| Epidemiological studies indicate a significantly negative correlation between the consumption of vegetables and incidence of cancer and cardiovascular diseases. The protective effect of vegetable has been attributed to the their antioxidant constituents,including ascorbic acid, α -tocopherol, β -carotene and phenolic compounds. It has been reported that the antioxidative ability of phenolic compounds is more greater than those of ascorbic acid and α -tocopherol. The antioxidant potential of vegetables is influnced by genetic, and environmental factors, postharvest and processing. The effects of genotype, seasons, locations, selenium addition and pickling on the contents of antioxidant compounds and antioxidant potential in Chinese Brassica vegetables were studied in this paper and the interactions of genotype and environment were analysed. The results are summarized as follows:1 Effect of different seasons on the contents of ascorbic acid, glutathione, carotenoids in different genotypes of leaf mustard, pakchoi, caixin and purple caitai.The results showed that the contents of ascorbic acid, glutathione, lutein and β-carotene were significantly influenced by genotypes and seasons. Leaf mustard planted in late autumn and harvested in spring had significantly higher contents of ascorbic acid, glutathione, lutein and β -carotene than those planted in early autumn and harvested in winter (P<0.01). Pakchoi planted in early autumn harvested in late autumn had significanly higher levels of ascorbic acid, glutathione, lutein and β -carotene than those planted in spring harvested in summer (P<0.01). The differences of ascorbic acid, glutathione, lutein and β-carotene between caixin and purple caitai were significant (P<0.01). There were significantly positive correlations between lutein, β -carotene and chlorophyll contents, and between ascorbic acid and glutathione.2 Effects of different seasons on the contents and composition of phenolic compounds, and antioxidant potential in different genotypes of leaf mustard ,pakchoi, caixin and purple caitaiLeaf mustard planted in late autumn and harvested in spring had significantly higher levels of total phenolics and antioxidant potential than those planted in early autumn and harvested in winter. Pakchoi planted in early autumn and harvested in late autumn had significantly higher levels of total phenolics and antioxidant potential than those planted in spring and harvested in summer. Quercetin and kaempferol were the main fiavonols in leaf mustard, pakchoi and caixin and purple caitai. The kaempferol contentwas considerably higher than quercetin content. Both quercetin and kaempferol content were influenced by seasons. Leaf mustard harvested in spring had much higher levels of quercetin and kaempferol contents than those harvested in winter. Pakchoi harvested in autumn had much higher levels of quercetin and kaempferol contents than those harvested in summer.The effects of genotypes, seasons and the interaction of genotype x season on the phenolic contents and antioxidant potential were significant. The antioxidant potential with different assays were significantly correlated with the total phenolics content (P<0.0l) and favonols (.PO.05), respectively. The results indicated that antioxidant potential could be increased by selecting variety having higher phenolics content, or planting plants in a suitable season.3 Effects of different locations on the contents of phenolic compounds and antioxidative potential in different genotypes of leaf mustardTen genotypes of leaf mustard were grown at four locations including Xinchang, Hangzhou, Jiaxing, Wenzhou. The results showed that leaf mustard from different locations had significant differences in the phenolic compound contents and antioxidant potential.The leaf mustard from Wenzhou was the highest in the phenolic compound contents and the antioxidant potential, followed by the leaf mustard from Jiaxing, Xinchang, and Hangzhou. The relationships between phenolic compound contents and antioxidant potential and climatic and soil factors were analyzed. The average grey relevance coefficient of climatic factors ranged from 0.2652 to 0.5919, the average grey relevance coefficient of soil factors ranged from 0.2054 to 0.7630. The influence of average soil surface temperature was the greatest among climatic conditions.The influence of organic matter was the biggest among soil conditions. There were significant differences of genotypes, locations and the interaction of genotype x location (P<0.01).The results indicated that the phenolic compound contents and antioxidant potential was not only influenced by genotypes, but also affected by environment conditions. A significantly positive correlations were found between the contents of total phenolics, flavonoids and phenolic acids and antioxidative potential with three assays (DPPH inhibition, TEAC value and FRAP value). The phenolic compounds were the major contributor to the antioxidant Potential.4 Effects of four levels of selenate (0, 1, 5 and 20 umol/L) on nutritional quality, phenolic compounds and antioxidant potential in two genotypes of pakchoiThe results showed that plant growth was promoted by low concentration of selenate in the nutrient solution (1 umol/L), however inhibited by high concentration of selenate(20nmol/L). With the increase of selenate concentration, total soluble sugar and soluble protein was first increased and then decreased, and total free amino acids were reverse. However, there were no significant differences among treatments (/>>0.05). There was a significantly positive correlation between selenium content in the plant and selenite concentration in the nutrient solution. With the increase of selenite concentration in the nutrient solution, the contents of ascorbic acid and gluthathione were increased and reached to the highest at 5 jxmol/L level, GSH-Px activity was increased and the highest at 20 \imo\fL level, however, the total phenolic content was decreased. Compared with the control, the contents of quercetin, kaempferol and phenolic acid were decreased. The antioxidative potential (DPPH inhibition and TEAC value) were first increased and later decreased.5 Effects of different form of selenium (Selenite and selenate ) on the growth, quality and antioxidant potential in pakchoi (Brassica campestris ssp.chinensis L.)The results showed that the plant growth was promoted at 5.0 p mol/L Na2SeC>3 and 1.0 u mol/L Na2SeC>4. Significant differences in the contents of selenium in different parts of Pakchoi were found between selenite and selenate treatments. The contents of selenium in both leaves and root had significantly positive correlation with the selenium concentration in the solution (PO.01). With the increase of selenium concentration, the contents of soluble sugar and reducing sugar in leaves were increased, while the content of sucrose was decreased, the content of cellulose was increased at first, then decreased in selenite and selenate treatments. The protein content were increased with increasing selenium concentration, while total free amino acid content were decreased. The contents of ascorbic acid and reduced glutathione (GSH) in leaves by treated with selenate were along increased with increasing selenium concentration, that in shoot by selenite treated was increased at low concentration, then decreased at high concentration.A significantly positive correlation was found between selenium concentration and the GSH-Px activity, and a more efficient increase in GSH-Px activity was obtained with selenate-enriched leaves than with selenite-enriched leaves. No significant differences were found between the selenium treatment and control (P>0.05). The effects of selenite and selenate on the antioxidant potential were determined using DPPH and TEAC methods. The DPPH radical scavenging activity and total antioxidant activity (TEAC) were enhanced at 5.0 u mol/L Na2SeO3 and 1.0 ymol/L Na2SeO4, and inhibited at 5.0 u mol/L Na2SeO4.6 Effects of pickling on nutritional quality of pickled leaf mustard (cv. Xuelihong and cv.Liuzijiecai)Nitrate contents in leaf mustard during pickling were decreased. The nitrate content in cv. Xuelihong and cv. Liuzijiecai decreased quickly within 7 days and 14 days of pickling, respectively, The nitrate content in cv. Xuelihong was lower than that in cv. Liuzijiecai (P<0.05). The nitrite content in leaf mustard during pickling was increased first and decreased later. The nitrite content in cv. Xuelihong and cv. Liuzijiecai increased quickly from 7 to 21 days and 14 days during pickling,respectively. The nitrate content in cv. Xuelihong was lower than that in cv.Liuzijiecai (P>0.05).Total soluble sugar, reducing sugar, sucrose content and total soluble protein of pickled leaf mustard were gradually decreased during pickling, but total free amino acid content showed a gradually increased trend. There was a significant difference between cv. Xuelihong and cv. Liuzijiecai.7 The effects of pickling on the contents of antioxidant compounds and antioxidant potential in different genotypes of leaf mustardThe contents of ascorbic acid, total phenolics, total flavonoids and antioxidant capacity (TEAC assay and FRAP assay) were determined in fresh and pickled leaf mustard. Compared with fresh leaf mustard, the contents of antioxidant compounds and antioxidant potential decreased in pickled leaf mustard. However, the content of quercetin and kaempferol were increased. The genotypic differences of antioxidant potential were significant between four genotypes of leaf mustard. After pickling, the decreases in antioxidant potential of cv. Sunke Qingcai and Liuzi Jiecai were higher than those of cv. Jinsijie and Xuelihong. There were significantly positive relationships between the total phenolics, the total flavonoids and antioxidant potential. However, the relationship between the ascorbic acid content and antioxidant potential was not significant.In the picked leaf mustard, flavonoids were the major contributor to the antioxidant Potential.
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