The total polyphenol content and antioxidant activity were compared in the leaves of seven red amaranth (Amaranthus tricolor L.) cultivars. The effect of the sunlight level on the accumulation of total polyphenol content and antioxidant activity was also investigated by growing plants under full sunlight and shaded conditions. The total phenolic content and antioxidant activity differed among the cultivars studied, and leaves from the cultivar 'Rocto Joba' and 'Rocto Lal' had the highest phenolics and antioxidant activity, respectively. These values were lowest in the leaves of the cultivar 'Red Queen'. Comparatively, red-fleshed cultivars had more total polyphenols and antioxidant activity than red green-fleshed cultivars. Total polyphenol and antioxidant activity were greater in leaves from plants grown under full sunlight without shading. The positive correlation between antioxidant activity and total polyphenols (R 2 = 0.824) suggests that phenolic compounds are the major antioxidant components in red amaranth. The results indicate that red amaranth containing high phenolics may provide a source of dietary antioxidants. The combination of cultivar variation and responsiveness to specific growing conditions can create opportunities for the production and processing of vegetable red amaranth with improved antioxidant properties.

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Foliar Application of Salicylic Acid Improved the Growth, Yield and Leaf's Bioactive Compounds in Red Amaranth (Amaranthus tricolorL.)This study was conducted to determine the effect of foliar salicylic acid (SA) applications on growth, yield and bioactive compounds of red amaranth grown under greenhouse conditions in 2008 at Gifu University, Japan. SA was applied at three different concentrations (10-3, 10-4and 10-5M), three times during the vegetation at 7-day intervals one week after sowing. Growth parameters (plant height, stem length, number and size of leaves, root length) and yield (fresh and dry matter weight) were recorded from treated and control plants on 28 days after sowing. Among bioactive compounds, betacyanins, chlorophyll, total polyphenol and antioxidant activity were the determined from the leaves of treated and control plants. All of three doses SA application enhanced the plant growth, yield and leaf's bioactive compounds compared to the control. The growth parameters and yield of red amaranth was significantly influenced by foliar SA applications. The highest yield, antioxidant activity, amount of betacyanins, chlorophyll and total polyphenol occurred in 10-5M SA treatment. According to our results, applications SA at rate of 10-5M should be recommended in order to improve yield and bioactive compounds in red amaranth.

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Seven cultivars of red amaranth (Amaranthus tricolor L.) with different leaf color were evaluated for their betacyanin and chlorophyll content at two stages of development. The effects of food processing factors such as thermal treatment, light, H2O 2, and prolonged storage on betacyanin extracts were also examined. Betacyanin concentrations were highly correlated with the leaf color index and the cultivars (Rocto joba, BARI-1, and Altopati) with better color index tended to be associated with high betacyanin. Within a shoot canopy, the apical leaves accumulated higher betacyanin than those of middle and basal leaves. While the highest concentrations of chlorophyll were found in BARI-1, however Red queen had the lowest concentrations. Color index of leaves and betacyanin concentrations were increased and chlorophyll concentrations were decreased with the plant age, which indicate that change of these colorant pigment concentrations with plant age enhance the red leaf formation in red amaranth. Low temperature, darkness, and free or low oxidants maintained the stability of betacyanin concentrations of red amaranth; prolonged storage degraded the betacyanin. Variable factors such as the cultivar of red amaranth, its degree of maturity, and the food processing factors have been shown to have a quantitatively important influence on betacyanin yields and preservation.