乌龙茶LED补光萎凋品质特性研究

Research on Quality Characteristic Using LED as Supplementary Lighting during Withering Process in Oolong Tea

光质是乌龙茶品质形成不可缺少的环境因素,为了明确LED补光萎凋对乌龙茶品质形成的影响,选取清香型铁观音为研究对象,以无光萎凋为对照,探明日光和LED红、黄、蓝光4个光照条件下采后茶鲜叶的生理响应能力以及铁观音毛茶生化、香气组分测定与感官品质评价。试验结果表明:离体叶对不同光质的生理响应在10~15 min时分别达到峰值,光照强度为300μmol/(m^2·s)时,光照30 min可满足萎凋光环境技术参数。与无光处理相比,补光萎凋可显著提高铁观音毛茶的水浸出物、氨基酸、可溶性糖、黄酮等含量,促进了茶多酚转化并降低了咖啡碱含量;铁观音主要赋香成分α-法呢烯和橙花叔醇的相对质量分数分别提高11.42%、30.65%。主成分分析得出日光、LED萎凋处理毛茶香气质量综合得分高于无光萎凋处理,LED黄、蓝光萎凋处理香气质量综合评价略优于LED红光萎凋,并与各处理毛茶品质感官审评结果表现一致,补光萎凋技术可使经济效益提高63%。

Solar withering is the first and essential processing during Oolong tea manufacturing,which can improve and develop a pleasant scent,especially for the floral fruity scent. The traditional technology employed hot air withering in rainy days,which lacks of light radiation,the quality of Oolong tea has no fruit floral odour and the taste is niffy green and astringency. In order to make up the light waves in rainy days or instability sunlight,an artificial light source could be considered for quality improvement during withering process in Oolong tea. In this study,solar,LED（ red,yellow,blue） and dark treatments were projected for the test of physiological response, physicochemical, aroma, sensory evaluation and efficiency. Firstly,the constant temperature and humidity containing LED resource withering device for Oolong tea was developed,mainly including LED panel,air circulation channel,temperature / humidity transducer and uniform plate. The temperature / humidity transducer was applied to control the fixed conditions; Air circulation channel was projected as a medium to dehumidify and ensure the circulation of air in the box. Secondly,the test of physiological response indicated that fresh tea leaves plucking from tea plants had a limited capacity to absorb light,the net photosynthetic and transpiration rate of tea leaves increased at first and then decreased,reached peak at 10 ～ 15 min; However,the dark treatment remained negative value（-2. 5 μmol /（ m2·s））,mainly conduct respiration action,and when photo synthetically active radiation was 300 μmol /（ m2·s）,the time of withering by 30 min could be well.Thirdly, the test of biochemical component indicated that treatments exposed to different light significances increased the content of water extracts,amino acid,soluble sugar and flavones,boosted the conversion of polyphenol and decreased content of caffeine. Then,the volatile components of different treatments were assayed by chromatography-mass spectrometry detection（ GC-MS）. Principal component analysis method was used to evaluate the results. In contrast to dark treatment,the relative content of alpha-farnesene and nerolidol increased by 11. 42% and 30. 65%,respectively. The score of aroma quality exposed to solar was the highest,yellow and blue light had a bit better than red light,and dark treatment ranked the last. The sensory evaluation of quality in raw tea showed a similar trend to the results of principal component analysis. Moreover,based on light withering,the productive efficiency can be improved by 2. 6 times,the grade of tea quality increased 1 ～ 2 levels,and the economic benefit enhanced by approximately 63%. In conclusion,light can regulate and improve the taste and volatiles of Oolong tea,selecting LED as an artificial light to substitute for solar withering could be a promising technology,especially for the standardization during Oolong tea manufacturing.