Studies on Citrus Carotenoids

Part IX. The effects of CPTA on the color development and the lycopene accumulation in Citrus Unshiu peel

Abstract

Effects of CPTA (2-(4-chlorophenylthio)-triethylamine hydrochloride) on the accelaration of coloring of Citrus Uhshiu was investigated. CPTA aqueous solutions were sprayed at the concentrations of 1250ppm, 2500ppm and 5000ppm on whole trees planted in porous pots.
All of CPTA treated ordinary Unshiu fruits developed bright red color and the appearance of treated fruits became to that of Dobashibeni-Unshiu. Determination of carotenoid groups of CPTA treated fruit peel by thin layer chromatography (TLC) showed the remarkable increase of hydrocarbon carotenoid group (H group) content. The maximum content of H group which was resulted from CPTA treatment of 2500ppm was 9 times as much as non-treated ones. The content of the other carotenoid groups showed no significant difference between CPTA treated samples and non-treated ones.
H group of CPTA treated fruit peel was subdivided into 6 fractions by alumina-TLC with petroleum ether as solvent. These fractions were identified and relative content was determined: F₁: β-carotene+ζ-carotene (6%), F₂: ζ-carotene (4%), F₃: γ-carotene (7%), F₄: -carotene (8%), F₅: Cis-lycopene (15%), F₆: lycopene (60%). In non-treated samples, only F₁ and F₂ fractions were contained. The color development of fruit peel by CPTA treatment seemed to be caused by the activation of lycopene biosynthesis pathway and lycopene content was accumulated to about 12% of the total carotenoids.