Abstract: Flushes of two leaves and a bud of tea cultivar ‘Bixiangzao’ were picked during late summer and early autumn as raw material. During the black tea processing, initial microwave drying was adopted instead of conventional initial air drying. Seventeen processing groups were set up with independent variables of microwave density, time duration and piled leaf depth. Sensory quality, taste compounds and aroma compounds of the black tea were investigated and considered as quality criteria. The results show that compared with conventional initial air drying, the black tea processed with microwave power density of 600 W, 3 min, and piled leaf depth of 2 cm had the best sensory quality. Meanwhile, it showed a significant increase in the contents of theaflavins, thearubigins, catechins, ester catechins, EGCG, amino acids, caffeine and soluble sugar (P<0.05), while presented a significant decrease in the contents of tea polyphenols and theabrowmines (P<0.05). The number of aroma compounds increased from 43 to 50. The relative contents of floral and fruit scent compounds such as linalool and phenylethanol increased significantly (P<0.05). Furthermore, several novel sweet and flower scent compounds including (Z)-3,7-dimethyl-2,6-octadien-1-ol, 2,6,6-trimethyl-1,3-cyclohexadiene-1-formaldehyde, 2,6,6-trimethyl-1-cyclohexene-1-formaldehyde, and eugenol were identified. In conclusion, the initial microwave drying benefits the quality of black tea.

Key words: tea processing, black tea, initial microwave drying, sensory quality, biochemical components