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Tea aroma greatly varies with the production date. This study investigated the aroma differences among black teas processed on different dates (March 23rd, April 8th, April 15th, April 27th, and May 7th) in the spring. A sensory evaluation showed that the black tea produced on April 15th had a strong and lasting sweet aroma and the highest score of 93.5. In total, 71 volatile compounds were identified, and alcohols were the predominant category, accounting for 60.98%. From March 23rd to May 7th, the total content of volatile compounds showed a parabolic change trend and reached its maximum on April 15th (715.27 μg/L); the flavor index first peaked on April 8th (23.25) and then gradually decreased. A multivariate statistical analysis showed that 39 volatile compounds were important, differential aroma components. An odor activity value (OAV) analysis showed that the predominant odorants were β-ionone, β-damascenone, linalool, (E)-β-ocimene, and geraniol, all with values larger than 100. The total OAVs of undesirable odorants decreased and reached their minimum (70.4) on April 27th, while the total OAVs of pleasant odorants and the ratio of pleasant/undesirable odorants showed inverse changes and reached their maximum (2182.1 and 31.0, respectively) on April 27th. Based on the significance of differences and OAVs, linalool, (E)-β-ocimene, geraniol, and (E,E)-2,4-nonadienal were considered as the key differential odorants. Combined with the sensory evaluation and the differences in aroma components, it was proposed that black teas produced around April 15th in the Hunan district are more likely to have a strong and lasting sweet aroma. This study will provide scientific guidance for the production of black tea in the Hunan district, China. [ABSTRACT FROM AUTHOR]

Summary: Polyphenol oxidase (PPO) plays an important role in tea production, and there are many studies on the enzymatic synthesis of theaflavins using PPO; however, using a purified PPO isozyme (PPOI) instead of a crude PPO enzyme to obtain monomeric theaflavin in vitro is a novel approach that has rarely been previously reported. In the present study, a tea PPOI was purified and used for the enzymatic synthesis of theaflavin monomers. Tea leaf PPOI was purified 12.90‐fold, with recovery yield of 1.30% via the sequential use of precipitation with 30%−80% saturated (NH4)2SO4, Q‐Sepharose Fast Flow anion exchange chromatography and Sephadex G‐75 gel filtration chromatography. Subsequently, PPOI was used in the enzymatic synthesis of theaflavins: under various pH, temperatures, reaction times and catechin substrate composition and concentration, only the amount of theaflavin components produced was changed, and no other theaflavin component apart from the theaflavin monomer was produced. These results highlight the importance of monomeric theaflavin synthesis using purified PPOI isozyme and provide insight into PPO in the context of tea production. [ABSTRACT FROM AUTHOR]