Botanical Extracts: The Next Generation of Antioxidants for Pet Food

As we introduce more options for natural ingredients with antioxidant activity in pet food and rendering, our customers have asked for more information on how these botanical extracts work. Today, we’re going to dig into the science behind rosemary and olive extracts.

European Food Safety Authority Approves Rosemary Extract as a Pet Food Additive

Botanical extracts are natural ingredients that contain a diverse group of polyphenol molecules. Some are well known for their endogenous and exogenous antioxidant abilities. 

Until recently, in the European Union's regulatory framework for feed and pet food only mixed-i However, in response to the European Food Safety Authority’s (EFSA) 2022 Scientific Opinion, the European Commission has now approved rosemary extract as a feed additive for cats and dogs, in the category of antioxidants. ²

Here, we will focus on the exogenous antioxidant capacity of rosemary and olive extracts and the primary reaction mechanism of their main active molecules with the highest potential antioxidant activity.

Rosemary Extract: Enhancing Antioxidant Activity in Pet Food

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 also have 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 in Rosemary Extract

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 to form a carnosic acid quinone that will be transformed into carnosol. The carnosol molecule can be futher oxidized and transformed into epirosmanol or rosmanol, depending on the stereochemistry of the reaction.³ This is often referred to as a cascade reaction.  See Figure 1 below.

Hydrogen Transfer Mechanism in Rosemary Extract

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.  Or the mechanism can follow a different pathway and lipid radicals can be stabilized by forming an epoxy quinone. In summary, the key message here is that one molecule of carnosic acid can neutralize two lipid radical molecules.³

What is learned from the chemistry explained here is that carnosic acid can generate a variety of secondary antioxidants. This unique cascade-type process can amplify the antioxidative power of carnosic acid and hence of rosemary extract and to constitute an effective defense mechanism⁴. In sum, the main driver for the antioxidant activity of rosemary extract is carnosic acid. This means that a higher level of carnosic acid concentration in a rosemary extract correlates to enhanced  antioxidant activity. The rest of the phenolic diterpenes will also have some antioxidant activity but lower than carnosic acid because, as we have seen, they are degradation products from the carnosic acid molecule. In addition, rosemary extracts contain other antioxidants, such as rosmarinic acid, bringing more antioxidant power to the overall activity of this botanical extract.

Olive Extract: Enhancing Antioxidant Activity in Pet Food

Olive extract is another natural ingredient very well known for its health benefits and widely used for centuries in the countries of the Mediterranean region.

Apart from its health or endogenous antioxidant and antimicrobial properties, recent research has shown the potential benefit of using olive extract to provide exogenous antioxidant activity to prevent oxidation of fats, oils and fat containing matrices.

Olives extracts have seen increasing usage as an ingredient in human nutrition and there is also interest if it could be economically suitable as an ingredient for the feed and pet food industries. There are potential opportunities to utilize both the leaves and the waste of the olive fruit after production of olive oil. Both co-products are rich in polyphenols with potential antioxidant activity.

In olive extracts there are two interesting molecules for that contain potential antioxidant activity: oleuropein and hydroxytyrosol. These two catechols have shown both endogenous and exogenous free radical scavenging activity.⁵

Although both active ingredients can be found in olive leaf and fruit, olive leaves are rich in oleuropein while olive fruits main ingredient is hydroxytyrosol.

Oleuropein has shown interesting antimicrobial effects, as well as some endogenous antioxidant activity.⁶ Currently there are a number of supplements in both the human and petfood markets claiming immune system activity due to the properties of oleuropein. A technological additive to control oxidation of fats and oils, oleuropein has shown poor antioxidant activity in comparison with hydroxytyrosol and other known antioxidants.⁷

On the contrary, hydroxytyrosol has demonstrated significant exogenous antioxidant activity to prevent the oxidation of feed and pet food matrices^8-9.

Several studies have proposed the mode of action of hydroxytyrosol, mainly using a radical scavenging reaction mechanism, in which the hydroxytyrosol molecule can neutralized lipid radicals (ROO°). See figure 4.

Conclusions about Olive Extract as Source of Natural Antioxidant Activity for Pet Foods

Kemin internal test results have shown that the antioxidant activity of olive fruit extract can be enhanced by combination with other molecules with known natural antioxidant activity. Contrary to the relationship between activity of rosemary extract and carnosic acid, higher amounts of only hydroxytyrosol in an olive extract do not always correlate to better antioxidant activity.¹⁰

Several studies have demonstrated that olive fruit extract containing hydroxytyrosol shows antioxidant activity comparable to that of pure hydroxytyrosol, perhaps due to the presence of active derivatives of hydroxytyrosol and other phenolic compounds which promote synergistic effects in the extract that are not available when using the pure molecule.

Further research is needed to elucidate the mode of action of the antioxidants present in the olive extract. 

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References

¹ https://ec.europa.eu/food/food-feed-portal/screen/feed-additives/search accessed on 11th November 2023

² https://eur-lex.europa.eu/eli/reg_impl/2024/1068/oj - Commission Implementing Regulation (EU) 2024/1068 of 12 April 2024.

³ T. Masuda, Y. Inaba, Y. Takeda, J. Agric. Food Chem, 2001,49,5560-5565;; S. L. Richheimer, M. W. Bernart, G. A. King, M. C. Kent, D. T. Bailey, J. Am. Oil. Chem. Soc. 1996, 73, 507-514;

⁴ M. Loussouarn, L. Krieger-Liszkay, A. Bily, S. Birtić, M. Havaux, Plant Physiol. 2017 Nov;175(3):1381-1394

⁵ M. Fiorini, V. Crognaletti, O. Sabry, P. Fattori, Processes 2021, 9, 433.

⁶ D. Borjan, M. Leitgeb, Molecules 2020, 25, 5946

⁷ M.H. Gordon, F. Paiva-Martins, M. Almeida, J. Agric. Food Chem., 2001, 49, 2480-2485

⁸ A.Y. V. Theah, T. O. Akanbi, Antioxidants 2023, 12, 929

⁹ L. Martínez-Zamora, R. Peñalver, G. Ros, G. Nieto, Foods. 2021 Oct 28;10(11):2611

¹⁰ Kemin R&D internal results