15C-13 |
Simultaneous determination of flavanols (catechins), theogallin, gallic acid and alkaloids in various black teas using RP-HPLC and influences of these compounds on the astringency |
O. TOKUSOGLU and M. K. Unal. Food Engineering Department, Ege University, 35100, Bornova,İ zmir, TURKEY., Izmir, 35100, Turkey Flavanols (catechins) in black tea are the major source of antioxidants in the human diet and has anticarcinogenic and antiarteriosclerotic effects on human health. It is established that polyphenols and methylxanthines (alkaloids) account for the astringent taste. The objectives of our study were 1) the effectively simultane determination of individual six catechins, gallic acid, theogallin (gallic acid ester), three alkaloids in black tea infusions using High Performance Liquid Chromatography (HPLC) with UV dedection 2) the optimization of isocratic elution procedure for this determination 3) to determine the influences of these compounds on the astringency taste. Twenty-three commercial black teas and tea bags were obtained from Turkish Tea Board Çaykur, Lipton, Ulusoy Company and Seylan black teas obtained from Hey Gıda A.Ş. in Turkey. After tea -water extract preparation, an optimized isocratic HPLC procedure using Hypersil-ODS column with methanol /three distilled water / formic acid (19.5 /80.2 / 0.3 v/v/v) as a mobile phase and UV dedection at 280 nm was used for separation. 8- member trained sensory panel judged black tea infusions for astringency taste. Standard compounds had linear calibration curves through the origin (R2=0.9997). The total flavanol content of different black tea infusions varied from 1,423 to 12,051 mg/100mg. Individual flavanol levels were determined as catechin (C) , epicatechin (EC), epigallocatechin (EGC), epicatechin (ECG), epigallocatechingallate (EGCG). EGCG was the major catechin in all black teas (0,356-5,972 mg/100mg) (p<0.01). Caffeine levels were very high (p<0.01) followed by theobromine and theophylline . Black tea infusions contained 0,134 -1,392 mg/100mg of GA whereas 0,156 -1,241 mg/100mg of its ester (5-O-galloyl-quinic acid). The correlation between the total catechins and astringency ( y=1,675 + 6,631 ln X) ( R2=0,9551) were extremely high at 95% confident skala (X=total catechin, y=astringency) and totaly interactions on the astringency were obtained.
Session 15C, Food Chemistry: Food composition and analysis
|