Chiang Mai J. Sci. 2015; 42(3) 699 Chiang Mai J. Sci. 2015; 42(3) : 699-711 http://epg.science.cmu.ac.th/ejournal/ Contributed Paper Determination of the Effects of Adding Milk and Sugar on the Antioxidant Capacity of Oolong Tea by Chemical and Cell Culture-Based Antioxidant Assays Angkana Wipatanawin*[a], Sudarat Phongsawanit [b], Thadthanan Maneeratprasert [b], Sittiwat Lertsiri [c] and Pawinee Deetae [b] [a] Division of Biochemistry and Biochemical Technology, Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand. [b] Food Technology Program, Mahidol University, Kanchanaburi Campus, Saiyok, Kanchanaburi 71150, Thailand. [c] Department of Biotechnology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand. *Author for correspondence; e-mail: angkana.s@cmu.ac.th; s.angkana@gmail.com Received: 22 July 2014 Accepted: 27 October 2014 ABSTRACT The effect of sugars and/or milk on the antioxidant capacity of Oolong tea was evaluated using 2,2′ -azino-bis 3-ethylbenzothiazoline-6-sulfonic acid diammonium salt (ABTS), ferrous ion-chelating (FIC) and cellular antioxidant activity (CAA) assays. The addition of sugar did not alter the antioxidant capacity of tea (p < 0.05), however with the addition of sweetener an 18% and 14% increase was observed using ABTS and FIC assays respectively. In contrast, using the CAA method, the sweetener decreased the tea antioxidant capacity by 8%. Milks and milks and sugars decreased the antioxidant capacity of tea by 30% and 45% respectively determined by ABTS and CAA assays, with an opposite result using the FIC method. The chemical and cellular based methods showed poorly correlated values. Keywords: tea, milk, sugar, sweetener, cellular antioxidant activity, FIC, ABTS, CAA 1. I NTRODUCTION Free radicals can be generated within the human body (e.g. respiratory chain) and also acquired from the environment (e.g. air pollution) [1]. Over-production of free radicals in biological systems induces cell injury by reaction with valuable molecules such as DNA, lipids and proteins [2]. This injury can lead to the development of various complications, such as chronic inflammation, cardiovascular diseases, cancers, cataracts and diabetes [3-6]. It has been reported that the consumption of fruits, vegetables and teas which contain antioxidants reduces the incidences of these complaints [7-8]. Dietary antioxidants contained in such foods promote cellular defences and prevent oxidative damage to the cellular components [9]. Among the major dietary sources of natural antioxidants, tea is one of the most concentrated in polyphenols at up to 30% of