Web Release Date: June 27,
Differentiation of Green, White, Black, Oolong, and Pu-erh Teas According to Their Free Amino Acids Content
zar,
and
Department of Analytical Chemistry, Faculty of Chemistry, University of Seville, c/Profesor García
Gonzlez, 1, E-41012 Seville, Spain, and Department of Analytical Chemistry, University of Granada,
Avda. Fuentenueva, s/n, E-18071 Granada, Spain
Received for review March 1, 2007. Revised manuscript received May 16, 2007. Accepted May 17, 2007.
Abstract:
In this paper, the differentiation of green, black, Oolong, white, and Pu-erh teas has been carried out according to their free amino acid contents. Alanine, arginine, asparagine, aspartic acid, glutamic acid, isoleucine, histidine, leucine, phenylalanine, serine, theanine, threonine, and tyrosine have been determined by liquid chromatography with derivatization with o-phthalaldehyde and fluorescence detection. The chromatographic separation was achieved with a Hypersil ODS column and gradient elution. The amino acid contents were used as chemometric descriptors for classification purposes of different tea varieties. Principal component analysis, k-nearest neighbors, linear discriminant analysis, and artificial neural networks were applied to differentiate tea varieties. Using back-propagation multilayer perceptron artificial neural networks, 100% success in the classification was obtained. The most differentiating amino acids were glutamic acid, asparagine, serine, alanine, leucine, and isoleucine.
Keywords: Tea; amino acids; reversed phase high-performance liquid chromatography; derivatization; chemometrics; pattern recognition
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