###### Abstract  
The supercritical CO\({}_{2}\)-based decaffeination (SCD) method can be used to prepare decaffeinated tea, but its overall effect on the phytochemicals, volatiles, and sensory qualities of green and black teas is still unclear, and its suitability to prepare decaffeinated green and black teas still needs to be compared. This study revealed the effect of SCD on phytochemicals, volatiles, and sensory qualities in black and green tea prepared from the same tea leaves, and compared the suitability of preparing decaffeinated green and black teas using SCD. The results showed that the SCD could remove 98.2 and 97.1% of the caffeine in green and black tea, respectively. However, it can cause further losses of phytochemicals in green and black teas, specifically the loss of epigallocatechin gallate, epigallocatechin, epicatechin gallate, and gallocatechin gallate in green tea and the loss of theanine and arginine in green and black teas. After the decaffeination, both green and black teas lost some volatiles but also generated new volatiles. Especially, the fruit/flower-like aroma, occimee, linaly! acetate, geranyl acetate, and D-limonene, were generated in the decaffeinated black tea, while herbal/green-like aroma, \(\beta\)-cyclodextrin, 2-ethylhexanol, and safranal, were generated in the decaffeinated green tea. The overall acceptance of decaffeinated green tea decreased due to the substantial reduction in bittermess and astringency, while the overall acceptance of decaffeinated black tea significantly increased. Therefore, SCD is more suitable for the preparation of decaffeinated black tea. 1 20  
Several factors affect the content of caffeine in decaffeinated tea, such as decaffeination technologies, tea types, and raw materials. Supercritical CO\({}_{2}\) extraction is a technique for the separation and extraction of plant components using supercritical CO\({}_{2}\) instead of conventional organic solvents. The fluid in a supercritical state has unusual phase equilibrium behavior and transfer properties with the solute in the mixture, and the solubility of the solute varies over a fairly wide range with changes in pressure and temperature, so this supercritical fluid can be used to extract specific components from a solid mixture [8; 9]. The supercritical CO\({}_{2}\)-based decaffeination (SCD) method has been widely applicated to the preparation of decaffeinated tea. [PERSON], et al. [10] removed 70.2% of the caffeine in green tea using the supercritical CO\({}_{2}\) extraction method. Still, [PERSON], et al. [11] used an ultrasonic-enhanced supercritical fluid method to remove 82.28% of the caffeine in the green tea. The SCD also removed other components in tea samples. [PERSON], et al. [12] extracted 97.4% caffeine from the green tea with supercritical CO\({}_{2}\) modified with 95% ethanol at 300 bar and 70 \({}^{\circ}\)C for 120 min, resulting in 62.2% loss of epigallocatechin gallate (EGCG). [PERSON], et al. [13] optimized the SCD for the extraction of caffeine using response surface methodology, and they extracted 95.6% caffeine from the green tea with supercritical CO\({}_{2}\) and water modified at 300 bar and about 60 \({}^{\circ}\)C for 7.5 h, resulting in only 19.8% loss of catechins. From this, it is clear that the extraction of caffeine using SCD inevitably leads to the extraction of other substances, including catechins. Meanwhile, the SCD method may reduce the volatile compounds in green tea, which may affect the aroma qualities of green tea [14; 15]. Thus, it is clear that the sensory qualities of teas could be changed after the extraction. However, the comprehensive alterations in phytochemical composition, volatile components, and sensory qualities of decaffeinated green and black teas are uncovered.