排序方式： 共有3条查询结果，搜索用时 9 毫秒
1
1.
Dried ground leaves ofPsidium guajava L. (guava) were extracted by water and aqueous ethyl alcohol 50% (1∶10) ratio, and the total phenolic content in the extracts
was determined spectrophotometrically according to Folin-Ciocalteu's phenol method and calculated as gallic acid equivalent
(GAE). Remarkably high total phenolic content 575.3±15.5 and 511.6±6.2 mg of GAE/g of dried weight material (for ethanol guava
leaf extracts and water guava leaf extracts, respectively) were obtained. The antioxidant activity of lyophilized extracts
was determined at ambient temperature by means of a 2,2-diphenyl-1-picrylhydryzyl (DPPH') colorimetry with detection scheme
at 515 nm. The activity was evaluated by the decrease in absorbance as the result of DPPH' color change from purple to yellow.
The higher the sample concentration used, the stronger was the free radical-scavenging effect. The results obtained showed
that ascorbic acid was a substantially more powerful antioxidant than the extracts from guava leaf. On the other hand, the
commercial guava leaf extracts and ethanol guava leaf extracts showed almost the same antioxidant power whereas water guava
leaf extracts showed lower antioxidant activity. The parameter EC50 and the time needed to reach the steady state to EC50 concentration (T
EC
50) affected the antiradical capacity of the sample. The antioxidant efficiency (AE) has been shown to be a more adequate parameter
for selecting antioxidants than the widely used EC50. This study revealed that guava leaf extracts comprise effective potential source of natural antioxidants. 相似文献
2.
He?Bing?Email author Yang?Xiao-e Ni?Wu-zhong Wei?You-zhang Ye?Hai-bo 《浙江大学学报(A卷英文版)》2003,4(4):474-479
Lead concentrations in roots, stems and leaves of accumulating and non-accumulating ecotypes ofSedum alfredii (Hance) were studied through a hydroponic experiment with different Pb concentrations supplied as Pb(NO3)2. Lead concentrations in leaves and stems of the accumulating ecotype were 4–9 times and 3–5 times those of the non-accumulating
ecotype, and Pb-accumulated amounts in stems and leaves of the accumulating ecotype were 4–9 times and 8–11 times higher than
those of the non-accumulating ecotype, respectively. The results indicated that the accumulating ecotype had better ability
to transport Pb from roots to shoots. The subcellular distributions of Pb in the root, stem and leaf tissues were studied
using sucrose differential centrifugation. Approximately 50% of Pb contents was found to be associated with the cell wall
fraction in stems of the accumulating ecotype and the percentage increased to 80% both in roots and leaves, no matter when
plants were grown with different levels of Pb. The results indicated that the distribution of Pb on cell walls of the accumulating
ecotype could mainly account for the high tolerance to Pb.
Project supported by a Key Project from the Educational Ministry of China (No:02180) and by the Outstanding Young Scientist
Grant from the National Natural Science Foundation of China (No: 39925024). 相似文献
3.
1