Ex Vivo Antioxidant Capacities of Fruit and Vegetable Juices. Potential In Vivo Extrapolation

Background: In support of claims that their products have antioxidant properties, the food
industry and dietary supplement manufacturers rely solely on the in vitro determination of the
ORAC (oxygen radical antioxidant capacity) value, despite its acknowledged lack of any in vivo
relevance. It thus appears necessary to use tests exploiting biological materials (blood, white blood
cells) capable of producing physiological free radicals, in order to evaluate more adequately the
antioxidant capacities of foods such as fruit and vegetable juices. Materials: Two approaches to as sessing the antioxidant capacities of 21 commercial fruit and vegetable juices were compared: the
ORAC assay and the “PMA–whole blood assay,” which uses whole blood stimulated by phorbol
myristate acetate to produce the superoxide anion. We described in another paper the total poly phenol contents (TPCs) and individual phenolic compound contents of all the juices investigated
here (Matute et al. Antioxidants 2020, 9, 1–18). Results: Ranking of the juices from highest to lowest
antioxidant capacity differed considerably according to the test used, so there was no correlation (r
= 0.33, p = 0.13) between the two assays when considering all juices. Although the results of the
ORAC assay correlated positively with TPC (r = 0.50, p = 0.02), a much stronger correlation (r = 0.70,
p = 0.004) emerged between TPC and % superoxide anion inhibition. In the PMA–whole blood as say, peonidin-3-O-glucoside, epigallocatechin gallate, catechin, and quercetin present in juices were
found to inhibit superoxide anion production at concentrations below 1 µM, with a strong positive
correlation. Conclusions: Associated with the determination of total and individual phenolic com pounds contained in fruit and vegetable juices, the PMA–whole blood assay appears better than the
ORAC assay for evaluating juice antioxidant capacity