Abstract: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 10~15min; However, the dark treatment remained negative value(-2.5μmol/(m2·s)), mainly conduct respiration action, and when photo synthetically active radiation was 300μmol/(m2·s), the time of withering by 30min 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 alphafarnesene 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.
