Effect of the Media in the Folin-Ciocalteu Assay for the Analysis of the Total Phenolic Content of Olive Products

The nutritional and economic value of oils is affected by its antioxidant properties linked to their total phenolic content (TPC). The analysis of antioxidants such as phenols may be affected by the lipophilic character of the media. Therefore, the accurate determination of TPC in oils deserves particular attention. This research has tested the effect of the alkaline medium in the quantification of TPC in extra virgin olive oil (EVOO) and olive pomace oil (OPO) using the Folin-Ciocalteu method. Seven different EVOO and OPO oils were used to gain representativity and study matrix effects in the analysis. Among the alkaline conditions assayed, the Folin-Ciocalteu method led to maximum TPC in EVOOs samples using 7.5% Na2CO3, whereas 35% Na2CO3 showed better characterization of TPC in OPOs than milder basic conditions. Therefore, when analyzing olive oil products, adjusting the alkaline media in the Folin Ciocalteu assay is important for optimal TPC determination. TPC analyses via Folin-Ciocalteu with different media was supported with antioxidant activities determined with reference assays: 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid cation radical and 2,2-diphenyl-1-picrylhydrazyl radical.