| Broccoli inflorescence is a good source of health promoting compounds since it contains carotenoids, vitamin C, tocopherols (vitamin E), glucosinolates, polyphenolics and other minor compounds. Recent studies have shown the relevant bioactive components against various types of cancer and cardiovascular diseases. This paper studied the effects of different nitrogen supply on quality and antioxidant activity in heads of broccoli, the objectives are to know how nitrogen affect the nutritional quality and antioxidant activity in heads of broccoli. The results are summarized as follows:The effects of (5, 10, 15 and 20 mmol·L-1) on the head growth, nutrition quality were investigated in two broccoli (Brassica olerecea var. italica) cultivars (late maturity cv. Malasong and middle early maturity cv. Lüyou No.2 ) by inorganic medium culture.The results showed that plant height, head diameter, head fresh and dry weight increased with increasing nitrogen supply, simultaneously also improved soluble protein, free amino acid and nitrate accumulation, but the Mg content, the Vc, the soluble total sugar decreased, these suggeated that the suitable level is advantageous to enhances the broccoli nutrition quality and the antioxidant ability.The results showed that the content of chlorophyll, carotenoid, net photosynthetic rate (Pn) and stomatal conductance (Gs) increased significantly with increasing the supply of nitrogen nutrition, but intercellular CO2 concentration (Ci) decreased. Nitrogen application was little affected on chlorophyll fluorescence characteristics in leaves of broccoli, however, in comparison with the lower nitrogen supply, the actual efficiency of PSII (ΦpsII), photochmical quenching (qP), maximal photochemical efficient (Fv/Fm) was promoted in higher nitrogen supply, at the same time non-photochemical quenching (qN) was inhibited. These results suggested that increased nitrogen applied was benefical to promote photosynthetic capacity in broccoli to a certain extent.The results showed that total phenolic content decreased with increasing nitrogen supply in heads of broccoli, especially when applied nitrogen level was higher than 10 mmol·L-1. Quercetin and kaempferol were identified in broccoli head, and kaempferol content was 1.48 times higher than quercetin content, and their contents reached highest level when applied nitrogen concentration was 5 mmol·L-1. Increasing nitrogen supply decreased DPPH radical scaveging and FRAP value, and markedly inhibited the antioxidant activity in broccoli head when nitrogen supply level was 20 mmol·L-1 . A significantly positive correlation was found between FRAP value and the phenolic content in two cultivars. Compared with two cultivars, the head growth of cv. Malasong was better than that of cv. Lüyou No.2, but was contrary to total phenolic and antioxidant activity. These results clearly demonstrated the phenolic substances and antioxidant activity in broccoli were strongly affected by fertilizer regimes especially nitrogen application level. The antioxidant matters availably advanced with increasing nitrogen supply. The content ofβ-carotene and lutein were the highest on the higher nitrogen level 15mmol·L-1.the antioxidant matters were positively correlated with the total N content of head in broccoli at significant level. These suggested that the higher nitrogen level 15 mmol·L-1 is advantageous to enhance the broccoli nutrition quality and the antioxidant matter.The effects of nitrogen deficiency (0 mmol·L-1) and excessive nitrogen supply (40 mmol·L-1) on the flavonoids, PAL and PPO activity were investigated in two broccoli cultivars leaves (early maturity cv. Qingfeng and middle maturity cv. Liiyou No.2 ) by inorganic medium culture. The results showed that flavonoid content on deficiency treatment was signific4ntly higher than excessice nitrogen treatment and control (15 mmol·L-1), Increasing nitrogen supply level significantly decreased the activity of PAL and PPO. |
