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Effect of High Temperature on Carotenoid Composition of Bitter Gourd (Momordica Charantia L.) Fruits
Thesis Abstract:
Detached mature green bitter gourd (Momordica charantia L.) fruits of the “Jade Star X” variety, were held at 25°C and 35° C to re-examine the carotenoid distribution in bitter gourd fruits at different maturities and also to study the effect of high temperature on carotenoid composition in the pericarp and the aril during the ripening process. Zero, two, four, six and eight days after harvest, the pericarp and aril of bitter gourd fruits were analyzed for carotenoid composition.
Carotenoid content of bitter gourd fruits obviously changed with maturity. At the mature green stage, only six carotenoids were isolated in the pericarp. They are α-carotene, β-carotene, α-cryptoxanthin, lutein, isolutein, and anthraxanthin. As soon as fruits turned yellow, the principal pigments of mature green stage, lutein and isolutein, disappeared, and β-cryptoxanthin, zeaxanthin and violaxanthin accumulated rapidly. At the same time, α-carotene and α-cryptoxanthin concentrations decreased while β-carotene content slightly increased without significant difference. The total carotenoid content of the pericarp at fully ripen stage was almost double the content at mature green stage.
In the aril, although the number of carotenoids did not change, the concentration of each pigment, especially lycopene, increased significantly with ripening. Therefore, the total carotenoid content rose from an average of 18.66 μg/g dry wt at mature green stage to an average of 551.2 μg/g dry wt at fully ripen stage. Lycopene was the major pigment and responsible for the red color of aril at ripening stages. In addition, α-cryptoxanthin and β-cryptoxanthin were also detected in the aril.
Effect of high temperature on carotenoid composition of bitter gourd pericarp was observed in the acceleration of color development in the pericarp of fruits held at 35°C as a result of earlier accumulation of β-cryptoxanthin and zeaxanthin accompanying earlier degradation of lutein and isolutein. Lycopene was not detected in the pericarp at any time during ripening.
In the aril of bitter gourd fruits, high storage temperature 35°C caused partial inhibition of lycopene accumulation. There was no red color development and the decline in lycopene as well as in the other carotenoids were seen in the bitter gourd aril held at this temperature.
It was proposed that carotenoids in the pericarp and aril of bitter gourd fruits are synthesized by two alternative pathways in which β-carotene is not formed from the lycopene.