Antioxidant capacity and total phenolics of Cyphostemma digitatum before and after processing: use of different assays

In the framework of standardisation of new healthy food sources, this paper aimed to study the total phenolics and the antioxidant power of Cyphostemma digitatum (Vitaceae) in water and ethanol extracts, using 96-well micro plates with BMG FLUOstar Optima micro plate reader. Total phenolics by Folin-Ciocalteu method in the water extracts were significantly lower after processing, decreasing from 1.41 +/- A 0.06 g GAE/100 g in the raw leaves to 0.80 +/- A 0.08 g GAE/100 g in the processed sample; the ethanol extract revealed the same trend with higher values, decreasing from 1.95 +/- A 0.03 to 1.56 +/- A 0.12 g GAE/100 g. The antioxidant capacity was elucidated by four methods: TEAC, DPPH, FRAP and ORAC. No or very weak correlations were found between antioxidant assays and total phenolics; this confirms that the antioxidant capacity could be attributed to other molecules. The ORAC assay proved to be more powerful than the other assays; it showed 103.3 +/- A 2.5 mmol/100 g Trolox equivalents in the raw leaves ethanol extract and 91.9 +/- A 3.0 mmol/100 g in the processed sample. ORAC assay showed the opposite for the water extract where the antioxidant capacity increased from 16.7 +/- A 0.2 to 41.7 +/- A 2.7 mmol/100 g Trolox equivalents after processing, which could be attributed to new water-soluble compounds generated in the consumed form.