Conjugated Autoxidizable Triene-Based (CAT and ApoCAT) Assays: Their Practical Application for Screening of Crude Plant Extracts with Antioxidant Functions in Relevant to Oil-in-Water Emulsions: The CAT and ApoCAT assays for Screening of Plant Extracts

Many previous reports suggested that conventional antioxidant assays could not forecast antioxidant performance of plant extracts, especially when it came to a real food system such as oil-in-water emulsion. In this study, antioxidant activities of aqueous and ethanolic plant extracts are investigated using multiple conventional assays (TPC, ABTS, FRAP, ORAC) and the oil-in-water (O/W) emulsion-based high throughput assays (the CAT and ApoCAT) in a comparison with an autoxidative O/W emulsion model monitored by formation of lipid hydroperoxide and TBARS values. Results suggest that only the ApoCAT assay is able to forecast the antioxidative performances of the extracts in O/W emulsions, regardless of the differences in extraction solvents, while the CAT assay can explain only the performance of ethanolic plant extracts in O/W emulsions. According to untargeted metabolite analysis, the antioxidants activities of plant extracts might be strongly influenced by extraction solvents. As a result, not only is the quantity of particular metabolites impacted, but also the whole metabolite (antioxidant) profiles of the extracts are modified. In addition, this study demonstrates that both the chemical reaction scheme and physical-state of a model are important parameters for designing a better antioxidant assay in the future. Practical Applications: The ApoCAT assay would be a more practical method for screening antioxidant compounds and/or crude plant extracts than conventional antioxidant assays and the original CAT assay. The antioxidant capacity of plant extracts obtaining from the ApoCAT can be used to represent their antioxidant performances in food emulsions regardless of their extraction solvents. Several crude plant extracts using different solvents are used to validate the performance of the CAT and the ApoCAT assays in comparisons with multiple conventional antioxidant assays. These assays differ from each other in terms of scheme of reaction and physical state of the test. In addition, oil-in-water (O/W) emulsion model is used as a reference method representing the antioxidant activities in food matrices. Principal component analysis (PCA) is performed to better understand the relationship among all assays. The results suggest that only the ApoCAT assay exhibits a close relationship with O/W emulsion model in both crude ethanolic and aqueous plant extracts. Furthermore, putative metabolite profiles of crude plant extracts are identified using LC-orbitrap MS/MS.