Quantitative spot test analysis of soluble tannin in green tea using a portable diffuse reflectometer Marcelo B. Lima, a St  efani Iury E. Andrade, a Inaka ˜ S. Barreto, a Luciano F. Almeida, a Edvan C. Silva a and M ario C. U. Ara ujo * ab Received 10th April 2012, Accepted 5th May 2012 DOI: 10.1039/c2ay25361e The study proposes a low cost and very simple quantitative spot test technique for determination of soluble tannin in green tea samples using a portable diffuse reflectometer. The lab-made instrument was made of polytetrafluoroethylene (PTFE), using a light emitting diode (LED) for its light source, and a phototransistor as the detector. The proposed method measured diffuse reflectance from a complex formed by reaction between soluble tannin and ferrous tartrate in a buffered medium at pH 6.8. The spot test is a reliable and advantageous alternative technique because it uses fewer chemicals than the reference method. The study obtained good limits of detection (0.11 mg L 1 ), and precision (RSD ¼ 0.9%), and at a 95% confidence level (paired t-test) no statistically significant difference between the results of either method was found. Introduction Tannins have been defined as naturally occurring, structurally complex, water-soluble secondary metabolites having molecular masses in the range 500 to at least 3–4000 and which possess 12– 16 phenolic hydroxyls and 5–7 aromatic rings per 1000 relative molecular mass. 1 They are astringent and have the natural ability to complex with various macromolecules such as proteins, starch, cellulose, and minerals. 2 Tannins in general have anti- oxidant, anti-carcinogenic, anti-mutagenic and antimicrobial activities and can assist in the prevention and treatment of diseases. 3 Green tea is appreciated by people around the world and is derived from the infusion of twigs and dried leaves of Camellia sinensis. 4 The major phenolic components in green tea are the flavanols and flavanol gallates, accompanied by flavonol glyco- sides, theogallin, traces of chlorogenic acids and proanthocya- nidins. The proanthocyanidins are the true tannins. 5 Quality control is of course important for the tea consumer, but the Marcelo B: Lima Marcelo Batista de Lima grad- uated in Chemistry at the Insti- tuto Federal de Educac ¸a˜o, Ci ^ encia e Tecnologia da Para ıba (IFPB, Joa˜o Pessoa, PB, Bra- zil) in 2008. He is also a doctoral student of Analytical Chemistry at the Universidade Federal da Para ıba (UFPB, Joa˜o Pessoa, PB, Brazil). He currently is a member of the Laborat  orio de Instrumentaca˜o e Automaca˜o em Qu ımica Anal  ıtica/Quimiome- tria (LAQA). His main areas of interest are automation and analytical instrumentation. St efani Iury E: Andrade St efani Iury E. de Andrade received a B.S. degree in Indus- trial Chemistry from Uni- versidade Federal da Para ıba (UFPB, Joa˜o Pessoa, PB, Bra- zil) in 2010. He is a doctoral student of Analytical Chemistry at the Universidade Federal da Para ıba (UFPB, Joa˜o Pessoa, PB, Brazil). Currently he is a member of the Laborat  orio de Instrumentaca˜o e Automaca˜o em Qu ımica Anal  ıtica/Quimio- metria (LAQA). His main areas of interest are automation and analytical instrumentation. a Universidade Federal da Para ıba, Departamento de Qu ımica, Joa˜o Pessoa, PB, Brazil b Department of Chemistry, CCEN, Federal University of Paraiba, Caixa Postal 5093, CEP 58051-970 Joao Pessoa, Brazil. E-mail: laqa@ quimica.ufpb.br; Fax: +55 83 3216 7437; Tel: +55 83 3216 7438 This journal is ª The Royal Society of Chemistry 2012 Anal. Methods, 2012, 4, 2329–2333 | 2329 Dynamic Article Links C < Analytical Methods Cite this: Anal. Methods, 2012, 4, 2329 www.rsc.org/methods PAPER