Antioxidant and dietary products: Between truth and misconception

Abstract

Almost all dietary products (dietary supplements, food for special medical purposes,…) has a note saying that it contains antioxidants as an indispensable indication of its quality. This has become such a common practice that consumers accept it just like they accept the quality of vegetables or fruits on the market. The concept of antioxidants is far more complex than these simplified claims, especially since one important property is called negation, instead of the chemically correct one: reductant.This paper focuses on the examination of total antioxidant capacity (TAC). Eleven domestic and imported products present on the market in various pharmaceutical forms were selected. Each product was dissolved in the recommended dose – 250 mL (“standard glass of drinking water”) of deaerated demineralized water, in order to achieve a leveling effect of different drinking water composition. A solution of 500 mg of vitamin C was used as a reference substance.Three spectrophotometric methods were used to determine TAC: scavenge DPPH free radicals; Folin-Ciocalteu’s reagent reaction (total phenolic substances and flavonoids, expressed as the gallic acid equivalent) and ferric reducing antioxidant power (FRAP). Modern “green” electrochemical tests were also applied: differential pulse voltammetry (DPV) and cyclic voltammetry (CV). The results of these two methods were expressed as the vitamin C equivalent.The results prove that the statements in the materials which accompany the products or the inscriptions and the graphic representations on the packaging are, to put it mildly, more optimistic than the exact measurements prove. Thus, for example, for some classes of compounds that have redox properties (antioxidants), the stated values are several times lower in some of the tested dietary products. All the obtained results indicate the need for antioxidant properties to be normatively regulated by the introduction of mandatory testing and quantification of TAC, so that consumers would not be misled. Furthermore, L-ascorbic acid – vitamin C, a common ingredient of dietary products with antioxidant properties, is by definition a reducing agent. The emphasis on the significance of vitamin C content is relevant but it does not give a special value to a product, which is greater than, for example, 2-3 fresh red peppers. In this vegetable, not only antiscorbutic vitamin, but also reducing agents, i.e. TAC expressed as total antioxidant capacity, have the role of a “catcher” of reactive oxygen species (ROS) and accompanying oxygen radicals and they neutralize their negative effects on the body.