First question that comes to mind when reading Your post is - how do You define high and low antioxidant activity (in comparison to what is it high, how do You express it) - because there are many lapses in that even in published papers. If something shows high FRAP it usually should show high chelating activity. It is also impossible to have high total flavonoids and low chelating activity since they are analyzed by their ability to create colored chelat complexes with aluminium cations. In general You should find the feature about plant extract that is most important for Your product. In fish products most important issues might be oxidation of fat or oxidation caused by metals from cans. Than You should pick one assay that will measure activity mostly related with the changes You are trying to prevent. Beta-carotene/Linoleic acid assay is good to present ability to prevent oxidation of unsaturated fats, therefore it should be really good for Your purpose. I suggest to optimize concentration (based on the analysis) to the level at which it prevents oxidative changes in as much unsaturated fat as fish product You want to preserve contains.

Here are some papers that might be useful:

Koleva, I. I., van Beek, T. A., Linssen, J. P. H., Groot, A. d. and Evstatieva, L. N. (2002), Screening of Plant Extracts for Antioxidant Activity: a Comparative Study on Three Testing Methods. Phytochem. Anal., 13: 8–17. doi: 10.1002/pca.611

Y. S. Velioglu , G. Mazza , L. Gao , and B. D. Oomah. Antioxidant Activity and Total Phenolics in Selected Fruits, Vegetables, and Grain Products J. Agric. Food Chem., 1998, 46 (10), pp 4113–4117 DOI: 10.1021/jf9801973

Thanks for helping me and your kind suggestion.

Is there any probable reason for decrease in DPPH radical scavenging activity and FRP with the increase in concentration? I found in ginger extracts.

What Krystyna said is absolutely right. You should screen assays that best meet your desired matrix. In the case of fish, the oxidation of fat might be the most desired reaction to halt, and therefore, like she said, B-carotene/linoleate would be interesting to do, even TBARS would be interesting for its sensibility. If you need I can point you some interesting papers.

Hope this helps!

after heart greetings to all of you

i did also DPPH assay and total phenols by Folin–Ciocalteu reagent for air dried tomato,grape and potato peels (air forced oven 50 °c / 24 hr ) ethanolic extract ( ethanol 50%) .

the main problem i faced is : how to optimize the amount of dried peels which extracted for total phenols assay , total phenols concentrate is high in grape peels then tomato and low in potato ( while ethanolic extraction, large amounts up to 50mg the color is so dark , and with smaller amounts the color is so pale for potato and tomato ) and i want to compare between their total phenolic content

Ahmed M. Abdo the best way to compare total phenolic content in Your case would be to calculate their concentration per 100 g of dry weight of analyzed material (peels).

Knowing how much peels (in g) peels was used to prepare the extract and based on F-C assay what is the concentration of phenolics in extract You can express phenolics per 100 g of peels dry weight (You have to also consider how much moisture is in the peels You used for the extracts).

In that case You can use different concentrations of peels in the extract which is probably necessary to use spectophotometric assay as the Absorbance of analyzed samples should not exceed 1.0 (according to Lambert - Beer linear law).

I hope this helps.

You can add different concentrations of extracts in fish products, evaluate the quality of products after prolong storage periodically and finally get sensory evaluation

Thanks! Sir

Krystyna Pogoń

thank you

with all my respect and appreciation

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