Journal of Chromatography A, 1096 (2005) 177–186 Prediction of total green tea antioxidant capacity from chromatograms by multivariate modeling A.M. van Nederkassel a , M. Daszykowski a,b , D.L. Massart a , Y. VanderHeyden a,∗ a Department of Pharmaceutical and Biomedical Analysis, Pharmaceutical Institute, Vrije Universiteit Brussel, Laarbeeklaan 103, 1090 Brussels, Belgium b Department of Chemometrics, Institute of Chemistry, The University of Silesia, 9 Szkolna Street, 40-006 Katowice, Poland Available online 18 April 2005 Abstract In this paper, a fast strategy for determining the total antioxidant capacity of Chinese green tea extracts is developed. This strategy includes the use of experimental techniques, such as fast high-performance liquid chromatography (HPLC) on monolithic columns and a spectrophotometric approach to determine the total antioxidant capacity of the extracts. To extract the chemically relevant information from the obtained data, chemometrical approaches are used. Among them there are correlation optimized warping (COW) to align the chromatograms, robust principal component analysis (robust PCA) to detect outliers, and partial least squares (PLS) and uninformative variable elimination partial least squares (UVE-PLS) to construct a reliable multivariate regression model to predict the total antioxidant capacity from the fast chromatograms. © 2005 Elsevier B.V. All rights reserved. Keywords: Green tea; Antioxidant capacity; Monolithic columns; Warping; Aligning; Multivariate calibration; PLS 1. Introduction The dry leaves of the green tea plant Camellia sinensis (L.) are known to contain flavanols with antioxidant capacity such as catechin, (-)-epicatechin, (-)-epicatechin-3-gallate, (-)-epigallocatechin and (-)-epigallocatechin-3-gallate [1,2]. The consumption of green tea is therefore associated with protective effects against coronary heart diseases and cancers of the lung, forestomach, esophagus, duodenum, pancreas, liver, breast, colon, and skin, induced by chemical carcinogens [1]. The total antioxidant capacity of a green tea extract is an important quality criterion and can be de- termined with a decolorization assay, the Trolox equivalent antioxidant capacity (TEAC) method, in which the antiox- idant capacity is expressed as the concentration of a Trolox solution with equal antioxidant capacity [3]. Besides the flavanols, the green tea may contain many other components, also contributing to the safety and quality of the extract. To avoid a time-consuming qualitative and quantitative ∗ Corresponding author. Tel.: +32 2 477 47 34; fax: +32 2 477 47 35. E-mail address: yvanvdh@vub.ac.be (Y. Vander Heyden). analysis of each extract compound individually, fingerprint technology was introduced for quality control. Fingerprint chromatograms are developed and compared to that of a stan- dardized extract to achieve authentication, identification and quality control of the herb [4,5]. Combining the information from the green tea fingerprint and the TEAC assay allows a good determination of the quality of the tea extract. An appli- cation can be found in the paper by Koleva et al. [6], where a post-column TEAC assay is presented to measure the antiox- idant capacity of HPLC separated analytes of o.a. Rosemary extracts. However, for high-throughput applications simple and fast methods are preferred and in this paper, it is therefore investigated whether the total antioxidant capacity of green tea extracts can simply be predicted from their fast chromatograms, developed on monolithic silica columns. It was earlier shown that fast, robust and repeatable separations can be obtained at high flow rates (up to 9 ml/min) on these columns, allowing to speed up the analysis compared to conventional particle-packed HPLC columns [7]. A multivariate calibration model relating the chromato- graphic data with the TEAC data is built. A similar study but based on NIR spectra, instead of chromatograms, 0021-9673/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2005.03.102