Which biomarkers are you referring to specifically? I know that cells can be frozen at -80°C and then removed later to determine enzymatic activity in relation to oxidative stress (ie, catalase activity). 

For instance antioxidants as vitamines and enzymes, ROS, etc

I wonder if the time that they spent at -80ºC or -40ºC has an effect in their concentration on blood and plasma.

Regards!

If you store your samples correctly, be it -80°C or -40°C, then you should have no problems.

Cheers!

Would you be so kind to recommend me a paper showing it?

Mostly interested in dROMs, FRAP assay, carotenoids, vit E, TBARS and antioxidant enzymes

Thanks for the answer, Hugo!

Even it the samples are frozen at -80ºC?

Have you tried to include storage time as variable in one of your experiments? or do you know a publication which tested it?

Best regards,

Dear Chibuike C Udenigwe:

Many thanks for your carifying answer! I will read the publications inmediatly!

I plan to keep the samples during 4 months in a freezer et -80C if possible, before sending them (at -20, probably -40, during 3 days).

What do you think?

Best regards,

Dear Chibuike C Udenigwe:

Many thanks for your answer!

Could you be so kind to give me an example of conditions that can lead to further oxidation?

Best regards,