Hi Nabila,

The determination of antioxidant activity or radical scavenging activity is depending on the procedure assay.

Please, see the following articles

Article On-Line Screening, Isolation and Identification of Antioxida...

Article Applicability of an improved Trolox equivalent antioxidant c...

Article Applicability of an improved Trolox equivalent antioxidant c...

Article Antioxidant capacity of reaction products limits the applica...

Yasmine Chemam , Bensouici Chawki , I think that you can help her

Thank you.i will try to read and understand first. I confused how i want to relate the trolox stndard/trolox equivalent with RSC% at which RSC%=( Abs blank-Abs sample/Abs blank)×100. Why i need to used the trolox then? Imad Mennai

Trolox equivalent/g dry weight can be calculated by creating a standard curve of  Trolox standards versus their absorbance. From here substitute the absorbance you got for your seaweed sample into equation of the line. eg lets say you got an absorbance of 0.265 for your seaweed sample and lets say your equation of a line is y = -0.0006x + 0.6988, then =((0.265-0.6988)/-0.0006) which gives 723.00 trolox Equivalents (µM), depending on the concentration of Trolox you used in your standard curve.

Indeed, The papers below explain how to calculate antioxidant activity in uM (or mg) TE/g of sample: Article High-throughput micro plate assays for screening flavonoid c...

Article Influence of extraction conditions on ultrasound-assisted re...