was less than 1% of total while α-carotene and lycopene were undetectable. The increase in content of β-cryptoxanthin and zeaxanthin was accompanied by the decrease in content of lutein, α-carotene andβ-carotene during late fruit development, indicating that
carotenoid β pathway and β-ring hydroxylation activities were enhanced. Meanwhile, the appearance and accumulation of apo-carotenoids suggested an increase in carotenoid cleavage activities as the fruit ripened.

Key words: Citrus iyo, External fruit color, Carotenoids, Pigments