Claire Kevers

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 assessing 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 polyphenol contents (TPCs) and individual phenolic compound contents of all the juices were investigated. 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 assay, 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 compounds contained in fruit and vegetable juices, the PMA–whole blood assay appears better than the ORAC assay for evaluating juice antioxidant capacity.

The real impact of polyphenol-rich vegetable and fruit juice intake on cardiovascular health remains a matter of controversy. In the present study, rat aorta segments immersed in an organ bath (OB) were used to explore whether the total polyphenol content and/or individual phenolic compound contents of 22 commercial vegetable (n = 3) and fruit juices [(citrus (n = 5), berries (n = 10), apple (n = 2), pineapple (n = 2)] might be associated with vascular tone. Red juices (particularly blackcurrant) and lemon juice caused the most marked vasorelaxation, its amplitude being endothelium dependent or not according to the volume ratio of juice to initial OB solution V_juice/V_OBS). At volume ratios 5% and 10%, both the juice and OB total polyphenol for all juices and total anthocyanin contents for berry juices significantly correlated with aorta vasorelaxation intensity. This was not the case for total or individual flavonols (except kaempferol) or for total or individual flavanols (except epigallocatechin gallate). If one relates our measured concentrations of individual phenolic compounds in OB to what is known about their physiological concentrations, and given our evidenced correlations between compound concentrations and vasorelaxation intensity, kaempferol, epigallocatechin gallate and peonidin-3-O-glucoside seem to emerge as the interesting phenolic compounds likely to be responsible for the potent vasorelaxation observed with fruit juices, and more particularly blackcurrant ones. Clinical investigation is required, however, to confirm our observations.

Polyphenol compounds present in high quantity in wines are well-known to have potent cardio-protective properties through several biological mechanisms including antioxidant activity. A large number of methods have been developed for evaluating the antioxidant capacity of food matrices. Most of them have, however, the disadvantage of being time consuming and require specific analytical protocols and devices. In the present study, we present the electrochemical PAOT (Pouvoir Antioxydant Total)-Liquid^® Technology which can be easily used by winemakers for evaluating antioxidant activity of wine during all steps of making process. The methodology is based on the measurement of electric potential variation resulting from chemical reactions between wine polyphenols and a free radical mediator M^• as source of oxidants. Total antioxidant activity as estimated by the PAOT-Liquid^® activity was 6.8 fold higher in red wines (n = 14) when compared to rosé (n = 3) and white (n = 3) wines bought in a commercial market. Moreover, PAOT-Liquid^® activity was highly correlated with total polyphenols content (TPC) of all wines (r = 0.9540, p < 0.0001) and the classical DPPH (2,2-diphenyl-1-picryhydrazyl) assay which is often used for evaluating antioxidant capacity of food matrices (r = 0.9102, p < 0.0001).

Yams (Dioscorea spp.) are tuber crops used as staple food in Africa because of their nutritional value. In contrast to the inefficiency of traditional method of planting, micropropagation by nodal cuttings allows to increase the multiplication and the rapid production of pathogen-free plant material. In this work, micropropagation of yam from both nodal cuttings and microtubers was first tested and compared. It appears that microtubers rapidly develop shoots, more rapidly than nodal cuttings. Respectively 16 and 28 weeks are needed to obtain 10 cm high shoots. In a second time, the two techniques of multiplication were used in parallel to improve the multiplication rate. So, one nodal cutting after 28 weeks of culture can be subcultured as nodal cuttings (for 28 other weeks) and as microtuber parts (for 16 weeks). At the end of each subculture of nodes or microtubers, nodal cuttings and microtubers were cut and subcultured. This technique allowed obtaining more rapidly a lot of microtubers. The use of nodal cuttings allowed obtaining about 3×10⁴ cuttings in two years. The additional use of the formed microtubers and the division of the microtubers at the subculture in three parts increased this multiplication rate by 15. The importance of this work was to consider microtubers not only as final planting product, but also to include them in the in vitro multiplication protocol to drastically increase the production of cuttings and finally of microtubers.