Hello,
This week I measured the DPPH scavenging activity (%) and the antioxidant activity expressed in VCAE in 2 varieties (red and yellow) of onions. (Find protocol attached).
Unfortunately the DPPH scavenging activity of the extracts shows very high levels. I'm not sure if I'm right with the procedure and if I maybe have to first dilute my extracts before I measure them?
my results are also attached.
Free-radical scavenging capacity and antioxidant properties of some selected onions (Allium cepaL.) and garlic (Allium sativum L.) extracts
ABSTRACT
The radical scavenging activity (RAS), chain-breaking activity, H2O2-scavenging, reducing capacity and total phenolics of four types of onions (Green onion, Yellow, Red and Purple) and garlic were investigated. Total phenolics varied from 30 mg (green onion) to 49 mg.100 g-1 fresh weight (garlic). Garlic extract showed the highest RAS, while green onion showed the lowest one. The chain-breaking activity of green onion extract was higher (0.48) than garlic extract (0.029). Chain-breaking activity of yellow, red and purple onion extracts was 0.19, 0.048 and 0.032 respectively. However, heating treatment (90 ºC, 3h) caused an increase in this activity. Low ability of green onion extract to scavenge hydrogen peroxide was noted (35%), whereas high ability was noted in other onion and garlic extracts and ranged from 60 to 90%. The lowest reducing capacity was noted in green onion extract (18%), whereas the highest in garlic extract (196%). Statistically, high significant correlations were observed between total phenolics content and reducing power, scavenging of hydrogen peroxide and chain-breaking activity of extracts.
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-89132005000600011
I want to suggest you re-dilute your extract before you react it with DPPH
Dear Maria,
I think you have done the assay perfectly well. indeed the results are very encouraging and your concentretions are correct and need no further dilutions.
Regards.
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