Oxidative degradation pathways of carrot carotenes and their protection via chitosan-TPP encapsulation

Abstract

Background: Hydrogen peroxide and hypochlorous acid are reactive oxygen species that naturally occur in biological systems; the oxidation products of biological molecules, such as carotenoids, formed by these oxidants are found in foods and living organisms. This study aims to identify these metabolite products and propose the degradation mechanism based on the identified product structures and the obtained kinetic data. To protect carotenes from oxidation and improve their use as food additives and pharmaceuticals, carrot carotenoids were encapsulated in a chitosan-TPP copolymer. Results: The results revealed that the main carotene oxidation product from H<inf>2</inf>O<inf>2</inf> and HOCl was apo-13-carotenone-5,6-epoxide; LC–MS/MS also detected additional products for the first time. The kinetics study indicated that oxidation follows first-order kinetics in carotene and second-order kinetics in H2O2, with epoxidation of the ring double bonds and cleavage of the 13-double bond forming the major product, while cleavage of the single bond C10’–C11 resulted in the minor product, β-apo-12ʹ-carotenone-5,6-epoxide; proposed mechanisms were outlined. To protect carotenoids from oxidation, a chitosan-TPP complex was prepared and characterized. While free carotene stability decreased to 63% after 120 min and 34% after 30 min under H<inf>2</inf>O<inf>2</inf> and HOCl treatments, respectively, the complex remained stable at over 94% for 300 min. Additionally, the complex did not reduce the antioxidant activity of carotene against hydroxyl radicals but slightly lowered its reducing power. Carotene release followed first-order kinetics with an 88.33% recovery over nine days, mainly controlled by diffusion. Conclusion: Producing apo-13-carotenone-5,6-epoxide as a major product in carotene oxidation by both oxidants suggests that it may serve as a potential biomarker. Other new products were identified that require further study to examine their activities. The prepared chitosan-TPP complex effectively stabilizes carotenes against both ROS while retaining most of their original antioxidant activities, indicating its potential applications in the pharmaceutical and food industries.