In conclusion, CAR and isoROS in rosemary diterpenoid polyphenols showed catalytic antioxidant activity in the presence of thiols. This mechanism allows CAR and isoROS to continuously exhibit antioxidant properties in the presence of thiol-containing substances as long as thiols are present. Antioxidant activity depends on the physicochemical properties of the antioxidant used. The use of catalytic antioxidants is advantageous in that their superior properties are continuously maintained during food storage. Further, two quinone derivatives, the antioxidant products of CAR and isoROS, were found to efficiently convert thiols to disulfides. Quinone substances are well known to be toxic to living organisms. This toxicity is attributed to the irreversible binding of quinones to biomaterials including protein thiol. Therefore, the mechanism of thiol addition to quinones has been extensively studied. On the other hand, the mechanism of disulfide formation by quinones is complex and not yet fully understood. Importantly, this reaction has the advantage of yielding only the original polyphenol and disulfide without producing toxic substances. In this study, an organic solvent was used as the reaction medium. However, since many foods are complex systems containing water, future research should be conducted using actual food systems. If similar results are obtained in the future studies, CAR and isoROS can act as highly effective food antioxidants and selectively form disulfide bonds through their catalytic antioxidant action. This is expected to contribute to the improvement of food texture since disulfide bonds are essential for protein cross-linking and are known to improve the physical properties of foods, such as the dough formation of flour and the gelatinization of meat proteins. ASSOCIATED CONTENT