不同LED光质萎凋对白茶品质的影响

采用红光、黄光、绿光、蓝光和白光5种发光二极管(LED)光源开展白茶光照萎凋试验,以不照光处理为对照(CK).结果表明,光照组完成萎凋需要48 h,而CK组需要56 h.萎凋过程中白光组的多酚氧化酶(PPO)活性出现一次高峰,其他组均出现两次,而CK组PPO活性高峰出现的时间比光照组滞后6 h.蓝光组毛茶的茶多酚含量为28.43%,低于其他5组(P0.01);黄光组的氨基酸含量最高(4.35%),CK组最低(3.96%);黄光和CK组的咖啡碱含量低于其他4组(P0.05);蓝光组的黄酮类化合物含量最高(9.04 mg·g-1).试验茶样共鉴定出44种香气成分,红光组有34种,黄光组37种,绿光组23种,蓝光组31种,白光组24种,CK组24种;香气总量大小为:蓝光组白光组黄光组红光组绿光组CK组,蓝光组(0.58 mg·g-1)是CK组(0.31 mg·g-1)的1.84倍.黄光组特有的香气物质有己醛和1-壬醇;同时,黄光组的(E)-2-己烯醛、橙花醇和苯乙醇含量比其他组高,香气表现为清香带花香.LED光照萎凋对白茶外形、香气和滋味影响明显,黄光和蓝光组的形态自然、色泽墨绿、香气清鲜、滋味醇和,且黄光组的香气和滋味均带愉悦花香;绿光和白光组的香气清纯,且绿光组的滋味醇厚;红光组的香气稍带青;而CK组的外形平贴、欠匀整,香气和滋味均带青.感官审评结果表明:光照组品质均优于CK组;综合评价黄光组的感官品质最佳.

Effect of different LED lights in withering on quality of white tea

To investigate artificial illumination as withering process for high grade of aroma and taste, red, yellow, green, blue, white light emitting diode ( LED) lights at 5 levels of wavelength and illuminance and no-lighting withering as control were tested on white tea. Leaf temperature, moisture content and polyphenol oxidase ( PPO) were measured every 6 h. Aromatic constituent analy-sis and sensory evaluation were integrated for optimum tea quality. Results showed that it took 48 h to complete the withering process for LED groups while it was 56 h for the control. PPO activity peaked once in white LED group but twice in the other five groups. Peak of PPO activity for the control was 6 h after those of all the illuminated gourps. Tea polyphenols levels were significantly lower in blue group (28.43%) than the other five groups (P<0.01). Amino acids were highest in yellow group (4.35%) and lowest in the control (3.96%). Total caffeine in yellow group and the control were significantly lower than the other four groups (P<0.05). Fla-vonoid content was highest in blue group (9.04 mg??g-1). A total of 44 aromatic components were detected from 6 gourps of tea. A-mong them, 34 kinds were found in red group, 37 kinds in yellow, 31 kinds in blue, 23 kinds in green, 24 kinds in white, 24 kinds in the control. Weights of total aromatic components with the largest group in a descending were blue>white>yellow>red>green > control, with weight of blue group being 1.84 times larger than the control. Among all the groups, hexanal and 1-nonanol were only found in yellow group, and ( E)-2-hexenal, neroli, benzeneethanol in yellow group were higher than those of the other 5 groups. Moreover, sensory evaluation comfirmed that aroma from yelllow group smelled clean with flowery. Sensory evaluation com-firmed that white tea withered by yellow and blue lights were dark green and prettier in shape. They both had clean and fresh aroma, and mellow taste, especially pleasant flowery flavor was detected in aroma and taste of yellow gourp. Secondly, white tea withered by green and white lights had clean and pure aroma, though mellow taste was detected in green group. Nevertheless, mild to grassy smell were found in red group and the control, and flatter and less evenly tea-shape were found in the control. To summarize, LED light quality posed significant impact on the appearance, aroma and taste of white tea. Yellow LED light was likely to be the optimum withering illumination for best tea quality.