Comparative study on functional components, antioxidant activity and color parameters of selected colored leafy vegetables as affected by photoperiods

Five selected leafy vegetables with different leaf color were evaluated for their functional components, antioxidant activity and color parameters grown under different levels of photoperiod. All vegetable plants were grown in controlled chamber under the levels of photoperiod as 6, 12, 18 and 24 hours. The leaves of vegetables plant contained the highest content of betacyanin, chlorophyll, total polyphenol and antioxidant activity under a 12 hour and the lowest was found in a 24 hour photoperiod. The highest contents at every photoperiodic level were in the order of red amaranth>red beet>swiss chard>red spinach>green amaranth for betacyanin; red amaranth>red spinach>swiss chard>red beet>green amaranth for chlorophyll; red beet>swiss chard>red spinach>red amaranth>green amaranth for total polyphenol. The highest antioxidant activity was found in red amaranth as followed by red beet, red spinach and swiss chard under a 12 hour photoperiod, while green amaranth had the lowest activity at every photoperiodic levels. Strong positive correlations among functional components and antioxidant activity suggest that combined functions of both enhanced the best antioxidant activity under a 12 hour photoperiod. The deeper color (higher redness value and lower yellowness value) with lower lightness value in red-fleshed leafy vegetables and the brighter color (lower redness value and higher yellowness value) with higher lightness value in green amaranth were observed under different photoperiodic levels. Compared to the other studied vegetable species, red amaranth was more sensitive to the variation in betacyanin than in chlorophyll content.