Sensory-directed isolation and identification of an intense salicin-like bitter compound in infected teas with bird's eye spot disease.

Teas infected with bird's eye spot disease generally exhibited a lingering and long-lasting, salicin-like bitter taste, which was unpalatable to consumers. Sensory-directed isolation processes have been performed in this study to investigate the salicin-like bitter compounds in infected teas. Results showed that infected teas were extracted using a 70% methanol aqueous solution to produce methanol extract, which was then further separated by sequential solvent extraction (SSE) to obtain dichloromethane extract, which contained the salicin-like bitter compounds. The dichloromethane extract was then isolated by flash chromatography to produce two salicin-like bitter fractions, eluted using 60% and 65% methanol aqueous solution. Finally, these two salicin-like bitter fractions were analyzed by RP-HPLC using 60-68% and 70-75% methanol aqueous solution, respectively, affording the location of the salicin-like bitter compounds in RP-HPLC chromatograms. Moreover, a new ursane-type triterpenoid, camellisin A methyl ester, was identified from infected teas. This study has provided preliminary isolation methods of salicin-like bitter compounds from the infected teas, which were essential to designing targeted debittering strategies for infected teas and improving the quality of the finished tea and the effective utilization of fresh tea leaves.

Characterization of triterpenoids as possible bitter-tasting compounds in teas infected with bird's eye spot disease.

Tea infected with bird's eye spot disease generally imparts a long-lasting bitter taste, which is unacceptable to most consumers. This study has comprehensively evaluated the taste profiles of infected and healthy teas and investigated their known bitter compounds previously reported in tea. Quantification analyses and calculation of dose-over-threshold (DoT) factors revealed that no obvious difference was visualized in catechins, caffeine, bitter amino acids, and flavonols and their glycosides between infected and healthy tea samples, which was also verified by principal component analysis (PCA) and hierarchical cluster analysis (HCA). Therefore, these known bitter compounds have been ruled out as critical contributors to the long-lasting bitterness of infected teas. Furthermore, Gel permeation chromatography, sensory analysis, and UPLC-Q-TOF-MS were employed and identified 13 substances from the target bitter fractions, including caffeine, ten triterpenoids, and two oxylipins. The higher triterpenoid levels were supposed to be the reason causing the long-lasting bitterness. This study has provided a research direction for the molecular basis of the long-lasting bitterness of infected tea leaves with bird's eye spot disease.

Characterizing relationship between chemicals and in vitro bioactivities of teas made by six typical processing methods using a single Camellia sinensis cultivar, Meizhan.

Processing method is considered as a major factor that affects biotransformation of phytochemicals in tea and leads to diverse flavor and bioactivity of tea. In the present work, six typical tea manufacturing processings were employed to compare the effect on chemical composition of teas through using leaves of the single tea cultivar - - Camellia sinensis var. Meizhan. And in vitro antioxidant activity, inhibition against α-glucosidase and three lipid metabolism enzymes of these teas were also investigated, the relationships among them were analyzed further. As fresh leaves were processed into six categories of teas, the content of total catechins (TCs) has decreased in varying degrees while theaflavins (TFs) has increased. The antioxidant capacity composite index (ACCI) from high to low were green tea, yellow tea, oolong tea, white tea, dark tea, and black tea with the range from 98.44 to 58.38, which dominated by the content of TCs. Furthermore, all categories of teas possessed an inhibition effect on the pancreatic lipase (PL), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-COA reductase), lecithin cholesterol acyltransferase (LCAT), and α-glucosidase. The inhibition rate of PL and α-glucosidase appears to be positively influenced by TFs content (r =0.863, r =0.857, p < 0.05) while that of LCAT showed significant positive correlations with the content of tea polyphonels (TPs) (r = 0.902, p < 0.01). These results provide a better understanding of the relationships between processing method and chemical components of tea. It is suggested that various tea categories possess potential healthy effects which could serve as promising nutritional supplements.[Figure: see text].

Identification of key odorants responsible for cooked corn-like aroma of green teas made by tea cultivar 'Zhonghuang 1'.

Fangping green tea (FPGT) produced by Zhonghuang 1 (C. sinensis var. sinensis cv. Zhonghuang 1), a new tea variety, has a classical cooked corn-like aroma, which is completely different from the green tea aroma. In order to illustrate the aroma characteristics of the green tea, the volatiles of FPGT was analyzed with gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O). The results showed that odor activity value (OAV) of dimethyl sulfide (DMS) was 1195.21 and the odor intensity about DMS was 6.2 in FPGT. Aroma recombination experiment also confirmed the important contribution of DMS to cooked corn-like aroma. Aroma character impact (ACI) values of DMS in tea processed by Zhonghuang 1 and Fudingdabai were 72.01% and 37.86%, respectively. This indicated that the high proportion of DMS was the dominant character of green tea with cooked corn-like aroma. In addition, the S-methylmethionine (SMM) content in fresh leaves of Zhonghuang 1 (0.21 mg/g) was significantly higher than that of Fudingdabai (0.16 mg/g), which was an important reason for high DMS content.

Effects of withering on the main physical properties of withered tea leaves and the sensory quality of congou black tea.

To explore the relationship between the moisture content of withered tea leaves and their physical properties (i.e., elasticity, plasticity, flexibility, and texture) during withering, texture analyzer was employed to test the elasticity and flexibility of withered tea leaves with different moisture contents. The texture was evaluated by computer vision technology. The withered tea leaves with different moisture contents were used to process congou black tea, which was then subjected to sensory evaluation. Results showed that good elasticity, optimal flexibility, and plasticity were achieved when the moisture content of the withered tea leaves of Fudingdabai comprising two leaves and one bud varied arranging from 65.51 to 61.48%. The sensory evaluation of congou black tea revealed that moderate withering was better than long-term withering and that both moderate and long-term withering were better than no withering during processing. The moisture content was significantly correlated with the flexibility and plasticity of the withered tea leaves. Fresh tea leaves undergoing moderate withering with moisture content of 65.51-61.48% to process congou black tea, good tea shape and liquor color were achieved. This study provided new evidence that the moisture content of withered tea leaves significantly affected the quality of black tea.

Effects of Pu-erh tea aqueous extract (PTAE) on blood lipid metabolism enzymes.

Disorders of blood lipid metabolism are the primary risk factors for many diseases. Recently, the effect of Pu-erh tea on blood lipid metabolism has received increasing attention. However, the mechanism underlying its ability to regulate blood lipid metabolism is unclear. We set out to study this through assessing the effects of Pu-erh tea aqueous extract (PTAE) on the central enzymes of blood lipid metabolism, including lipoprotein-associated phospholipase A2 (Lp-PLA2), lecithin: cholesterol acyltransferase (LCAT), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) and pancreatic lipase (PL). We find that the Lp-PLA2, HMRG and PL activities are inhibited by PTAE in a dose-dependent manner and that the LCAT activity tends to increase with increasing PTAE concentrations. Lineweaver-Burk plot analyses reveal that PTAE acts as a competitive inhibitor for HMGR and PL and as a noncompetitive inhibitor for Lp-PLA2. Moreover, we determine that its active ingredients include catechins, gallic acid, caffeine, free amino acids, and soluble sugar. However, the effect of each ingredient and whether any of them have synergistic effects are still unknown. The results suggest that Pu-erh tea has a potent ability to regulate blood lipid metabolism and knowledge of the mechanisms provides insights into its potential therapeutic application as an alternative hypolipidemic drug.