SPECIAL STORY 54 FEED & ADDITIVE MAGAZINE December 2023 Botanical extracts are natural ingredients that contain diverse polyphenol type molecules. Some are well known for their endogenous and exogenous antioxidant abilities. However, when speaking under the feed and pet food regulatory framework of the European Union so far only one natural product is registered as an antioxidant, and this is mixed-tocopherols. Some botanical extracts are registered but classified as flavoring compounds.1 This article will focus on the exogenous antioxidant capacity of rosemary and olive extracts and the main reaction mechanism of their active molecules with the highest antioxidant potential. BOTANICAL EXTRACTS: THE NEXT GENERATION OF ANTIOXIDANTS Cristina Murcia García, PhD Technical Service Manager Kemin Nutrisurance EMEA ROSEMARY EXTRACT Even if rosemary extract is well known for its great antioxidant activity for controlling oxidation of fats, oils and fat rich matrices, in feed and pet food regulation it is still classified as a flavoring compound.1 Rosemary extract contains different diterpene molecules with antioxidant activity, from these, the one with the highest antioxidant effect is carnosic acid. Other molecules such as carnosol, rosmanol or epirosmanol have also some antioxidant capacities but less significant than carnosic acid. The reason for that is that all the above are decomposition products of carnosic acid, as we will see while explaining the simplified chemical reaction mechanisms. OXYGEN SCAVENGER MECHANISM To prevent oxidation rosemary extract, or specifically, carnosic acid can scavenge singlet oxygen, an excited form of oxygen, and free radicals. While doing this carnosic acid will oxidize itself to form a carnosic acid quinone that by action of temperature or other catalysts will be transformed into carnosol. The carnosol molecule will further follow this path and will oxidise itself to be transformed into epirosmanol or rosmanol, depending on the stereochemistry of the reaction.2,3 See Figure 1. HYDROGEN TRANSFER MECHANISM Carnosic acid can also neutralize free radicals by following a different mechanism, by donating hydrogen atoms to stabilize lipid molecules (in figure 2 represented as ROOH). This type of mechanism is called hydrogen transfer mechanism. Here carnosic acid can neutralize the free radical activity of two lipid radical molecules (ROO°) to form a carnosic acid quinone. Like in the previous mechanism the carnosic acid quinone can be transformed into carnosol to provide additional antioxidant activity.
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