The Accumulation Of Flavonoids Pattern In Different Tea Plant Varieties And The Taste Characteristics And Related Biosynthesis Genes Of Flavonol Tri-glycosides

Flavonol glycosides play an important role in the color and taste of tea infusion.However,the structure and taste characteristics of abundant flavonol tri-glycosides in tea leaves are still unclear.The key factors affecting the composition of flavonol glycosides in tea and the genetic regulation mechanism are far from perfection.On the basis of optimizing the rapid detection method of flavonol glycosides,the structure and taste characteristics of the flavonol glycosides were identified by preparative chromatography,nuclear magnetic resonance and sensory evaluation experiments.The key factors responsible for the accumulation pattern of flavonol glycosides were studied through the analysis of tea samples of various cultivars and regions.The key metabolic pathways of the accumulation pattern of flavonol glycosides in tea plants were preliminarily identified,and candidate genes related to the synthesis of flavonol glycosides were screened.(1)A rapid UPLC-MS method was established and optimized for the determination of 20 flavonol glycosides in tea samples,including 4 myricetin glycosides,8 quercetin glycosides and 8 kaempferol glycosides.Polyamide pretreatment was used to develop preparation method of abundance flavonol tri-glycoside monomer in tea leaves.Four kinds of flavonol glycosides in tea were isolated and identified,including quercetin/kaempferol3-O-?-D-glucopyranosyl-(1?3)-?-L-rhamnopyranosyl-(1?6)-?-D-glucopyranoside and quercetin/ kaempferol 3-O-?-L-rhamnopyranosyl-(1?3)-?-L-rhamnopyranosyl-(1?6)-?-D-glucopyranoside.(2)Flavonol tri-glycosides had no obvious taste characteristics,but they could significantly enhance the bitterness of caffeine and show no obvious taste interaction with EGCG.The total concentration of flavonol glycosides and the concentration of caffeine influence the bitterness enhancing ability of flavonol glycosides on caffeine,while the difference of aglycone and sugar chain structure had little effect.Gargling is an inefficient method to remove the flavonol glycosides from the oral cavity because they can still enhance the bitter taste of caffeine within 5 min after gargling.(3)Accumulation patterns of tea flavonoids were mainly dependent on the genetic background of the cultivars rather than plantation locations.The accumulation patterns of flavonoids in tea varieties were significantly different: the contents of ECG and flavonol di-glycoside were higher in assamica variety,while EGCG and flavonol tri-glycoside were dominant in sinensis variety.The ratio of flavonol tri-glycoside /flavonol di-glycoside and ECG / EGCG could be used as important indicators for distinguishing the different varieties and cultivars.The content of flavonol glycosides decreased after the fresh leaves were processed into green tea,yellow tea,white tea,oolong tea and black tea,especially in black tea,because all myricetin glycosides were oxidized or degraded during the fermentation and drying stage.(4)The differentially expressed genes in different maturity leaves of 'Fuding Dabaicha'(var.sinensis)and 'Yunkang 10#'(var.assamica)were mainly enriched in primary metabolic pathways such as photosynthesis,carbon fixation,starch and sucrose metabolism,and secondary metabolic pathways like flavonoid biosynthsis and phenylpropanoid metabolism.The accumulation patterns of flavonoids in different varieties could be related to the UV-B signaling response pathway and the differential expression of genes in downstream regulation and metabolic pathway.UGT91Q1?UGTPg18?UGT72B4 and UGT87A1 might be involved in the synthesis of flavonol tri-glycosides.