Research Article Selective removal of caffeine from tea extracts using macroporous crosslinked polyvinyl alcohol adsorbents The hydrolysis reaction of ester groups in vinyl acetate (VAc) was used to introduce hydroxyl groups into the matrix of a macroporous adsorbent, which was itself prepared by free radical suspension copolymerization of triallyl isocyanurate (TAIC) and VAc. Therefore, the copolymerization incompatibility between the hydrophilic and the hydro- phobic monomer was overcome successfully and the hydrophobic matrix of the polymeric adsorbent containing a polyvinyl alcohol (PVA) segment was obtained. Introduction of the PVA segment decreased the hydrophobic adsorption affinity of the adsorbent while producing the hydrogen-bonding interaction. When isolating the two active components, polyphenols (TPh) and caffeine (CAF), from green tea extracts, this polymeric adsorbent, namely poly(TAIC-co-VA), exhibited good adsorption selectivity towards TPh over CAF. The adsorption mechanism leading to this selectivity involved a hydrophobic interaction mechanism for CAF and multiple weak hydrophobic and hydrogen-bonding interactions for TPh. The adsorption thermodynamics for TPh on poly(TAIC-co-VA) were studied. The effects of adsorbent structure and gradient desorption conditions on isolation were investigated. The result showed that adsorbent, with 20% TAIC content, was able to efficiently remove CAF from different tea extracts with different ratios of TPh and CAF. Finally, almost no CAF was detected in the TPh fraction and the recovery of TPh was greater than 95%. Keywords: Adsorption / Caffeine / Polymeric adsorbent / Separation / Tea polyphenols DOI 10.1002/jssc.201100598 1 Introduction The main biologically and physiologically active substances found in tea are the polyphenols (TPh) and alkaloids [1]. Of the tea TPh, catechins represent the most abundant metabolites [2], and constitute up to 30% of the mass of dry green leaves, and the molecular structures are shown in Fig. 1A. As well as being a valuable source of antioxidants in the food industry, interest in TPh has increased to medicine, health products, cosmetics, fine chemicals and other applications owing to its pharmacological effects of scaven- ging free radicals [3, 4]. Another active component in tea is a kind of alkaloid, namely caffeine (CAF), which is present in green tea at levels of around 2–5%, as shown in Fig. 1B. CAF stimulates the central nervous system, enhances immunity, strengthens the heart and induces diaeresis [5, 6]. However, excessive CAF intake can lead to adverse reactions, such as over-stimulation of the central nervous system, increased blood pressure, and it can be a risk factor for rheumatoid arthritis and premature birth. Tea TPh and CAF have their own unique pharmacological activities and the isolation of individual metabolites from tea leaf extracts allows these properties to be explored. Different methods have been used recently to success- fully separate TPh and CAF, for example, high-speed counter-current chromatography and preparative column chromatography [7–10]. However, these methods were not suitable for large-scale industrial production due to the low capacity and high production cost associated. In industrial production, tea TPh and CAF were often separated by solvent extraction [11–16], metal-ion precipitation [17] and polymeric adsorption [18–21]. Solvent extraction was a traditional and mature technique, but it was a complex process and suffers from several shortcomings including Ning Ma Peng Wang Xia Kong Rongfu Shi Zhi Yuan à Chunhong Wang Key Laboratory of Functional Polymer Materials of the Ministry of Education, Institute of Polymer Chemistry, Nankai University, Tianjin, P. R. China Received July 15, 2011 Revised September 27, 2011 Accepted September 27, 2011 Abbreviations: BV, bed volume; CAF, caffeine; PVA, polyvinyl alcohol; TAIC, triallyl isocyanurate; TPh, polyphenols; VAc, vinyl acetate à Additional correspondence: Professor Zhi Yuan E-mail: zhiy@nankai.edu.cn Correspondence: Professor Chunhong Wang, Key Laboratory of Functional Polymer Materials of the Ministry of Education, Institute of Polymer Chemistry, Nankai University, Tianjin 300071, P. R. China E-mail: wch2004@nankai.edu.cn, wangch2004@yahoo.cn Fax: 186-2223503935 & 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com J. Sep. Sci. 2012, 35, 36–44 36