I have not performed the FRAP test, but in the principle of the FRAP assay,  tissue homegenates are available to the test. The most important things are that your sample can be dissolved in the reaction solution and your samples have proper activities, otherwise the data will show no activities. In my opinion, ORAC assay is the most sensitive assay to measure anti-ox activity using tissue homogenates or serums. I recommend you to perform FRAP and ORAC, because you may not get good data from FRAP.

yes u can do FRAP assay on both animal tissue and plant extract.

FRAP is used to assess total antioxidant capacity in either human serum or plant extract by measuring free ferric ions quantitatively through color formation. So you can use it

you can use FRAP assay to evaluate the antioxidant capacities in both serum or plant extract. in the beginning frap assay was used just in the serum and adapted after in plant extract.

you can evaluate the antioxidant enzymes in the liver homogenates like catalase, superoxide dismutase, malonedialdehyde, ...