I am doing antioxidant tests on kefir and using supernatant for the tests. But I’m getting confused about the way to find TPC value as I'm not sure whether the concentration of supernatant is the same as concentration of sample.

The procedure is like this:

I took 10 g (10.2 ml) of sample (kefir), added with 100 ml ethanol (95%) and Hcl (1N) (v/v, 85/15) for extraction. After shaking for 1 hour, the solution is centrifuged and the supernatant is used to test for TPC. The weight of supernatant I get is 66.44g (67.5 ml). Then I took 1 ml of supernatant and mixed it with 0.5 ml of 1N Folin Ciocalteu Reagent and 6ml of distilled water for 5 minutes and later 1 ml of 5% Na₂CO₃ is added. After incubation for 30 minutes, the absorbance was measured at 725 nm against ethanol and Hcl blank.

The equation I get is y=3.74x + 0.0017, R² = 0.9889, absorbance at 725 nm is 0.035

How to find the TPC value in mg GAE/100g sample and mg GAE/100ml of sample? Is the concentration of supernatant same as sample? Please advise me. Thank you.