The effect of membrane-processed water on sensory properties of Oolong tea drinks

Three types of water, unprocessed water and two membrane-processed water, were employed to produce Oolong tea-drink samples. A commercial sample of Oolong teadrinks using the same materials was also included for testing. A modified quantitative descriptive analysis was conducted on a line scale by 15 trained panelists and a hedonic test was conducted by 50 naïve panelists. There were significant treatment effects on 13 out of 19 sensory descriptive attributes. The commercial sample was higher in red¯brown color and alkaline-flavor, but lower in yellow¯brown color, oolong-tea aroma, astringency, bitterness, Oolong-tea flavor, fermented-tea flavor, and astringent aftertaste. There were also membrane effects on color, aromas, and flavors of tea drinks. The most interesting phenomenon was that the unprocessed sample was found to be the lowest in the intensity of clearness by trained panelists. This implied that membrane process could improve the clearness of similar tea drinks. It was also found that 12 attributes, which could separate unprocessed, commercial and membrane-processed samples well, were important to the sensory properties of unsweetened Oolong tea drinks in principal component analysis. Concerning the preference test, the naïve panelists liked the unprocessed sample the least. It seemed that this was affected by the appearance (low clearness) of the unprocessed sample.