Reactive oxygen species (ROS) are vital for the functioning of the cellular system. However,
the excess production of ROS, whether due to endogenous or exogenous factors, can cause damage to biomolecules, possibly leading to the development of cardiovascular or
neurodegenerative diseases, or even cancers. The NADPH oxidase enzyme complex (NOX
complex) plays an important role in the production of ROS in leukocytes, specifically in
neutrophils. The formation of oxidants such as superoxide anion and hydrogen peroxide are attributed to NOX complex with the participation of myeloperoxidase (MPO). These oxidants serve as the basis for the formation of other oxidants such as hypochlorous acid and hypothiocyanous acid, causing inflammatory responses. However, moderate production of ROS allows the expression and activation of the Keap1/Nrf2/ARE pathway leading to the expression of certain antioxidant enzymes. On the other hand, to counteract the excess of ROS there are both enzymatic and non-enzymatic antioxidants, in the latter group, the great family of polyphenols with antioxidant properties stands out. Polyphenols, which have antioxidant properties, are compounds present in fruits, vegetables, beverages and are commonly consumed in diets. Around the world there
are varied diets that contain products rich in polyphenols. The Mediterranean diet composed of a wide range of fruits and vegetables, cereals, bread, pasta, fiber and phytochemicals has been the subject of several studies to date. It has been shown that the Mediterranean diet correlates with the low incidence of several chronic diseases, attributing these effects to products rich in polyphenols. For instance, consuming products rich in polyphenols correlates up to 36% with a reduction in the risk of hypertension.
In this research thesis, we quantified the total polyphenols content (TPC) as well as some
polyphenol subclasses (flavan-3-ol, flavonols and anthocyanins) by Ultra-Performance Liquid Chromatography (UPLC), present in several fruit and vegetable juices available on the French, Belgian and German markets. In the same way, we evaluated the antioxidant capacity of these juices using the in vitro ORAC (oxygen radical antioxidant capacity) method, which is a method mostly used by the industry to determine the antioxidant capacity of products. However, this method is not really standardized, nor does it have physiological relevance. Under in vivo conditions, increased superoxide anion free radical production results from mitochondrial respiratory chain and endothelial dysfunctions, xanthine oxidase activation, and activation of cellular NADPH complex in neutrophils. The inhibition of superoxide anion production was tested according to the protocol described by Baptista et al. (2012) on PMA activated whole blood (Chemiluminescence Method).
To evaluate the vascular reactivity, rates of vasorelaxation were assayed ex vivo on rat aorta segments with or without endothelium in the presence of different dilutions of fruit or vegetable juices.
Results related to total polyphenol content, antioxidant capacity and vasorelaxation were
published in two scientific articles. Red fruits clearly exhibited the highest TPC values. For all juices, a significant positive correlation was observed between TPC and the ORAC assay (r = 0.50, p = 0.02). Blackcurrant and pomegranate juices caused more than 50% inhibition of superoxide anion production in PMA-activated whole blood. The exact mass concentration (µg/mL) of each phenolic compound present in juices in the medium correlated with superoxide anion inhibition only for peonidin -3-O-glucoside (PG, r = 0.87, p = 0.010), epigallocatechin gallate (EGCG, r = 0.67, p = 0.0009), catechin (C, r = 0.47, p = 0.02) and quercetin (r = 0.46, p = 0.036) correlated with superoxide anion inhibition. Of all juices, blackcurrant ones, known for their high polyphenol content, showed the highest
capacity to induce vasorelaxation at 1% v/v, in the presence but not in the absence of
endothelium. According to the mass concentration, kaempferol, EGCG, delphinidin -3-O glucoside (DG), delphinidin -3-O-rutinoside (DR), Cyanidin -3-O-rutinoside (CyR) and PG
correlated with the vascular activity of the juices. However, concentrations of DR, CyG and in a less extent of PG required for inducing ex vivo vasorelaxation where higher than those
detected in blood plasma. More detailed in vivo studies are now required to determine if the concentrations found in the blood after ingestion of juices have direct effects on antioxidant capacity and endothelial function.