ISSUE FOCUS FEED & ADDITIVE MAGAZINE May 2024 53 VE (Figure 2). This thanks to their chemical redox potential value, which can be even favourably lower than the one of the latter. As such, specific types of polyphenols can also prolong the effect of VE via a synergistic interaction. Even more important is that not all polyphenols are strong antioxidants under biological conditions. How can an antioxidant be claimed to replace the (systemic) antioxidant properties of for instance VE in the animal, when it doesn’t make its way to the blood and the cells of the body tissues? That is why high values for antioxidants in classical in vitro methods (e.g. ORAC, TEAC, DPPH, FRAC) do not necessarily mean a high intra-cellular antioxidant capacity. These conventional tests typically comprise a direct oxidative challenge, induced in a test tube containing nothing but a synthetic radical solution. Needless to say, such a concept will not take into account the intestinal stability, bio-availability or intra-cellular antioxidant activity of a compound or product. HOW TO EVALUATE AN ANTIOXIDANT’S BIOLOGICAL ACTIVITY? In vitro methods with their typical shortcomings were mentioned before. So how to test a product’s antioxidant capacity in a biologically relevant way for the animal? It is important to note that live animal trials with a (small) partial replacement of VE by an antioxidant are not always ideal. This is because, within such an application, zootechnical performance is anyhow not expected to show a significant drop, as most diets are overdosed in VE. A more direct and representative way is to measure the level of Intra-Cellular Oxidative Stress (ICOS), preferably within an oxidative challenge model. This records accurately the protective effect of an antioxidant on radical-challenged animal cells (Figure 3), in terms of intra-cellular accumulation of Reactive Oxygen Species (ROS). Figure 2. From left to right: Radical neutralization and Vitamin E antioxidant recycling by polyphenols of a natural dietary blend (ELIFE®). Figure 3. From left to right: Reduced integrity and eventually death of an animal cell due to oxidative damage by generated free radicals (protective antioxidant not added).
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