茶树鲜叶采前诱导和采后加工对类胡萝卜素及其衍生香气的影响

类胡萝卜素是茶叶中重要的脂溶性色素成分,也是多种关键香气物质形成的前体。利用靶标代谢组学分析方法,对茶树鲜叶中类胡萝卜素含量进行绝对定量,其总含量为(859.98±60.20)μg/g,其中叶黄素含量最高为(405.06±17.71)μg/g。制作的成品红茶中类胡萝卜素总量为(406.17±32.21)μg/g,成品绿茶中为(433.95±36.21)μg/g,与鲜叶中的含量相比,下降幅度超过50%。外源茉莉酸甲酯诱导茶树鲜叶后,鲜叶中的类胡萝卜素含量发生显著变化。利用诱导12 h后的茶鲜叶加工得到的成品红茶中的类胡萝卜素总量为(439.70±31.35)μg/g,而绿茶中类胡萝卜素总量达到(682.69±46.12)μg/g。诱导24 h后鲜叶加工制得的红茶与绿茶中14种类胡萝卜素衍生香气成分显著增加,尤其是β-大马酮,β-紫罗兰酮、香叶基丙酮以及二氢猕猴桃内酯相对含量增加>2倍。结论:利用外源茉莉酸甲酯诱导提高茶树鲜叶中类胡萝卜素含量,研究采后茶树鲜叶中类胡萝卜素在红茶和绿茶加工过程中的动态变化规律,明确诱导12 h和24 h的鲜叶制作的成品茶香气品质显著提升,类胡萝卜素含量维持在较高水平,研究结果为进一步利用外源诱导提升茶树鲜叶品质提供理论基础。

Comparison of carotenoid,chlorophyll concentrations and their biosynthetic transcript levels in different coloured cauliflower

Carotenoids and chlorophylls are among the most widely distributed pigments in nature that play essential roles in the photosynthetic apparatus and confer diverse colours in plants.Among all vegetables,cauliflower(Brassica oleracea L.ssp.var.botrytis)is rich in phytochemicals and is an important crop grown all over the world.This study investigates carotenoid and chlorophyll concentrations in differently pigmented cultivars and elucidates the role of transcriptional regulation of carotenoid accumulation including lutein andβ-carotene.Here,we characterised changes in pigments by UHPLC-DAD-ToF-MS and changes in transcript levels of carotenoid metabolic genes by qRT-PCR in florets and leaves of orange(‘Jaffa'and‘Sunset'),purple(‘Di Sicilia Violetto'and‘Graffiti'),green(‘Trevi')and white(‘Clapton')cultivars.Transcript levels of all carotenoid metabolic genes showed different transcript level patterns in the leaves and florets.Compared to the other cultivars,the orange cultivars had the highest levels ofβ-carotene in the florets and lutein in the leaves resulting in changes lutein/β-carotene ratios.In the green cultivar,higher transcript levels were also found,especially for phytoene synthase and phytoene desaturase genes of the core biosynthesis pathway.However,no increased carotenoid concentrations were observed,possibly due to a higher carotenoid turnover induced by the carotenoid cleavage dioxygenase 4 in the green cultivar.In the white(‘Clapton')and purple(‘Di Sicilia Violetto'and‘Graffiti')cultivars the phytoene desaturase transcript levels as well as carotenoid concentrations were low.Chlorophyll concentrations changed in trend comparable to the carotenoid concentrations and were only significantly lower in the leaves of the orange cultivar‘Jaffa'.Also,the chlorophyll a/b ratio changed in‘Jaffa'.In florets the highest chlorophylls concentrations were observed for the green cultivar(‘Trevi')and the purple cultivar(‘Di Sicilia Violetto').Taken together,the study demonstrates the complex source-sink relationship of carotenoid accumulation in different coloured cauliflower.

Integrated proteomic and metabolomic analyses reveal the importance of aroma precursor accumulation and storage in methyl jasmonate-primed tea leaves

In response to preharvest priming with exogenous methyl jasmonate(MeJA),tea plants adjust their physiological behavior at the molecular level.The whole-organism reconfiguration of aroma formation from the precursor to storage is poorly understood.In this study,we performed iTRAQ proteomic analysis and identified 337,246,and 413 differentially expressed proteins in tea leaves primed with MeJA for 12 h,24h,and 48 h,respectively.Furthermore,a total of 266 nonvolatile and 100 volatile differential metabolites were identified by utilizing MS-based metabolomics.A novel approach that incorporated the integration of extended self-organizing map-based dimensionality was applied.The vivid time-scale changes tracing physiological responses in MeJA-primed tea leaves are marked in these maps.Jasmonates responded quickly to the activation of the jasmonic acid pathway in tea leaves,while hydroxyl and glycosyl jasmonates were biosynthesized simultaneously on a massive scale to compensate for the exhausted defense.The levels ofα-linolenic acid,geranyl diphosphate,farnesyl diphosphate,geranylgeranyl diphosphate,and phenylalanine,which are crucial aroma precursors,were found to be significantly changed in MeJA-primed tea leaves.Green leaf volatiles,volatile terpenoids,and volatile phenylpropanoids/benzenoids were spontaneously biosynthesized from responding precursors and subsequently converted to their corresponding glycosidic forms,which can be stably stored in tea leaves.This study elucidated the physiological response of tea leaves primed with exogenous methyl jasmonate and revealed the molecular basis of source and sink changes on tea aroma biosynthesis and catabolism in response to exogenous stimuli.The results significantly enhance our comprehensive understanding of tea plant responses to exogenous treatment and will lead to the development of promising biotechnologies to improve fresh tea leaf quality.

Discrimination of Green,Oolong,and Black Teas by GC-MS Analysis of Characteristic Volatile Flavor Compounds

Tea is one of the most consumed beverages in the world and its quality is influenced by geographical origin and production methods. This study focuses on the volatile aroma components of 38 tea products from China, Japan, Indonesia, Sri-Lanka, and Chinese Taipei;among them 7 green teas, 13 oolong teas, and 18 black teas. The volatiles were extracted from the infusions using PorapakQ-resin, concentrated, and analyzed by gas chromatography-mass spectrometry. The components were identified by authentic reference compounds or preliminary based on their mass spectra. Different manufacturing processes yield different blends of aroma compounds. In general, the contents of total volatiles, aliphatics, aromatics, and terpenoids increased with the fermentation degree, whereas jasmine lactone and indole were the highest in oolong teas. Some particular manufacturing processes, for example, the use of tea leaves infested by the tea green leafhopper, lead to higher contents of volatiles in final products as in Oriental Beauty oolong tea. The relative peak areas determined for 82 volatiles were the basis for the statistical analysis and highlight the potential of multivariate analysis to distinguish tea samples of different categories.

Multiple Seasonal Modifications in Enzymatic Flavour Formation in Tea

Carotenoid cleavage enzymes isolated from Japanese Camellia sinensis leaves(cultivar Yabukita) were used for investigating the structural patterns of carotenoid cleavage enzymes.Fresh tea leaves were used for the isolation of active enzymes and purified to single band stage in SDS PAGE gels after isoelectric focusing.The specific activity of the carotenoid cleavage enzymes was tested and the active fractions selected for further analysis.The sugar content and the amount of phosphate present in the purified enzymes were elucidated by the following methods:Phosphates were detected by phosphatase assays,fluorescence marker kits and ammoniumheptamolybdate complex measurements after incineration of the samples.Sugars were detected in gels using PAS reagent(periodide acid /Schiff reagent) staining and by GC-MS after hydrolysation of the proteins with trifluoric acid.Phosphorylations as well as glycosylations of the samples could be detected in all cases,thus giving evidence for an increasing phosphorylation level of proteins in Camellia sinensis from spring(1.84 g/mg) to autumn(2.39 g/mg) as well as the presence of at least four different sugars(arabinose,xylose,galactose and ribose).These secondary modifications of the carotenoid cleavage enzymes and their dependency on the harvesting season may well correspond to the changes on the functional level which were detected between spring(Michaelis Constant(K m) =9.45 mol/l) and autumn(K m= 17.16 mol/l) harvests.