关键词: 干燥工艺；压制；重庆沱茶；风味品质；正交偏最小二乘法判别分析

Abstract: In this study, fresh tea leaves produced in Chongqing were used to made Chongqing tuo tea. We explored the effect of four drying processes, oven drying at 60 ℃ (1), oven drying at 80 ℃ (2), sun drying for 3 h followed by oven drying at 60 ℃ (3), and sun drying for 3 h followed by oven drying at 80 ℃ (4), on the flavor quality of Chongqing tuo tea and crude tea for making it. Results showed that the tuo tea and crude tea samples prepared by the former two drying methods had better sensory quality than those prepared by the latter two. The content of polyphenols was lower and only 31.3% in the crude tea prepared by the third drying process, while its contents of amino acids, water extract and aroma substances were as high as 2.2%, 43.9% and 182.57 μg/L, respectively, and 16 alkenes and 7 alcohols were identified from it. Both the number and amount of aroma compounds in the crude tea prepared by the first drying process were the highest and 54 and 190.27 μg/L, respectively, but the aroma contents in the crude tea samples prepared by the second and fourth drying methods were lower. After being compacted to obtain tuo tea, the contents of amino acids, alcohols, aldehydes, alkenes and acids in all crude tea samples decreased, while the content of caffeine increased. The contents of tea polyphenols, amino acids and water extract did not significantly change in the tuo tea sample prepared by the third drying process compared to the crude tea processed by this process, and its number and amount of aroma substances were the highest and 50 and 252.11 μg/L, respectively. In addition, its contents of ketones and esters increased by 64.6% and 113%. Two new ketones were detected in the tuo tea sample prepared by the first drying process; however, the number and amount of aroma substances in tuo tea were reduced by the second and fourth drying processes. Eleven differential aroma substances were identified by orthogonal partial least squares-discriminant analysis (OPLS-DA), which included five alkenes. The first and third drying processes provided more differential aroma substances from crude tea, and the content of n-heneicosane was high in the tuo cha prepared by the two processes. The odor activity value (OAV) of β-ionone was above 10 in all tea samples, and the OAV of linalool was above one in the tuo tea and crude tea prepared by the first and third drying processes. In summary, the quality of crude tea and tuo tea prepared by the first and third drying processes was better, and so the drying processes were more suitable for Chongqing tuo tea processing.

Key words: drying process; compacting; Chongqing tuo tea; flavor quality; orthogonal partial least squares-discriminant analysis