外源茉莉酸甲酯诱导茶树鲜叶及其采后乌龙茶加工关键工序中七种脂溶性色素变化

[目的]系统开展外源茉莉酸甲酯诱导以及做青阶段机械损伤双重胁迫下茶叶中脂溶性色素的动态变化研究,阐明外源茉莉酸甲酯诱导后茶树鲜叶制得乌龙茶中类胡萝卜素含量提高的机理,为合理利用外源诱导提升鲜叶品质和加工制得的乌龙茶品质提供科学依据.[方法]0.25％外源茉莉酸甲酯喷施3—4年生盆栽'金萱'茶树叶面,至均匀挂滴,对不...

Changes in Lipid-Soluble Pigments in Fresh Tea Leaves Treated by Methyl Jasmonate and During Postharvest Oolong Tea Manufacturing

【Objective】The dynamic changes of lipid-soluble pigments in tea under the dual stress of exogenous methyl jasmonate induction and mechanical damage trigged during making green stage were systematically studied. It could greatly clarify the mechanism of improvement in the content of carotenoids in making oolong teas prepared from the leaves treated by methyl jasmonate. This will offer the scientific guidance applying of exogenous elicitors improving fresh tea leaves quality and the made tea quality.【Method】The 3-4-years ‘Jinxuan’ tea cultivars in greenhouse were used as plant materials, which were applied 0.25% (v/v) methyl jasmonate solution by spraying on tea leaves homogenously until it was evenly dripped. Fresh leaves under different treated time duration (0, 24, 48, and 168 h) and the responding made oolong teas were prepared using the fresh leaves. In this study, the targeted metabolomics analysis was carried out utilizing UPLC-QToFMS aiming at analysis of changes in content of lutein, β-carotene, neoxanthin, zeaxanthin, α-carotene and chlorophyll a/b. At the same time, the dynamic changes of the lipid-soluble pigments during crucial procedure “making-green” and rolling stage were monitored. Furthermore, the sensory evaluation of made oolong teas focusing on the aroma quality was investigated.【Result】The quantitative results showed that the content of lutein reached (405.06±17.71) µg·g ^-1 in fresh leaves which was the highest of all other carotenoids, however, it decreased dramatically in made oolong teas (277.36±32.72) µg·g^-1. Lipid-soluble pigments changed significantly in methyl jasmonate treated tea samples. In the first 48 h after methyl jasmonate inducement, chlorophyll a behaved significantly increased in content compared with control (0 h) in fresh leaves, successively decreased in 168 h samples. Chlorophyll b decreased in all methyl jasmonate induced samples. Lutein exhibited an apparently decreasing in 12 h samples, thus achieved improvement in content in 24 h samples. The content of β-Carotene was lower in methyl jasmonate induced samples than that in controls, especially in 12H samples, its content was 116.36 µg·g ^-1, decreased by 34.55%. In made oolong teas prepared from methyl jasmonate-induced tea leaves (12, 24 and 48 h), the content of chlorophyll a behaved significantly decrease compared with 0 h, whilst lutein prompted quite absolutely, especially in 48 h, whose content reached 377.82 µg·g ^-1. Aiming at a clear glance, the heatmaps of the content changes of the lipid-soluble pigments were prepared, and the results showed that the content of chlorophyll a decreased in all treated samples during “making-green” stage (W1-W3) comparing with the control samples. Meanwhile, chlorophyll b apparently increased after 12h duration of methyl jasmonate inducement. Besides, the changes of the carotenoids behaved more complicated. Lutein behaved a decreasing tendency in 12 h samples, however increased in 24 and 48 h samples. β-Carotene exhibited a lower content in all treated samples, thus, zeaxanthin and α-carotene maintained a higher content compared with the control samples. In the rolling stage, the above-mentioned lipid-soluble pigments changed significantly in content. With exception of β-carotene which decreased in all treated samples, lutein, neoxanthin, zeaxanthin, and α-carotene achieved a higher content in 12, 24 and 48 h samples. It was clear that chlorophyll a decreased in methyl jasmonate treated samples in rolling stage, whilst chlorophyll b increased after 12 h. Moreover, the sensory assessment confirmed the results of aroma quality promotion in made oolong teas prepared from methyl jasmonate treated fresh leaves, however with a loss of brightness and softness in the foliage fundus.【Conclusion】In conclusion, the content of carotenoids in fresh tea leaves and the made oolong tea were absolutely improved within 24 h time duration after methyl jasmonate treatment. It was confirmed that the aroma quality was improved in made oolong tea prepared from MeJA-treated fresh leaves after 12 h which was in rich of fragrancy flavor. Differential accumulation of lipid-soluble pigments was primed under the dual stress of exogenous methyl jasmonate induction and mechanical damage trigged during “making-green” stage.