15C-15 |
Spectrophotometric determination of tannin levels of Turkish and Seylan black teas using iron (III) and 1,10-phenanthroline |
O. TOKUSOGLU and M. K. Unal. Food Engineering Department, Ege University, 35100, Bornova,İzmir, TURKEY., Izmir, 35100, Turkey Tannins naturally occur in plant foods and divided into two groups, the condensed tannins that are derivatives of catechin compounds, and the hydrolysable tannins, that are esters of sugars. The dark color and astringent taste of foods is generally ascribed to tannins. Black tea containing high level of tannins is the widely consumed non-alcoholic beverage not only in Turkey but also all over the world. Current tannin determination methods are colorimetric (such as Folin-Dennis),volumetric, gravimetric, protein precipitation and other mixed procedures. The objectives of our study were 1) the determination of tannin levels in Turkish and Seylan black tea infusions using UV-vis spectrophotometric method based on reduction of Fe (III) to Fe (II) by tannins (gives blue-black color) and then reacting Fe (II) with 1,10-phenanthroline to form a orange-red colored complex exhibiting UV-vis absorbsion at 540 nm. 2) to correlate between the tannin data and astringeny scores of these black teas obtained with sensory panel. Twenty-three commercial black teas, instant black teas, manufacturing pure black tea samples were obtained from Turkish Tea Board Çaykur, Lipton, Ulusoy Company and Seylan black teas obtained from Hey Gıda A.Ş. in Turkey. Trained sensory panel with 8-member evaluated black tea infusions for astringency taste. Tannic acid standard solutions had linear calibration curves (y=0,4393x-0,0063) (R2=0,9999). The total tanen contents of different black tea infusions varied from 6.264 to 10.589 g/100g. There is no significant difference in the tannin contents of different Turkish and Seylan black teas (p<0.01). Total tanen levels of instant black teas were 9.276 -10.589 g/100g. The correlation coefficient (CC) between tannin contents and astringency taste panel data was high (R2=0,9385) as r0,01 at 95% confidence area.
Session 15C, Food Chemistry: Food composition and analysis
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