To determine total vitamin C we adapted the protocol described in [37].Thus,a 200L aliquot of the above-mentioned filtrate was incubated for 15 min at room temperature with 100L 200mM DTT in 400 mM Tris base which generated a final pH of 6–6.8.Then,the reaction was stopped by acidification with 100L of 8.5% ortophosphoric acid.