Matrix effect evaluation and validation of the 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) radical cation scavenging assay, as well as its application using a tejate, an ancient beverage in Mexico

Nowadays, consumers, food industries, and researchers have a great interest in evaluating the total antioxidant value of foodstuffs and plasma samples. The 2,2 '-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation scavenging assay is one of the most common antioxidant evaluations. However, this assay shows a great variability in its methodology, e.g., the use of a phosphate buffered saline (PBS) matrix. Moreover, all prior assays did not describe a complete validation procedure. This study demonstrated that the matrix of calibration standards had a significant effect on the accuracy of antioxidant measurements, under the ABTS radical cation scavenging assay. A PBS matrix should only be used in this assay during plasma analysis due to a negative matrix effect on calibration curves. Meanwhile, a PBS-free matrix should be used during analyses of water-based beverages. Our analytical validation showed that the current assay had an inverse lineal relationship, acceptable range, sensitivity, precision, accuracy, short and long-term stability, selectivity, identity, and short time of analysis. Additionally, this study showed that a traditional Southern Mexico beverage (tejate) had antioxidant properties (inhibition of the ABTS radical cation and ability to reduce the ferric ion) due to the presence of polyphenol compounds. The biological relevance was supported by a high plasma antioxidant activity in rats after a 7-day period of tejate consumption. [GRAPHICS]