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Abstract

Tea aroma is one of the most important factors affecting the character and quality of tea. Recent advances in methods and instruments for separating and identifying volatile compounds have led to intensive investigations of volatile compounds in tea. These studies have resulted in a number of insightful and useful discoveries. Here we summarize the recent investigations into tea volatile compounds: the volatile compounds in tea products; the metabolic pathways of volatile formation in tea plants and the glycosidically-bound volatile compounds in tea; and the techniques used for studying such compounds. Finally, we discuss practical applications for the improvement of aroma and flavor quality in teas.

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... Furthermore, the accumulation of gallic acid was also influenced by the oxidative degradation of phenolic esters [38]. Decreasing shikimic acid content with increases in withering time was thought to be linked to its contribution to the synthesis of L-phenylalanine [39]. Tea aroma compounds are not always present in free form; some are in glycosidically bound form, so-called glycosides, which are more soluble in water but are less reactive than their corresponding aglycone (non-sugar part), and glycosides also synthesize volatile compounds in the presence of glycosidase during tea manufacture [39]. ...
... Decreasing shikimic acid content with increases in withering time was thought to be linked to its contribution to the synthesis of L-phenylalanine [39]. Tea aroma compounds are not always present in free form; some are in glycosidically bound form, so-called glycosides, which are more soluble in water but are less reactive than their corresponding aglycone (non-sugar part), and glycosides also synthesize volatile compounds in the presence of glycosidase during tea manufacture [39]. Alcoholic aroma compounds in black tea are often derived from glycosides and β-primeveroside; although β-primeveroside is about three times more abundant than β-glucoside, β-primeveroside decreases more than glucoside, which means that primeveroside highly contributes to the aroma formation of tea [40]. ...
... Alcoholic aroma compounds in black tea are often derived from glycosides and β-primeveroside; although β-primeveroside is about three times more abundant than β-glucoside, β-primeveroside decreases more than glucoside, which means that primeveroside highly contributes to the aroma formation of tea [40]. It was found that the withering process triggers stressful conditions for the fresh leaves, then β-primeverosidase and β-glucosidase residing in the cell wall become in contact with their respective substrates (β-primeveroside and β-glucoside, respectively) residing in the vacuole [39][40][41]. ...
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The present study emphasizes the effect of withering time set at 4 ± 0.5 h (WT4), 6 ± 0.5 h (WT6), 8 ± 0.5 h (WT8), 10 ± 0.5 h (WT10), and 12 ± 0.5 h (WT12) on the sensory qualities, chemical components, and nutritional characteristics of black tea. The sensory evaluation revealed high total quality scores at WT8 and WT10. Polysaccharides, amino acids, and soluble sugars significantly increased with an increase in withering time, and an apparent peak value was obtained at WT10. However, polyphenols, flavonoids, glycosides, organic acids, catechins, alkanoids, and theaflavins decreased with an increase in withering time. With an increase in withering time, the content of aromatic substances showed a trend of increasing first and then decreasing. The peaks of alcohols, aldehydes, and acids appeared at 10 ± 0.5 h, 10 ± 0.5 h, and 8 ± 0.5 h, respectively. The content of esters, ketones, and hydrocarbons showed a downward trend with an increase in withering time. Aroma analysis revealed that withering time could not exceed 10 ± 0.5 h. Black tea withered up to WT10 showed enhanced inhibition of α-glucosidase and α-amylase activity with good sensorial attributes. Glucose uptake inhibition capacity increased up 6 ± 0.5 h and then decreased, while antioxidant capacity decreased with an increase in withering time. The overall results show that the 8 ± 0.5 h to 10 ± 0.5 h withering time could improve black tea quality and nutritional characteristics.
... The aroma of tea is another key factor that attracts consumers. Although the volatile compounds in tea were very minor components, only about 0.01% of the dry weight of tea leaves, they were of enormous importance to the sensory attributes and quality (Yang, Baldermann, & Watanabe, 2013). Volatile aroma compounds in tea mainly came from six chemical classes, i.e., fatty acids, terpenoids, phenylpropanoids/benzenoids, carotenoid derivatives, hydrolyzed glycosides and Maillard reaction products (Kawakami & Yamanishi, 1999). ...
... Fresh tea leaves contained low concentrations of aroma compounds, most of the aroma compounds in finished tea were produced from their precursors during processing (Feng et al., 2019;Yang et al., 2013). The conversion of nonvolatile aroma precursors into volatile aroma compounds in processed tea leaves occurred through various pathways, such as the carotenoid derivatives pathway, fatty acid derivatives pathway, terpenoid derivatives pathway, phenylpropanoid/benzenoid derivatives pathway, glycoside hydrolysis pathway, and Maillard reaction pathway (Zheng, Li, Xiang, & Liang, 2016). ...
... The aroma molecules produced during the tea manufacturing process were derived from four main precursor classes: carotenoids, lipids, glycosides, and amino acids/carbohydrates (Ho et al., 2015). Therefore, to better understand aroma formation during baking of green tea after different processing methods and from different harvesting seasons, the volatile molecules that had been identified were assigned to their precursor groups, odor descriptions, and odor thresholds (Table 1), based on literature reports (Feng et al., 2019;Ho et al., 2015;Yang et al., 2013;Zheng, Wan, & Bao, 2015). ...
Article
Seven batches of raw tea leaves, processed by different methods (steaming, pan-frying) and from two different harvesting seasons (spring, autumn), were used to investigate the effect of baking treatment on changes in the composition and content of nonvolatile and volatile compounds. The results showed that baking had a greater impact on sensory and flavor quality, which chemically modified some of taste and aroma components. The aroma concentrations of steamed teas (4,168-10,706 μg/L) are significantly higher than those of pan-fried teas (959-2,608 μg/L), and the aroma concentrations of baked green teas (2,608-10,706 μg/L) are significantly higher than those of unbaked teas (959-4,213 μg/L). Based on VIP>1 and ACI>1, (E, E)-3,5-octadien-2-one, hexanal, β-ionone, 5-methylfurfural, β-cyclocitral, and linalool were identified as the main aroma compounds. Chemical changes resulting from Maillard reaction were greater during baking of steamed, than pan-fried green tea. These results help improve the quality of green tea with baking.
... e aroma of tea particles during the fermentation stage consists of a wide variety of compounds such as aldehydes, ketones, alcohols, alkanes, alkenes, and esters. [6] ese compounds originate from fatty acid derivatives, monoterpenes, carotenoids, phenylpropanoids, etc. [7][8][9][10]. e most abundant aroma compounds in black tea are (E)-2-hexenal, hexanal, (E)-geraniol, linalool, linalool oxide II, benzeneacetaldehyde, linalool oxide I, benzaldehyde, methyl salicylate, and 3,7-dimethyl-1,5,7-octatriene-3ol [9,11]. e most prominent variation in the volatile compounds of black tea aroma is observed with the alcohol. ...
... eir characteristics (floral, grassy, sweet, etc.) were identified using gas chromatography-olfactometry (GC-O) [6][7][8][9]. GCMS has high sensitivity, and over 70 different chemical compounds present in tea aroma were identified in different studies [4,6,12]. However, GCMS instruments are not found in many tea factories due to the high price of the instrument. ...
... e main compounds present in tea aroma and flavor are linalool, geraniol, phenylacetaldehyde, benzaldehyde, methyl salicylate, and hexanal [7][8][9]. ese are mostly aldehydes, ketones, esters, hydrocarbons, and esters. erefore, when developing the "e-nose" system, it is important to choose sensors that are responsive to the abovementioned chemical compounds with excellent sensitivities to detect subtle changes such as "first nose" and "second nose" as practiced in the factory. ...
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The fermentation stage is vital during the black tea manufacturing process to produce the best-quality tea. The oxidation of tea biochemical compounds results in the appearance of characteristic smell peaks during the fermentation stage. These subtle changes in tea aroma are hard to detect unless one is a trained personnel. Here for the first time, we applied e-nose to monitor the fermentation process of Sri Lankan low-country tea. In this study, detection of smell peaks during fermentation was conducted by a custom-made e-nose (Digi-Nose) with four gas sensors. Singular value decomposition (SVD) is applied to eliminate the noise and dimensionality reduction in the sensor responses observed. The prediction of the time of appearance of smell peaks was conducted with a support-vector machine (SVM). Finally, theaflavin content with time was compared to validate the optimum fermentation times observed with an e-nose.
... Few studies have been performed on the application of the modified CO 2 preservation technology in tea relative to the related research on fruits. Lalel et al. [18] showed that the total amount of aroma volatiles was significantly higher (P < 0.05) in lowconcentration CO 2 (2~3%) atmosphere preservation treatment for 20−30 days than the single low-temperature treatment. ...
... The release of phenylethanol from fresh tea leaves showed a greater increase after CO 2 treatment than a single low-temperature treatment. Similar observations were reported in the processing of post-harvest mango [18] and tomato [26] . ...
... B-Glucosidase is one of the important enzymes involved in tea aroma compounds formation , which can hydrolyze hydrolysis of β-1,4glycosidic linkages and release free volatile compounds such as linalool, benzaldehyde, and methyl salicylate during tea processing (Yang, 2013). these compounds had flowery fruity fragrances and were beneficial to the aroma quality of black tea. ...
... As stated above, β-Glucosidase was involved in tea aroma compounds formation, which could hydrolyze hydrolysis of β-1,4-glycosidic linkages and release free volatile compounds such as linalool, benzaldehyde and methyl salicylate during tea processing (Yang, 2013). Our study results showed that the relatively high concentration of linalool, methyl salicylate, nerolidol was detected in "Huangyu" fresh leaves. ...
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“Yinghong 9” is a widely cultivated large-leaf variety in South China, and the black tea made from it has a high aroma and strong sweet flavor. “Huangyu” is a light-sensitive tea variety with yellow leaves. It was cultivated from the bud-mutation of “Yinghong 9” and has a very low level of chlorophyll during young shoot development. Due to chlorophyll being involved in carbon fixation and assimilation, the changes in photosynthesis might potentially affect the accumulation of flavor metabolites, as well as the quality of “Huangyu” tea. Although “Huangyu” has a golden yellow color and high amino acid content, the mechanism underlying the formation of leaf color and drinking value remains unclear. The widely targeted metabolomics and GC-MS analysis were performed to reveal the differences of key metabolites in fresh and fermented leaves between “Yinghong 9” and “Huangyu.” The results showed that tea polyphenols, total chlorophyll, and carotenoids were more abundant in “Yinghong 9.” Targeted metabolomics analysis indicated that kaempferol-3-glycoside was more abundant in “Yinghong 9,” while “Huangyu” had a higher ratio of kaempferol-3-glucoside to kaempferol-3-galactoside. Compared with “Yinghong 9” fresh leaves, the contents of zeaxanthin and zeaxanthin palmitate were significantly higher in “Huangyu.” The contents of α-farnesene, β-cyclocitral, nerolidol, and trans- geranylacetone, which were from carotenoid degradation and involved in flowery-fruity-like flavor in “Huangyu” fermented leaves, were higher than those of “Yinghong 9.” Our results indicated that “Huangyu” was suitable for manufacturing non-fermented tea because of its yellow leaf and flowery-fruity-like compounds from carotenoid degradation.
... The measured data illustrated that the alcohol contents with fruity and green flavor in HT were indeed higher than in LT, which was the main reason for its unique aroma. Meanwhile, tea aroma is not only related to the content and ratio of tea components but also shows synergistic, masking, and tone-changing effects among the components (Liao et al., 2008;Wang et al., 2020;Yang et al., 2013;Zhu et al., 2017Zhu et al., , 2021, reflecting the differences in tea flavor characteristics and sensory experience. Previous research has indicated that under the same OAV, the aroma components of floral fragrance could be easily masked by the aroma of other fragrances (Nie et al., 2019). ...
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High mountain tea (HT) is widely acknowledged as an essential resource of high‐quality tea due to its adaptation to superior ecological environments. In this study, the sensory (aroma and taste) and safety (heavy metals and pesticide residues) characteristics of HT were characterized through sensory evaluation, gas chromatography–mass spectrometry (GC‐MS), liquid chromatography–mass spectrometry (LC‐MS), flavor activity value, and risk factor analysis. The results elucidated that the aroma sensory characteristics of HT were tender and green, accompanied by sweet and slight chestnut. A total of 8 aroma compounds were identified as the primary substances contributing to the unique aroma characteristics; the difference in the ratio of "green substances" and "chestnut substances" might be the reason for different aroma characteristics in HT and LT (low mountain tea). The taste sensory characteristics of HT were high in freshness and sweetness but low in bitterness and astringency. The high content of soluble sugar (SS), nonester catechins, sweet free amino acids, and low content of caffeine and tea polyphenols were the primary reasons for its taste characteristics. Low temperature stress might be the most fundamental reason for flavor characteristics formation in HT. Furthermore, the pollution risks of 5 heavy metals and 50 pesticide residues in HT were less than 1. The complex ecosystem and low chemical control level were speculated to be the primary reasons for the high safety quality of HT. Overall, these findings provide a more comprehensive understanding of quality characteristics and their formation mechanisms in HT. In this paper, the sensory (aroma and taste) quality and safety (heavy metals and pesticide residues) quality of high mountain tea (HT) were characterized. At the same time, it was proposed that "the different content and proportion of flavor substances is the direct reason for the flavor difference between HT and LT, and low temperature stress is the main reason for the flavor substance difference between HT and LT."
... Moreover, beverages fermented by basidiomycetes can have some functional activities, such as antibacterial, immune regulation, and antioxidant (15,16). At the same time, the rich extracellular enzyme system of basidiomycetes will produce some unique flavors in beverage production (15,17,18). ...
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Green tea has distinct astringency, bitter taste, and typical green flavor because of its post-harvest treatment without withering and enzymatic oxidation. Microbial fermentation has been identified as a promising strategy that could give green tea infusion a special taste flavor. This might be linked to the metabolic transformation ability of microorganisms. In this study, starter culture of edible mushroom Pleurotus sajor-caju (oyster mushroom) was used for submerged fermentation of green tea infusion in order to improve its flavor and taste quality. The volatile profile determined by headspace solid-phase microextraction, coupled with gas chromatography mass spectrometry, showed that the contents of (Z)-2-penten-1-ol and methyl heptadienone in green tea infusion were decreased significantly by the fermentation with the basidiomycete P. sajor-caju (p < 0.01), which would alleviate the herbal and grass flavor of green tea infusion to a certain extent. Meanwhile, the contents of linalool and geraniol were increased 9.3 and 11.3 times, respectively, whereas methyl salicylate was newly produced after fermentation by P. sajor-caju, endowing the fermented tea infusion with a pleasant flower and fruit aroma. In addition, the polyphenol profile was determined using high-performance liquid chromatography equipped with ion trap mass spectrometry, and the results indicated that the contents of most polyphenols in green tea infusion decreased significantly after fermentation by P. sajor-caju. The reduction of catechins and anthocyanins in fermented green tea infusion alleviated the astringency and bitterness. Moreover, the antioxidant activity of fermented green tea infusion was obviously decreased, especially the DPPH-free radical-scavenging ability and the ferric-reducing power. However, it is noteworthy that the ABTS-free radical scavenging ability was improved compared with the unfermented one, indicating that the increased tea pigments and volatile metabolites (such as linalool and geraniol) after fermentation with P. sajor-caju may also contribute to the antioxidant capacity of fermented green tea infusion. Overall, the innovative approach driven by P. sajor-caju fermentation has achieved promising potential to manipulate the green tea flavor.
... The aroma of tea is a key index in tea quality evaluation, and the difference in tea aroma largely depends on the tea plant cultivar and manufacturing process (Ho et al., 2015;Feng et al., 2019). To date, more than 600 volatile aroma compounds have been reported during the tea manufacturing process (Yang, Baldermann, & Watanabe, 2013;Ho et al., 2015). According to the type of volatile compounds detected in tea, it is generally believed that the formation of tea aroma mainly comes from four pathways: carotenoid degradation, lipid oxidation, glycoside hydrolysis, and the Maillard reaction (Ho et al., 2015). ...
Article
Spreading is an indispensable process in the aroma formation of premium green tea. In this study, volatile metabolomics and transcriptomics were performed for three tea plant cultivars to investigate the mechanism of changes occurring in volatile compounds during green tea spreading. The content of primary aroma compounds significantly increased after spreading, the Wickremasinghe-Yamanishi ratio decreased and the Owuor’s flavor index increased with the extension of spreading time, and the degree of aroma production was genotype-dependent. Volatile terpenes and fatty acid-derived volatiles were the principal aroma volatiles that accumulated during the spreading of green tea, and the trends of their changes were consistent with the expression pattern of related synthesis pathway genes, indicating that they were primarily derived from de novo synthesis rather than glycoside hydrolysis. Two co-expression networks that were highly correlated with variations in the volatile component contents during the spreading process were identified via WGCNA. Our results provide insights into spreading that can be considered to improve the quality of green tea.
... Of the chemical components in matcha, water-soluble carbohydrates, organic acids, amino acids, polyphenols and caffeine are of particular interest as they are thought to contribute to the taste of matcha (Horie et al., 2018;Hu et al., 2012;Jakubczyk et al., 2020;. On the other hand, aroma, which is usually attributed to odour-active volatile compounds, is another important factor used in the evaluation of the green tea quality (Peng et al., 2020;Yang et al., 2013). Baba et al. (2017) reported key odourants in matcha via the use of gas chromatography-olfactometry (GC-O) while Tan et al. (2019) compared and characterised the volatiles of different Japanese green teas (sencha, matcha and hojicha). ...
Article
Analysis of three matcha (cyclone-, bead- and stone-milled) revealed differences in their sizes and surface morphologies. Using liquid chromatography, 4 sugars, 6 organic acids, 18 amino acids and 9 polyphenols were detected in all matcha samples and shown to present in different amount. Moreover, 108 volatile compounds were detected and 30 potential flavour-contributing compounds were quantified by gas chromatography time-of-flight mass spectrometry using headspace-stir bar sorptive extraction-thin-film solid-phase microextraction (HS-SBSE-TFSPME). Sensory evaluation by a trained panel found that the matcha samples possess different notes (cyclone-milled: leafy; bead-milled: fishy; and stone-milled: roasty) which is supported by the volatile compound analysis. Finally, the three matcha were differentiated based on non-volatile and volatile components using principal component analysis, and the correlation between chemical composition and sensory evaluation data was carried out using partial least square regression. In conclusion, milling processes clearly affected the physical, chemical and sensory qualities of matcha.
... Aroma formation in oolong tea mainly results from complicated manufacturing processes (Liu et al., 2018), including solar-withering, turnover, panning, rolling, and drying. To date, about 80 types of volatile aroma compounds have been identified in fresh tea leaves, while more than 300 have been found in oolong tea (Yang et al., 2013). Volatile compounds that constitute oolong aroma are divided into four classes based on their origin, namely, fatty acid derivatives, phenylpropanoids/benzenoids, terpenoids, and norisoprenoids (Fu et al., 2017). ...
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Aroma is an essential quality indicator of oolong tea, a tea derived from the Camellia sinensis L. plant. Carboxylic 6 (C6) acids and their derivative esters are important components of fatty acid (FA)-derived volatiles in oolong tea. However, the formation and regulation mechanism of C6 acid during postharvest processing of oolong tea remains unclear. To gain better insight into the molecular and biochemical mechanisms of C6 compounds in oolong tea, a combined analysis of alcohol dehydrogenase (ADH) activity, CsADH2 key gene expression, and the FA-derived metabolome during postharvest processing of oolong tea was performed for the first time, complemented by CsHIP (hypoxia-induced protein conserved region) gene expression analysis. Volatile fatty acid derivative (VFAD)-targeted metabolomics analysis using headspace solid-phase microextraction-gas chromatography time-of-flight mass spectrometry (HS-SPEM-GC-TOF-MS) showed that the (Z)-3-hexen-1-ol content increased after each turnover, while the hexanoic acid content showed the opposite trend. The results further showed that both the ADH activity and CsADH gene expression level in oxygen-deficit-turnover tea leaves (ODT) were higher than those of oxygen-turnover tea leaves (OT). The C6-alcohol-derived ester content of OT was significantly higher than that of ODT, while C6-acid-derived ester content showed the opposite trend. Furthermore, the HIP gene family was screened and analyzed, showing that ODT treatment significantly promoted the upregulation of CsHIG4 and CsHIG6 gene expression. These results showed that the formation mechanism of oolong tea aroma quality is mediated by airflow in the lipoxygenase-hydroperoxide lyase (LOX-HPL) pathway, which provided a theoretical reference for future quality control in the postharvest processing of oolong tea.
... It was also found in volatiles formation in black tea. 45 In addition, glycerolipids and glycerophospholipids degradation (i.e. MGDG 36:6, DGDG 36:6, PC 34:3, PC 36:6) contribute to characteristic flavor in oolong tea and black tea made with purple-leaf tea. ...
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BACKGROUND Lipids are one of the most important bioactive compounds, affecting the character and quality of tea. However, the contribution of lipids to tea productions is still elusive. Here, we systematically identified the lipid profiles of green, oolong, and black teas in purple-leaf tea (Jinmingzao, JMZ) and green-leaf tea (Huangdan, HD), respectively. RESULTS The lipids analysis showed regular accumulation in tea products with different manufacturing processes, among which the fatty acids, glycerolipids, glycerophospholipids, and sphingolipids contribute to the quality characteristics of tea products, including typical FA, MGDG, DGDG, and PC. Compared tea materials with products, levels of fatty acids were up-regulated, while glycerolipids and glycerophospholipids were down-regulated in tea products. FA 18:3, FA 16:0, MGDG 36:6, DGDG 36:6, PC 34:3, and PC 36:6 were the negative contributor to green tea flavor formation of purple-leaf tea. The pathway analysis of significant lipids in materials and products of purple-leaf tea were enriched linolenic acid metabolism pathway and glycerolipid metabolism. CONCLUSION This study provides insights into the lipid metabolism profiles of different tea leaf colors, and found that fatty acids are essential precursors of black tea flavor formation. This article is protected by copyright. All rights reserved.
... The volatile metabolites in Cluster 2 began to accumulate significantly 40 min after wounding treatment. Notably, indole, farnesene, E-nerolidol, and ocimene, the most important aroma components of oolong tea (Lin et al., 2013;Yang et al., 2013;Baldermann et al., 2014), were clustered in Cluster 2. In contrast to the accumulation pattern of cluster 1 and cluster 2, the volatile metabolites in cluster 3 including hexanal, (Z)-3-hexenal, (Z)-3-hexen-1-ol, cis-3-hexenyl isovalerate, (Z)-2-penten-1-ol, (E)-2-non-enal, and 1-heptanol were abundant in fresh leaves (YL stage) and began to decrease approximately 40 min after the wounding treatment ( Supplementary Figure 4 and Supplementary Dataset 2). Our results suggest that most of the substances with a grass odor such as (Z)-3-hexen-1-ol (Wang et al., 2017), 1-heptanol (Wang et al., 2017), and hexanal (Wen et al., 2014) gradually disappear within 40 min after wounding treatment, while some substances with flower and fruit flavors gradually accumulate after 40 min of wounding treatment, which may be the potential reason why it is necessary to keep tea leaves motionless after wounding treatment for a while during oolong tea possessing (Gui et al., 2015;Zeng et al., 2019a;Chen et al., 2020). ...
Article
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Understanding extensive transcriptional reprogramming events mediated by wounding during the oolong tea manufacturing process is essential for improving oolong tea quality. To improve our comprehension of the architecture of the wounding-induced gene regulatory network, we systematically analyzed the high-resolution transcriptomic and metabolomic data from wounding-treated (after turnover stage) tea leaves at 11 time points over a 220-min period. The results indicated that wounding activates a burst of transcriptional activity within 10 min and that the temporal expression patterns over time could be partitioned into 18 specific clusters with distinct biological processes. The transcription factor (TF) activity linked to the TF binding motif participated in specific biological processes within different clusters. A chronological model of the wounding-induced gene regulatory network provides insight into the dynamic transcriptional regulation event after wounding treatment (the turnover stage). Time series data of wounding-induced volatiles reveal the scientific significance of resting for a while after wounding treatment during the actual manufacturing process of oolong tea. Integrating information-rich expression data with information on volatiles allowed us to identify many high-confidence TFs participating in aroma formation regulation after wounding treatment by using weighted gene co-expression network analysis (WGCNA). Collectively, our research revealed the complexity of the wounding-induced gene regulatory network and described wounding-mediated dynamic transcriptional reprogramming events, serving as a valuable theoretical basis for the quality formation of oolong tea during the post-harvest manufacturing process.
... It was reported that caramel-like odorant furaneol is not only generated from Maillard reaction but also the hydrolysis product of bound furaneol [21]. In addition to amino acids/carbohydrates, lipids, carotenoids and glycosides are also important precursors of odorants [17,18,22]. Lipid oxidation/peroxidation leads to the generation of short fatty acids, alcohols, esters, hydrocarbons and ketones [23,24]. ...
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The yellowing process is the crucial step to form the characteristic sensory and chemical properties of yellow tea. To investigate the chemical changes and the associations with sensory traits during yellowing, yellow teas with different yellowing times (0–13 h) were prepared for sensory evaluation and chemical analysis. The intensities of umami and green-tea aroma were reduced whereas sweet taste, mellow taste and sweet aroma were increased under long-term yellowing treatment. A total of 230 chemical constituents were determined, among which 25 non-volatiles and 42 volatiles were the key chemical contributors to sensory traits based on orthogonal partial least squares discrimination analysis (OPLS-DA), multiple factor analysis (MFA) and multidimensional alignment (MDA) analysis. The decrease in catechins, flavonol glycosides and caffeine and the increase in certain amino acids contributed to the elevated sweet taste and mellow taste. The sweet, woody and herbal odorants and the fermented and fatty odorants were the key contributors to the characteristic sensory feature of yellow tea with sweet aroma and over-oxidation aroma, including 7 ketones, 5 alcohols, 1 aldehyde, 5 acids, 4 esters, 5 hydrocarbons, 1 phenolic compound and 1 sulfocompound. This study reveals the sensory trait-related chemical changes in the yellowing process of tea, which provides a theoretical basis for the optimization of the yellowing process and quality control of yellow tea.
... This is the case of terpenes and C 13norisoprenoids usually detected in green coffee, roasted coffee and coffee brews (Czerny and Grosch, 2000;Clarke and Vitzthum, 2001;Flament, 2002;Bonnlaender et al., 2004;Akiyama et al., 2008;Yener et al., 2015), and well known to impart pleasant and appreciated flowery notes to the coffee beverage (Flament, 2002;Del Terra et al., 2013). These compounds are remarkably important contributors to the aroma of a wide range of important beverages and food products as well, including fruits such as kiwifruits, mangoes, lychees and tomatoes (Sefton et al., 2011;Maicas and Mateo, 2005;Marlatt et al., 1992) as well as tea (Yang et al., 2013) and grape and wine (Flamini and Traldi, 2010). ...
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Grape aroma precursors have been extensively studied and many glycosidically-bound terpenols and C13-norisoprenoids were identified. Instead, these compounds were scarcely investigated in green Coffea arabica where just few glycosidic compounds were identified so far. By resorting to knowledge of glycoside aroma precursors in grape and the possibility to identify their structures using a high-resolution mass spectrometry database constructed for grape metabolomics, targeted investigation of glycoside precursors in green C. arabica from different geographical origins, was performed. High linalool hexose-pentose was found in all the investigated samples and hexosyl-pentoside derivatives of geraniol, linalooloxide and another linalool isomer, were identified. Moreover, two putative norisoprenoid glycosides were characterized. β-Damascenone was detected in the volatile fraction of the examined C. arabica coffees only after acid addition, however no signals of β-damascenone glycosides, were found. Findings suggests that this important aroma compound could form by hydrolysis and dehydration of a putative 3-hydroxy-β-damascone glycoside precursor identified for the first time in coffee. Aglycones released during the roasting process contribute to enrich the coffee aroma with their positive sensory notes and the identification of these glycosides can contribute to disclose the coffee biology including biochemical, physiological and genetic aspects.
... Most of the compounds showed the highest concentration at the two-or three-minute point, except for dimethyl sulfide and 2,4-di-tert-butylphenol. Volatile terpenoids are an important class of aroma-active compounds that are responsible for the flavor and fragrance of food. Linalool and linalool oxide are terpene alcohols, which have floral and lavender aromas [32]. Linalool oxide appeared to be the dominant differential compound (VIP value 2.700) present in the headspace during the green tea brewing process. ...
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Aroma substances are the most crucial criteria for the sensory evaluation of tea quality, and also key attractors influencing consumers to make the decision for purchasing tea. Understanding the aromatic properties of tea infusion during different brewing time is crucial to control the tea aromatic quality. Here, headspace and direct immersion solid-phase microextraction (HS-SPME and DI-SPME), coupled with GC-MS, were employed to investigate the impact of brewing time on the changes of the volatile features of green tea infusion. Esters, aldehydes, alcohols, fatty acids, and alkaloids were the predominant volatile groups from tea infusions. Two to three minutes was identified as the best duration for the tea brewing that can maximize the abundance of aromatic chemicals in the headspace emitted from the tea infusions. The variation of the key aromatic contributors between the tea infusion and the headspace over the infusion tended to equilibrate during the tea brewing process. This study provides a theory-based reference method by analyzing the real-time aromatic characteristics in green tea. The optimal time was determined for aromatic quality control, and the complementary relationship between the volatiles in the headspace and its counterpart, tea infusion, was primarily elucidated.
... There are many ways to extract the aroma of tea, such as headspace solid-phase microextraction (HS-SPME) [5], stir bar sorptive extraction (SBSE) [6], solventassisted flavor evaporation (SAFE) [7], and simultaneous distillation extraction (SDE) [8]. These aroma extraction methods have their advantages and disadvantages: HS-SPME can quickly extract volatile compounds, but is not particularly effective for some compounds [9]; SBSE coating has low selectivity, and it is difficult to meet the analysis requirements of complex systems; experimental results may be affected by high temperature during the SDE process [7]; and trace compounds could be extracted more accurately by SAFE [10]. So far, more than 600 volatile compounds have been detected in black tea (including black tea For the three kinds of black tea, SAFE and HS-SPME were used as two methods with different extraction principles to recover volatile compounds and obtain relatively complete results [16]. ...
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Jinjunmei (JJM), Keemun (KM), and Dianhong (DH) are the representative black teas in China, and they have always been favored by consumers. In this study, we aim to obtain the aroma characteristic information of volatile components in black tea samples through headspace solid-phase microextraction (HS-SPME), solvent-assisted flavor evaporation (SAFE), and gas chromatography-mass spectrometry combined with gas chromatography-olfactometry technology. The results showed that 70 compounds including α-methylbenzyl alcohol (isomer of β-phenylethanol) were identified as odorants. Among them, 39 compounds such as linalool and geraniol showed a high degree of aroma contribution. Furthermore, the Feller’s additive model was used to explore the perceptual interactions among the methyl salicylate and the floral compounds (10 groups) : five groups of binary compounds showed masking effect after mixing, one group showed additive effect, and four groups showed synergistic effect. The ratio (R) was compared with the aroma index (n) of Steven’s law, which found a high-fitness exponential relationship. The results of this study help to provide additional and new theoretical guidance for improving the aroma quality of black tea.
... The formation and increase of volatile compounds during storage can be either directly via oxidative degradation of precursor compounds, such as carbohydrates, carotenoids, amino acids, and fatty acids that are present or, further metabolism of primary fatty acid-derived molecules [49]. The increases observed for limonene and geranyl acetate were likely due to condensation of common precursors, isopentenyl diphosphate and dimethylallyl diphosphate, produced by carbohydrates present and acetyl coenzyme A [50,51]. ...
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Green rooibos extract (GRE), shown to improve hyperglycemia and HDL/LDL blood cholesterol, has potential as a nutraceutical beverage ingredient. The main bioactive compound of the extract is aspalathin, a C-glucosyl dihydrochalcone. The study aimed to determine the effect of common iced tea ingredients (citric acid, ascorbic acid, and xylitol) on the stability of GRE, microencapsulated with inulin for production of a powdered beverage. The stability of the powder mixtures stored in semi-permeable (5 months) and impermeable (12 months) single-serve packaging at 30 °C and 40 °C/65% relative humidity was assessed. More pronounced clumping and darkening of the powders, in combination with higher first order reaction rate constants for dihydrochalcone degradation, indicated the negative effect of higher storage temperature and an increase in moisture content when stored in the semi-permeable packaging. These changes were further increased by the addition of crystalline ingredients, especially citric acid monohydrate. The sensory profile of the powders (reconstituted to beverage strength iced tea solutions) changed with storage from a predominant green-vegetal aroma to a fruity-sweet aroma, especially when stored at 40 °C/65% RH in the semi-permeable packaging. The change in the sensory profile of the powder mixtures could be attributed to a decrease in volatile compounds such as 2-hexenal, (Z)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, (E,Z)-2,6-nonadienal and (E)-2-decenal associated with “green-like” aromas, rather than an increase in fruity and sweet aroma-impact compounds. Green rooibos extract powders would require storage at temperatures ≤ 30 °C and protection against moisture uptake to be chemically and physically shelf-stable and maintain their sensory profiles.
... 2-methoxy-furan, cis-2-(2pentenyl) furan, and 2-propyl-furan are the Maillard reaction products; the levels of 2-methoxy-furan increased in FTS, PF2, BHL, particularly in BHL, which is consistent with the results of the existing research (9), and 2-propyl-furan exhibited an upward trend in most processes but decreased in DTL and BHL. Moreover, cis-2-(2-pentenyl) furan increased in STL, FTS, and RPL, whereas it decreased in BHL significantly (p < 0.05), which contradicts the existing research that high temperature and longterm drying is conducive to the Maillard reaction (30), and may be related to the further transformation of these two substances at high temperatures. ...
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Round green tea (RGT) is widely distributed and presents a high yield in China. The quality of RGT can be determined by its aroma; however, the transformation and formation of volatile metabolites during RGT processing remain unclear. In this study, 173 volatile compounds (nine categories) were identified totally from RGT via gas chromatography-mass spectrometry with infrared-assisted headspace-solid phase microextraction. These substances exhibited different changing trends during various procedures, with the most intense transformation occurring during fixation, followed by pan-frying and second drying; moreover, 51 substances were screened, mainly containing fatty acid-derived volatiles (i.e., (E)-2-hexen-1-ol, Hexanal, pentanal, hexanal) and glycoside-derived volatiles (i.e., linalool, geraniol, benzyl alcohol, benzaldehyde), and their evolution during processing was clarified. Furthermore, the effect of the second-drying temperature on volatile compound metabolism was clarified, and 90°C was the best temperature for RGT aroma. This research lays a foundation for in-depth quality control and the aroma formation mechanism of RGT.
... Tea is popular worldwide partly due to its favorable flavor and taste (Yang et al., 2013). Aromatic aroma compounds, including volatile compounds and non-volatile compounds, contribute to tea flavor. ...
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Persimmon leaves are used for making persimmon leaf tea or as functional ingredients due to their enrichment in flavonoids, the beneficial mineral contents, and favorable flavors contributed by volatile aroma compounds. The varieties/cultivars had a significant influence on the quality and flavor of persimmon leaf tea. In this study, the integrated metabolomic-transcriptomic analysis was conducted to investigate the potential in flavonoid biosynthesis, mineral absorption, and degradation of aromatic compounds from tender leaves of “ Diospyros kaki. Heishi” (HS), “ Diospyros kaki Thunb. Nishimurawase” (NM), and “ Diospyros kaki Thunb. Taifu” (TF), using rootstock “ Diospyros Lotus Linn” (DL) as the control. The metabolomic analysis showed that 382, 391, and 368 metabolites were differentially accumulated in the comparison of DL vs. HS, DL vs. NM, and DL vs. TF, respectively, and 229 common metabolites were obtained by comparative analysis. By RNA sequencing, 182,008 unigenes with 652 bp of mean length were annotated and 2,598, 3,503, and 3,333 differentially expressed genes (DEGs) were detected from the comparison of DL vs. HS, DL vs. NM, and DL vs. TF, respectively. After the Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment, 6, 6, and 3 DEGs [with | log2(fold change)| ≥ 1 simultaneously in the three comparisons] involved in flavonoid biosynthesis, mineral absorption, and degradation of aromatic compounds, respectively, were selected for quantitative reverse transcription-polymerase chain reaction (qRT-PCR) validation and the consistent trends of the relative expression level of each DEG with RNA sequencing (RNA-seq) data were observed. Based on the transcriptomic analysis and qRT-PCR validation, it was observed that the leaves of HS, NM, and TF had the greatest level of mineral absorption, flavonoid biosynthesis, and degradation of aromatic compounds, respectively. In addition, a positive correlation between the 15 DEGs and their metabolites was observed by the conjoint analysis. Thus, the tender leaves of HS, NM, and TF could be recommended for the production of persimmon leaf tea rich in mineral elements, flavonoid, and aroma compounds, respectively.
... The various aroma-types, such as chestnut-like, cooker corn-like, orchid-like and clean aroma, might be resulted from the differences of the OAVs for volatile compounds in the green teas [18][19][20]48]. Table 4 also showed that the key odorants in the XYMJ green teas and other green teas almost belong to endogenous biosynthesis volatiles, including fatty acid derived volatiles (FADVs), amino acid derived volatiles (AADVs), volatile terpenes (VTs) and carotenoid derived volatiles (CDVs) [49,50]. It is reported that most FADVs presented a fresh or green odor. ...
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Xinyang Maojian (XYMJ) green tea is one of the top ten teas in China, and the consumers prefer spring tea due to its umami taste and pleasurable aroma. However, the knowledge about temporal variation of the volatile compounds in XYMJ green teas harvested during different seasons is very limited. In the present work, the main non-volatile compounds that endowed the taste and volatile compounds responsible for the aroma in XYMJ green teas harvested during the spring and autumn seasons were determined. The average contents of free amino acids (FAA) were significantly higher and gradually declined in the spring teas, whereas the caffeine was significantly lower and gradually increased in the spring teas. A total of 39 volatile compounds of six chemical classes were detected in XYMJ green teas, and they displayed various change trends during the spring and autumn seasons, among which 15 volatile compounds were identified as the key odorants based on odor activity value (OAV). The highest OAV of 2195.05 was calculated for the violet-like smelling trans-β-ionone followed by decanal, nonanal, dimethyl sulfide, linalool, geraniol and naphthalene. The OAVs of geraniol, (Z)-3-hexenyl hexanoate, heptanal, benzaldehyde and hexanal in XYMJ spring teas were higher than XYMJ autumn teas. The hierarchical clustering analysis indicated that XYMJ green teas were divided into three clusters and the quality of XYMJ green teas changed greatly within spring season. Harvest season is a crucial factor affecting the flavor quality of XYMJ green teas.
... Most of volatile compounds were formed by the enzymatic, hydrolysis and thermal cracking reactions in the mechanical damage and high temperature of leaves during processing [9]. Many alcohol volatiles are reported to release from glycoside-bonded molecules by hydrolyzing during withering [21]. Relatively long time of pan-fire fixation may cause alcohols with low boiling point to volatilize and promote the formation of esters by esterification reaction of alcohols and acids. ...
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Fixation is a key process contributing to different flavors of green tea and pan-fire and steam were the common fixation methods applied conventionally. In this study, pan-fired green tea (PGT) and steamed green tea (SGT) produced by different fixation methods were compared in characteristic biochemicals including volatile compounds, amino acids, catechins and alkaloids, together with evaluating their tastes and lipid-lowering effects. PGT and SGT could be distinguished clearly by orthogonal partial least squares discriminant analysis (OPLS-DA) and heatmap. SGT had higher contents of volatile alcohols (44.75%) with green and floral attributes, while PGT had higher contents of volatile esters (22.63%) with fruity and sweet attributes. Results of electronic tongue analysis showed that PGT and SGT had similar taste of strong umami and sweetness, but little astringency and bitterness. In addition, amino acids were more abundant in PGT (41.47 mg/g in PGT, 33.79 mg/g in SGT), and catechins were more abundant in SGT (111.36 mg/g in PGT, 139.68 mg/mg in SGT). Zebrafish larvae high-fat model was applied to study the lipid-lowering effects of PGT and SGT. Results showed that both SGT and PGT had lipid-lowering effects, and the lipid level was decreased to 61.11 and 54.47% at concentration of 300 mg/L compared to high-fat group, respectively. Generally, different fixation methods of pan-fire and steam showed significant effects on aroma and contents of characteristic chemical compounds (amino acids and catechins) of green tea, but no effects on the taste and lipid-lowering activity.
... These substances presented floral, fruity, and delicate aromas [4,7], and the increase in their content might contribute to the formation of the floral and fruity aromas of black tea. Benzaldehyde and benzyl alcohol were products of the shikimate pathway, which were produced by phenylalanine under the action of phenylalanine decarboxylase [49]. They had sweet, fruity, and citrus-like aromas and were reported to be the main aldehyde in black tea [50]. ...
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Changes in key odorants of shaken black tea (SBT) during its manufacture were determined using headspace solid-phase microextraction (HS-SPME) combined with comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC × GC–TOFMS) and multivariate data analysis. A total of 241 volatiles was identified, comprising 49 aldehydes, 40 esters, 29 alcohols, 34 ketones, 30 aromatics, 24 alkenes, 17 alkanes, 13 furans, and 5 other compounds. A total of 27 volatiles had average relative odor activity values (rOAVs) greater than 1, among which (E)-β-ionone, (E,Z)-2,6-nonadienal, and 1-octen-3-one exhibited the highest values. According to the criteria of variable importance in projection (VIP) > 1, p < 0.05, and |log2FC| > 1, 61 discriminatory volatile compounds were screened out, of which 26 substances were shared in the shaking stage (FL vs. S1, S1 vs. S2, S2 vs. S3). The results of the orthogonal partial least squares discriminate analysis (OPLS-DA) differentiated the influence of shaking, fermentation, and drying processes on the formation of volatile compounds in SBT. In particular, (Z)-3-hexenol, (Z)-hexanoic acid, 3-hexenyl ester, (E)-β-farnesene, and indole mainly formed in the shaking stage, which promoted the formation of the floral and fruity flavor of black tea. This study enriches the basic theory of black tea flavor quality and provide the theoretical basis for the further development of aroma quality control.
... The aroma compounds in black tea infusion depended on the glycoside aroma precursor in the black tea leaves, and were also related to the activity of glucosidase. These factors were all related to the origin of the black tea, the soil, climate, and the type of tea tree [37]. Tea leaves grown at high altitudes were prone to possess a richer aroma, and their tea infusions also had better quality [34]. ...
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The volatile compounds of three world-famous black teas (Darjeeling, DJL, Keemun, KM, and Ceylon, CL) were extracted by stir bar sorptive extraction (SBSE), and analyzed by gas chromatography–olfactometry (GC–O), gas chromatography–mass spectrometry (GC–MS). The results indicated that 78, 76, and 69 volatile compounds were detected in the three tea infusions. And 9 sulfur compounds in black teas were identified by gas chromatography–flame photometric detection (GC–FPD). In addition, a total of 42 aroma compounds were perceived and 38 compounds were identified as important aroma compounds due to their high odor activity values (OAVs), such as 3-methylbutanal (OAV: 24–82), linalool (OAV: 24–64), geraniol (OAV: 2–97), β-ionone (OAV: 54–122), and cis-jasmone (OAV: 2–119). According to the results of aroma recombination and omission experiments, 2-methylbutanal, linalool, methyl salicylate and β-cyclocitral were confirmed to be the key aroma compounds in Darjeeling black tea, 3-methylbutanal, hexanal, β-myrcene, and methyl salicylate were the key aroma compounds in Keemun, while β-ionone, linalool, 2-methylbutanal, and salicylaldehyde were the key aroma compounds in Ceylon black tea.
... In addition, the aroma of tea beverages is also a key factor in attracting consumers. Although volatiles only account for a notably small fraction, they play an extremely important role in the sensory attributes and quality formation of tea beverages [4]. ...
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Hydrogen peroxide has a significant effect on the flavor of tea beverages. In this study, the yield of hydrogen peroxide in (–)-epigallocatechin gallate (EGCG) solution was first investigated and found to be significantly enhanced under specific conditions, and the above phenomenon was amplified by the addition of linalool. Then, an aqueous hydrogen peroxide solution was added to a linalool solution and it was found that the concentration of linalool was significantly reduced in the above-reconstituted system. These findings were verified by extending the study system to the whole green tea infusions. The results suggested that the production of hydrogen peroxide in tea beverages may be dominated by catechins, with multiple factors acting synergistically, thereby leading to aroma deterioration and affecting the quality of tea beverages. The above results provided a feasible explanation for the deterioration of flavor quality of green tea beverages with shelf life.
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Fatty acids (FAs) are important precursors of oolong tea volatile substances, and their famous derivatives have been shown to be the key aroma components. However, the relationship between fatty acids and their derivatives during oolong tea production remains unclear. In this study, fresh Tieguanyin leaves were manufactured into oolong tea and green tea (control), and fatty acids and fatty acid-derived volatiles (FADV) were extracted from processed samples by the sulfuric acid–methanol method and solvent-assisted flavor evaporation (SAFE), respectively. The results showed that unsaturated fatty acids were more abundant than saturated fatty acids in fresh leaves and decreased significantly during tea making. Relative to that in green tea, fatty acids showed larger variations in oolong tea, especially at the green-making stage. Unlike fatty acids, the FADV content first increased and then decreased. During oolong tea manufacture, FADV contents were significantly and negatively correlated with total fatty acids; during the green-making stage, methyl jasmonate (MeJA) content was significantly and negatively correlated with abundant fatty acids except steric acid. Our data suggest that the aroma quality of oolong tea can be improved by manipulating fatty acid transformation.
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This study reports the utilization of two-step headspace (HS) to profile the volatile compounds of flue-cured tobacco. The relationship between the volatile components and geographic origin was investigated using multivariate data analysis. To avoid the impact of adsorption caused by tobacco on the HS extraction, the tobacco was soaked by saturated NaCl solutions prior to the HS sampling. However, the introduction of water vapor may affect the subsequent gas chromatography–mass spectrometry (GC–MS) analysis. Thus, two-step HS, which is based on the coupling of the programmed temperature vaporizer inlet and HS autosampler, was employed to remove the water vapor while simultaneously preconcentrating the volatile compounds. The repeatability and stability were evaluated, and 80 compounds were identified from 25 flue-cured tobacco samples. Both principal component analysis (PCA) and hierarchical clustering analysis (HCA) revealed that the volatile components of flue-cured tobacco were closely related to the geographic origin. Furthermore, the characteristic volatiles of the flue-cured tobacco from different regions were illustrated using partial least squares discriminant analysis (PLS-DA). The presented work provided a simple and reliable way to profile the volatile components and characterize geographic origin of tobacco and tobacco products.
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The present study aimed to systematically investigate black tea aroma formation during the fermentation period. In total, 158 volatile compounds were identified. Of these, most amino acid-derived volatiles (AADVs) and carotenoid-derived volatiles (CDVs) showed significant increases, while fatty acid-derived volatiles (FADVs) and volatile terpenoids (VTs) displayed diverse changes during the fermentation period. During this time, fatty acids, amino acids, carotenoids, and glycosidically bound volatiles (GBVs, especially primeverosides) were found to degrade to form aroma components. Further, equivalent quantification of aroma showed that the intensity of green scent was notably decreased, while the intensities of sweet and floral/fruity scents were greatly increased and gradually dominated the aroma of tea leaves. AADVs and CDVs were shown to make greater contributions to the formation of sweet and floral/fruity scents than VTs. Our study provides a detailed characterization of the formation of sweet and floral/fruity aromas in black tea during the fermentation period.
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Rationale: In recent years, white tea has become increasingly popular. Some merchants confuse the age of white tea and sell poor-quality products for profit. Therefore, it is necessary to provide technical support for product authentication and valorization in white tea of different marked ages. Methods: Volatile organic compounds (VOCs) were detected by proton transfer reaction time of flight-mass spectrometry (PTR-TOF-MS) and identified as volatile fingerprints. PTR-TOF-MS combined with multivariate analysis was found to identify white tea of four different marked ages (1, 3, 5, and 8 years) for authentication. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were used as classification models to identify key volatile metabolites. Results: The OPLS-DA model achieved the best result (96.67%, 96.67%,96.67%, and 96.67% in the training set and 96.00%,96.00%, 100% and 100% in the prediction set for 1-year, 3-year, 5-year and 8-year tea samples, respectively), showing that PTR-TOF-MS with the OPLS-DA model could successfully be used in the identification of white tea with different marked ages. Out of the 60 identified volatile organic compounds, 26 volatile materials were closely correlated with tea age and were used as markers to discriminate white tea of different ages. Conclusions: PTR-TOF-MS coupled with multivariate analysis could be applied for quality evaluation of tea products of different ages and provided a feasible technical support for product authentication and valorization in white tea of different marked ages.
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This study aims to investigate the influence of different harvesting seasons on the aroma of black tea and the trend in the tea aroma variation. A total of 68 volatile substances was identified by gas chromatography coupled with ion-mobility spectrometry (GC-IMS), and 20 characteristic aroma-active compounds were quantitatively analyzed by gas chromatography-olfactometry coupled with aroma extract dilution analysis (GC-O AEDA) and odor activity value (OAV) analysis. These aroma-active compounds are mainly linalool, β-damascenone, and benzeneacetaldehyde. Both methods confirmed that the aroma of tea changes with the harvesting seasons, showing a downward trend followed by an upward trend. Besides, black teas harvested in different seasons have their characteristic volatile compounds and metabolism precursors. The degradation of glycosides, carotenes, and amino acids are the most important degradation pathways for the formation of tea aroma. The PLSR results of GC-O-AEDA, OAV, and DSA data agree with each other, showing that five aroma attributes of the autumn tea have strong correlations. The autumn tea has the richest aroma, followed by the spring tea and the summer tea.
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Red-light withering (RLW) was shown to improve the aroma of summer-autumn black tea, probably due to the increase in the content of main floral aroma components. Analysis of the dynamic changes of volatile components during withering showed that RLW mainly played a role in the late withering period. Non-target metabolomics and transcriptomics were used to analyze the main biosynthetic pathways of volatile components. RLW was shown to significantly up-regulate the expression of terpene synthesis-related genes (LIS, FAS, etc.) in the late withering stage and further promote the synthesis of volatile terpenoids (linalool and α-farnesene). Meanwhile, RLW leaves could release more leaf alcohol in the late withering period, due to the high expression of enzyme genes (LOX, ADH). Additionally, RLW could significantly increase the content of phenylethyl alcohol in the early withering stage. Moreover, the relative content of volatile bound glycosides (GBVs) did not change significantly among the three treatments (0 h, RLW9h and CK9h) after withering, suggesting that the hydrolysis of GBVs contributed little to aroma content during withering. Overall, RLW can significantly increase the activity of glycosidase in the later withering stage, thus improving the aroma quality of black tea in the subsequent processing.
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Fatty acid derived volatiles (FADVs) are major contributors to the aroma quality of oolong tea ( Camellia sinensis ). Most of the processing time for oolong tea is taken up by turning over treatments, but the full profile of fatty acid metabolic changes during this process remains unclear. In this study, we detected fatty acids, their derived volatiles, and related genes of Tieguanyin oolong tea using biochemical and molecular biology methods. The results showed that with an increase in turning over intensities, the content of total unsaturated fatty acids continuously dropped and the content of characteristic FADVs, such as hexanoic acid (Z)-3-Hexenly ester and 2-exenal, continued to increase. Lipoxygenase (LOX), a key gene family in the fatty acid metabolic pathway, showed different patterns, and CsLOX1 (TEA025499.1) was considered to be a key gene during the turning over processes. We found that fruit-like aroma (Z)-3-Hexen-1-ol acetate had a strong correlation with the expression levels of eight Camelia sinensis LOX family genes. Tieguanyin had relatively rich pleasant volatile compounds with moderate turning over intensity (five times turning over treatments). This study provides an overall view of how fatty acid metabolites change and affect the quality of oolong tea with different turning over intensities during processing.
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Chinese people have consistentlypreferred high mountain tea because specific flavors are memorable for them, and also, people have traditionally considered this type of tea to be good for health. Tieguanyin is one of the famous traditional Chinese tea that has ever-changing aromas. To illustrate the various characteristics in volatile fragment compounds from Tieguanyin tea, fresh tea leaves collected from different elevations (450, 650, and 900 m) were detected using GC-MS by solid–liquid extraction. The results showed that volatile aromatic compounds, such as benzyl alcohol, phenyl ethanol, and acetophenone, were the most abundant in tea leaves located with high elevation. Meanwhile, 1-hexanol, 1-nananol, and nanoic acid, as a type of aliphatic aroma, were more prevalent in low-elevation tea orchards. Catechols and alkaloids are largely cumulated in low- and high-elevation tea leaves, respectively. Our findings also showed that elemene was widely consisted of high-elevation tea metabolites. It provided practicality for the preparation of tea manufacturing in major Tieguanyin tea-producing regions.
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The aroma profile of sun-dried black tea (SBT) was identified by headspace solid–phase microextraction (HS–SPME) coupled with gas chromatography–mass spectrometry (GC–MS) and gas chromatography–olfactometry (GC–O). A total of 37 scents were captured by using the GC–O technique, and 35 scents with odor intensities ranging from 1.09 ± 1.93 to 9.91 ± 0.29 were identified. Twenty-one compounds were further identified as key odor-active compounds with odor activity values (OAVs) greater than or equal to one. These key odor-active compounds were restructured with their detected concentrations, and the aroma profile of the selected SBT sample was successfully imitated to a certain extent. An omission test was performed by designing 25 models and confirmed that (E)-β-damascenone, β-ionone, dihydro-β-ionone, linalool, and geraniol were the key odor-active compounds for the aroma profile of SBT. Meanwhile, phenylethyl alcohol, (E)-2-decenal, hexanal, and methyl salicylate were also important to the aroma profile of SBT. This study can provide theoretical support for the improvement of the aroma quality of sun-dried black tea.
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Changes in key odorants and aroma profiles of Qingzhuan tea (QZT) during its manufacture were determined using headspace solid-phase microextraction gas chromatography-mass spectrometry/olfactometry. An aroma profile was constructed to illustrate sensory changes during manufacture. The characteristic aroma of QZT was aged fragrance, which was mostly developed during pile fermentation and was enhanced during the aging and drying stages. Using volatile compounds found in the raw materials, sun-dried green tea and QZT finished product were compared by orthogonal partial least square-discriminant analysis. Among 108 detected volatiles, 19 were significantly upregulated and 15 were downregulated. (E)-β-Ionone, (E,Z)-2,6-nonadienal, 1-octen-3-one, (E,E)-2,4-heptadienal, (E,E)-2,4-nonadienal, safranal, (E)-2-nonenal, α-ionone, and 1,2,3-trimethoxybenzene were found to be significant contributors to the aged QZT fragrance, reflecting their high odor-activity values and aroma intensities. Finally, the metabolic transformation of key aroma-active compounds was systematically analyzed. This study provided a theoretical basis for improving the processing and quality of QZT.
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Tea cultivar is crucial for oolong tea aroma quality. However, the aroma characteristics of oolong tea made from different cultivars have rarely been studied. The aroma profiles of fresh tea leaves and oolong teas derived from Shuixian (SX), Huangmeigui (HMG) and Zimudan (ZMD) cultivars were comprehensively analyzed by gas chromatography-mass spectrometry, gas chromatography-ion mobility spectrometry (GC-IMS), sensory evaluation and odor activity value (OAV) determination. 12 volatiles (OAV>1) contributed to the overall aroma, of which benzeneacetaldehyde (OAV 2.14) and 3,5-diethyl-2-methylpyrazine (OAV 1.25) were the aroma-active compounds for HMG tea. Significantly more volatiles and stronger floral odor were from HMG and ZMD than the SX tea. Moreover, popcorn-like, creamy odors with high-intensity, and caramel-like odor were only recorded in HMG and ZMD samples. Additionally, 27 volatiles were identified by GC-IMS only, indicating the benefits of combined method for a better understanding of the impact of cultivars on tea aroma profiles.
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Dancong is a Chinese oolong tea famous for its aroma diversity. However, this diversity in characteristic is challenging to be clarified in either sensory or chemical aspects. In this study, the aromas from Dancong teas were characterized based on the typical odors of “floral” and “honey”. The volatile compounds underlying the odors were investigated through chemometrics. Seventy Dancong teas of various categories were collected to approximate the diversity in aroma. According to the sensory evaluation, the floral or honey odor was detected at every sample. For volatile characterization, 57 compounds were identified by gas chromatography-mass spectrometry (GC-MS) coupled with headspace-solid phase microextraction (HS-SPME) across samples. The difference in floral and honey odors was related to volatile variation among the teas, as both the odor-based classification and the volatile-based unsupervised learning analyses yielded consistent sample clustering patterns. Nine volatiles were identified as putative markers for the odor difference, where indole, (E)-nerolidol, 2-phenylacetonitrile and γ-caprolactone were accounted for the floral odor predominance, while hexyl 2-methylbutanoate, (Z)-3-hexenyl pentanoate, (Z)-linalool oxide (pyranoid), (E)-linalool oxide (furanoid), and (Z)-linalool oxide (furanoid) were contributed to the honey odor perception. These results point to a volatile-endorsed categorization framework based on the floral and honey odors that can assist Dancong aroma quality control.
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Flavour is a crucial sensory element that determines the consumers’ preference for food and beverages. In this study, we determined the effects of complex gum arabic (GA) and tannic acid (TA) on the aroma release of flavour oil emulsions in vitro by simulating oral processing conditions. GA and TA were used to stabilize flavour oil emulsions. Visualization of in vitro retention using ex vivo porcine tongue, detection of aroma release in the model mouth, and sensory evaluation of flavour emulsions were performed to determine the effect of TA and GA. The results indicated that the retention of emulsions and the release of aroma compounds were modulated by TA and GA, which could be because of interactions that occurred between GA and TA in emulsions and mucins on the tongue. GA enhanced aroma release, whereas TA contributed to the retention or slow release of target aroma compounds.
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Maize sprouts are currently studied as one of novel nutritional sprout foods with special flavor. This study focused on the influences of light qualities on volatiles accumulation in maize sprouts by integrating transcriptomic and metabolic works. Fatty acid derivatives, including nonadecane and n-hexadecanoic acid were highly existed in maize sprouts. Besides, aldehydes and apocarotenoids were accumulated in light qualities whereas unsaturated fatty acids and sesquiterpenoids were declined by light qualities. The enhancements on fatty acid and phenylpropanoids/benzenoids derivatives of blue light quality were stronger than that of red light quality. In addition, there were nuances between blue and white light qualities, hence blue light quality was supposed to be an alternative energy-saving choice for cultivating maize sprouts. A MYB transcription factor was upregulated in light qualities and might play negative roles on linolenic acid degradation. C2H2 probably involved in the discrepant accumulation of terpenoids in maize sprouts treated by blue and red light qualities. The specific MYBs and bHLHs were correlated with terpenoid biosynthesis while a PL1 gene served as a potential regulator on phenylalanine biosynthesis flux. These findings provided new tactics for volatiles accumulation in maize sprouts as well as new insight into the volatile regulatory mechanism.
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Taiping Houkui green tea is well-known in China for its noble aroma. Six tea strains from the Shidacha population (the predominant raw materials for Taiping Houkui green tea) and three other varieties were used to prepare green teas via the conventional techniques of Taiping Houkui green tea manufacture. Aroma evaluation confirmed that green teas produced from Shidacha strains possessed good aroma qualities. A total of ninety-six volatile compounds were identified and quantified. Hierarchical cluster analysis separated the nine green teas into three groups, and principal component analysis identified 16 volatiles (with variance importance values greater than one) that contributed to the separation. Thirty-three volatiles with odor activity values above one were identified, the highest twenty being methyl epi-jasmonate, octanal, (Z)-jasmone, β-ionone, geraniol, indole, methyl jasmonate, nonanal, decanal, linalool, benzeneacetaldehyde, phenylethyl alcohol, α-ionone, 1-octen-3-ol, cedrol, benzaldehyde, dimethyl sulfide, hexanal, 3-methylbutanal, and β-cyclocitral. All of these may be key odorants in Taiping Houkui green tea. This study suggests that the unique aroma of Taiping Houkui green tea depends both on a premium tea plant and the manufacturing process.
Article
Jinmudan (JMD) black tea is processed from the JMD cultivar (Camellia sinensis (L.) O. Kuntze cv. Jinmudan). Dried JMD black tea (JMD-D) received a score of 7.43 in the quantitative descriptive analysis, indicating that it had the strongest fruity flavor. Many volatile compounds (129) were identified by solvent assisted flavor evaporation and gas chromatograph mass spectrometry. In total, 26 aroma active compounds, including (Z)-methyl epi-jasmonate (flavour dilution factor (FD): 128–1024), benzeneacetaldehyde (FD: 512–1024), linalool (FD: 256–1024), geraniol (FD: 256–512), jasmine lactone (FD: 256–512), were identified in JMD-D and controls through an aroma extract dilution analysis and gas chromatography-mass spectrometry olfactometry. On the basis of the FD values, odor activity values, and relative quantification results, the volatiles of fruit flavor derived from lipids, such as jasmine lactone, were prominent in JMD-D compared to the control. During the processing of the four types of black tea, the volatile fraction concentration increased mainly from the fresh leaf to the fermentation stage and decreased in the drying stage.
Article
To explore the impact of harvest season in white tea, high-performance liquid chromatography (HPLC) and amino acid analyzer were developed for the determinations of 17 phenolic compounds, 3 purine alkaloids, 19 amino acids, γ-aminobutyric acid (GABA) and 4 main quality components in 18 Bai mudan sub-type of Xinyang white teas harvested in spring, summer and autumn seasons, respectively. Additionally, the in vitro antioxidant capacity was evaluated by 5 various assays. Principal component analysis (PCA), hierarchical cluster analysis (HCA) and partial least squares-discriminant analysis (PLS-DA) could completely classify these white teas by the harvest season, and indicated its profound impact on chemical composition in white tea. 14 Characteristic compounds (VIP ≥1.0), such as (−)-epigallocatechin (EGC), gallic acid, caffeine, l-theanine, conduced to identify the harvest season of white tea. Through comparison, the spring tea was observed to possess the highest amino acids, catechins contents and in vitro antioxidant capacity. (−)-Epicatechin (EC), EGC, (−)-epicatechin gallate (ECG) and (−)-epigallocatechin gallate (EGCG) were considered as the major antioxidants in white tea due to their highly significantly (p < 0.01) positive correlations. Overall, the research results provided support for the identification of harvest season in white tea.
Article
Tea is one of the biggest categories of modern non‐alcoholic beverages with health benefits. Through different processes, tea products are divided into six main types: green tea, yellow tea, white tea, oolong tea, black tea, and dark tea. Metabolomics is helpful for the comprehensive, accurate, and rapid determination of tea metabolites in different types of tea products and tea processing materials. It has been widely applied in studying the relationship of tea metabolites and its quality. Therefore, it is necessary to summarize the application of metabolomics in tea. In this review, we described and summarized 1) the main metabolites of six types of tea and their implications on tea quality with emphasis on the content differences of the main metabolites in different types of tea; 2) the research on optimizing the key processing steps of six types of tea based on metabolomics and the discussion of various new strategies for effectively improving their quality; and 3) the advanced approach to characterize and distinguish different grades of tea products via metabolomics. The current review offers guidance for the improvement of tea quality by metabolomics and its potential challenges.
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Article
Processing is the crucial factor for green tea aroma quality. In this study, the aroma dynamic changes throughout the manufacturing process of chestnut-like aroma green tea were investigated with gas chromatography electronic nose (GC-E-Nose), gas chromatography-ion mobility spectrometry (GC-IMS), and comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS). GC-IMS identified 33 volatile compounds while GC×GC-TOFMS identified 211 volatile components. Drying exerted the greatest influence on the volatile components of chestnut-like aroma green tea, and promoted the generation of heterocyclic compounds and sulfur compounds which were commonly generated via the Maillard reaction during the roasting stage. A large number of heterocyclic compounds such as 1-methyl-1H-pyrrole, pyrrole, methylpyrazine, furfural, 2-ethyl-5-methylpyrazine, 1-ethyl-1H-pyrrole-2-carboxaldehyde, and 3-acetylpyrrole were newly formed during the drying process. This study also validated the suitability of GC-E-Nose combined with GC-IMS and GC×GC-TOFMS for tracking the changes in volatile components of green tea throughout the manufacturing process.
Article
Drying is an important factor in the formation of green tea flavor. In this study, metabolomic analysis were used to detect characteristic components of four green teas with clean aroma (CA), chestnut-like aroma (CLA), bean-like aroma (BLA) and high-fired aroma (HFA) produced by adjusting drying temperature. The sensory evaluation results showed that the tea dried at 90 °C,110 °C, 160 °C and 180 °C had a clean aroma, chestnut-like aroma, bean-like aroma and high-fired aroma respectively. A total of 95 volatile compounds were identified. Linalool, naphthalene, 2-methyl-naphthalene, 1-octen-3-ol contributed most to the clean aroma. 1,2-dihydro-1,1,6-trimethyl-naphthalene was the key component of the chestnut-like aroma. 2,3-diethyl-5-methyl-pyrazine, 2-methyl-butanal, 3-ethyl-2,5-dimethyl-pyrazine had the biggest contribution to the bean-like aroma. 2,3-diethyl-5-methyl-pyrazine, 3-ethyl-2,5-dimethyl-pyrazine and 2-ethyl-5-methyl-pyrazine contributed most to the high-fired aroma. A total of 838 non-volatile compounds were detected and amino acids, saccharides decreased while catechins, flavonols increased during the increasing of drying temperature. It's found that they were related to the taste of umami, astringency and bitterness. This result provides a guidance and theoretical basis for the processing of green tea with different aroma types.
Article
Suitable picking tenderness is an essential prerequisite for manufacturing tea. However, the influence of picking tenderness of fresh tea leaves on the aromatic components is still unclear. In this study, aromatic profiles and chiral odorants in fresh tea leaves and corresponding baked green teas with five levels of tenderness of two representative cultivars were analysed using stir bar sorptive extraction-gas chromatography-mass spectrometry. cis-Linalool oxide (furanoid) and methyl salicylate exhibited significantly increasing trends as samples of all series matured. The content of most chiral odorants was significantly high in the mature samples, and significant content variations of all enantiomers during baked green tea processing could be observed with different trends according to their precursors. In particular, the enantiomeric ratios of most chiral odorants were less influenced by the picking tenderness and processing, while drying (limonene), spreading and fixation (α-terpineol), and spreading (dihydroactinidiolide) influenced the chiral distribution of the aforementioned odorants.
Article
Two major green leaf volatiles (GLVs) in tea that contribute greatly to tea aroma, particularly the green odor, are (E)-2-hexenal and (Z)-3-hexenal. Until now, their formation and related mechanisms during tea manufacture have remained unclear. Our data showed that the contents of (E)-2-hexenal and (Z)-3-hexenal increased more than 1000-fold after live tea leaves were torn. Subsequently, a new (Z)-3:(E)-2-hexenal isomerase (CsHI) was identified in Camellia sinensis. CsHI irreversibly catalyzed the conversion of (Z)-3-hexenal to (E)-2-hexenal. Abiotic stresses including low temperature, dehydration, and mechanical wounding, did not influence the (E)-2-hexenal content in intact tea leaves during withering, but regulated the proportions of (Z)-3-hexenal and (E)-2-hexenal in torn leaves by modulating CsHI at the transcript level. For the first time, this work reveals the formation of (E)-2-hexenal during tea processing and suggests that CsHI may play a pivotal role in tea flavor development as well as in plant defense against abiotic stresses.
Article
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Volatile organic compounds (volatiles) comprise a chemically diverse class of low molecular weight organic compounds having an appreciable vapor pressure under ambient conditions. Volatiles produced by plants attract pollinators and seed dispersers, and provide defense against pests and pathogens. For insects, volatiles may act as pheromones directing social behavior or as cues for finding hosts or prey. For humans, volatiles are important as flavorants and as possible disease biomarkers. The marine environment is also a major source of halogenated and sulfur-containing volatiles which participate in the global cycling of these elements. While volatile analysis commonly measures a rather restricted set of analytes, the diverse and extreme physical properties of volatiles provide unique analytical challenges. Volatiles constitute only a small proportion of the total number of metabolites produced by living organisms, however, because of their roles as signaling molecules (semiochemicals) both within and between organisms, accurately measuring and determining the roles of these compounds is crucial to an integrated understanding of living systems. This review summarizes recent developments in volatile research from a metabolomics perspective with a focus on the role of recent technical innovation in developing new areas of volatile research and expanding the range of ecological interactions which may be mediated by volatile organic metabolites.
Article
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Tea (Camellia sinensis) is one of a few plants accumulating aluminium (Al), making tea a major source of dietary Al intake. This paper reviews published studies on the concentrations, speciation and bioavailability of Al in tea. With very few exceptions, the total concentration of Al in tea infusions is in the range 1–6 mg l−1. Probably more than 90% of this Al is bound to organic matter, but the nature of the organic species is unclear. Three studies using size exclusion chromatography provide evidence for Al species in the molecular mass (MM) range 4000–8500 Da, probably polyphenolic complexes. Two ultrafiltration studies indicate the presence of Al species with MMs above 10,000. The relative amount of the different organic Al species in tea infusions is unclear, and even the identity of any of these has not been demonstrated with certainty. A possible exception is Al trioxalate, which may be an important species based on evidence from two 27Al-NMR studies. It seems fairly well established that drinking tea leads to measurable, but moderate increases in urinary Al excretion. However, the Al present in tea does not seem to be much more bioavailable than that from other dietary sources. Even so, it cannot be dismissed that tea infusions may contain particularly bioavailable and neurotoxic compounds such as Al maltolate, but this is at present speculative.
Article
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Darjeeling teas are the highest grown teas in the world and preferred for its flavour, aroma and quality. Apart from the genetic makeup of the plant, earlier reports suggest that insect infestation, particularly jassids and thrips triggers the aroma and flavour formation in Darjeeling tea. The present work encompasses the identification of the genes/transcriptomes responsible for the typical flavour of Darjeeling tea, besides understanding the role of jassids and thrips in particular, in producing the best cup character and quality. The quantitative real time PCR analysis was based on a suppression subtractive hybridisation forward library of B157 (tea clone infested with thrips), providing us transcripts related to aroma and flavour formation. We observed the expression of genes like leucine zipper, ntd, nced, geraniol synthase, raffinose synthase, trehalose synthase, amylase, farnesyl transferase, catalase, methyl transferase, linalool synthase, peroxidases, elicitor responsive proteins, linamarase, nerolidol linalool synthase 2, 12-oxophytodienoate reductase, glucosidase, MYB transcription factor, and alcohol dehydrogenase, highly regulated due to insect infestation, manufacturing stresses and mechanical injury. The first report on gene expression dynamics in thrips infested Darjeeling tea leaves can be extrapolated with increase in volatiles which is responsible for enhancing the quality of Darjeeling tea, specially the flavour and aroma of the infusion. We hope to model these responses in order to understand the molecular changes that occur during Darjeeling tea flavour formation.
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Seasonal and clonal variations in glycosidic bound volatile compounds were studied in tea clones representing the three different varieties viz. sinensis, assamica and cambodiensis grown in Kangra region. Glycosidic bound volatile compounds were characterised by GC-MS and quantification of major volatiles was done by GC. (E)-2-hexenal, benzyl alcohol, phenylethanol, linalool, linalool oxides, geraniol and methyl salicylate were the major glycosidic bound volatiles identified in tea shoot. Clonal variations in the quantity were observed in these bound volatiles. Seasonal variations were also observed in the quantity of bound volatiles in regional Kangra clone during three different growth flushes of tea. These variations in glycosidic precursors of volatile compounds were studied in context with orthodox made tea and its quality. These seasonal and clonal variations in precursors of volatile compounds can be directly correlated to the difference in the quality of tea made from these cultivars.
Article
Methyl epijasmonate has a 400 times stronger aroma than methyl jasmonate, which is known to be one of the key compounds in the aroma of tea, and the former is easily isomerized on heating. Reinvestigation of the separation and identification of tea aroma compounds indicated that steam distillation should be performed under reduced pressure, and that the gas chromatographic conditions should be controlled at below 170°C using an open tubular column coated with a non-polar liquid phase to avoid the isomerization or decomposition of methyl epijasmonate. Under the conditions, ten types of teas were analyzed, and methyl epijasmonate was shown to contribute to the aroma of tea, particularly, to that of Chinese semi-fermented teas. © 1988, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.
Article
Reliability is an important design index. Variable wind speed is one of the important factors causing trajectory scatter. For the large and complex system, it is too difficult to analyze the reliability using the analytic methods, but the computer simulation is an effective way. Reliability simulation for flight control system is studied in detail by considering variable wind speed. The model of wind is established and randomized. Influence principle of wind for flight control system is studied, and motion equations of missile are modified. Algorithm of reliability simulation is discussed in detail, and formulae of computing reliability are given. Finally, the method is verified by X-missile's flight control system.
Article
Engineering ceramics has good property of wear resistance. In this paper, the application of toughening ZrO2 ceramics for wear part in G-M refrigerator is presented. In order to increase life span and reliability of refrigerator, ZrO2 ceramics has been applied to fabricate rotary unit, which is a wear part of G-M refrigerator. We also have studied the wear particles formed in Teflon-metal sliding and ZrO2-ZrO2 sliding respectively. The thickness of wear particles is estimated from analyses based on a model. The results show ZrO2 ceramics has the highest application potential for wear part in G-M refrigerator.
Article
The enzyme system producing cis-3-hexenal, a precursor of cis-3-hexenol (leaf alcohol) and trans-2-hexenal (leaf aldehyde), from linolenic acid showed high activity in summer and no activity in winter in tea (Thea sinensis) leaves and isolated chloroplasts. The enzyme system producing n-hexanal from linoleic acid also showed similar seasonal changes in activity. These changes were closely related to temperature and solar radiation. Enzyme activity could not be induced after the leaves had been cut and was not accompanied by de novo protein synthesis.
Article
When tea leaves were homogenized and incubated, the volatile C6-compounds hexanal, cis-3-hexenal, cis-3-hexenol and trans-2-hexenal were formed much more by summer leaves than by winter leaves of tea plants (Camellia sinensis). The enzymes lipolytic acyl hydrolase (LAH), lipoxygenase, fatty acid hydroperoxide lyase (HPO lyase) and alcohol dehydrogenase (ADH) and an isomerization factor were responsible for the sequential reactions of C6-compound formation from linoleic and linolenic acids in tea leaf lipids, and there were seasonal changes in their activities. The tea leaf enzymes were of 3 types: LAH and lipoxygenase, which had high activities in summer leaves and low activities in winter leaves; ADH, which had low activity in summer leaves and high activity in winter ones; and HPO lyase and the isomerization factor, which did not seem to have any effect on the rate of C6-compound formation throughout the year. Changes in enzyme activities were induced by shifts in the environmental air temperature rather than by the age of the leaves. The combined activities of these enzymes determined the amounts and compositions of the volatile C6-compounds formed, which are the factors that control the quality of the raw leaves processed for green tea.
Article
The effects of the tea manufacturing process (heat-drying, pan-firing, solar-drying and fermentation) on the production of carotenoid-derived aroma compounds are discussed. Several carotenoid-derived aroma compounds are important in the development of fine tea flavor. In the present study, we analyzed the volatile components of tea infusions using a brewed extraction method and gas chromatography/mass spectrometry (GC/MS). An analysis of aroma patterns showed that the concentrates prepared by the brewed extraction method are quite different from those obtained by the steam distillation/extraction (SDE) method. Extracts of black tea that were prepared using the brewed extraction method contained only dihydroactinidiolide and theaspirone as carotenoid-derived aroma compounds. The photo-oxidation effect of solar-drying was also examined using a model experiment.
Chapter
The custom of drinking tea has spread all over the world. Camellia sinensis tea is the most popular beverage in the world, and mate tea (Ilex paraguaryensis) and rooibos tea (Aspalathus linearis) are locally consumed in South America and South Africa (Dahlgren 1968), respectively. The aroma is the major factor contributing to tea quality and enjoyment. Research into characterizing tea aroma has been carried out for past 100 years, and more than 600 volatile compounds have been reported or isolated by using GC or GC-MS, in spite of the small quantity of essential oil (600 ppm) (Straten and Maarse 1989; Yamanishi 1995). Although more than 99.9% of tea essential oil has been determined, characterizing tea aroma has remained unidentified. The problem has been caused by the severe preparation process for aroma concentrates. Tea aroma varies with current extraction methods such as SDE (simultaneous distillation and distraction) or SDR (steam distillation under reducing pressure), and the aroma concentrate obtained through these preparation processes no longer has the original tea aroma.
Article
Alcohol dehydrogenase (alcohol: NAD oxidoreductase, E. C. 1. 1. 1. 1.) from Thea sinensis seeds (variety: Zairai) was isolated and purified about 1, 500-fold using preparative disc electrophoresis. The specific activity was about 3.4units/mg protein against ethyl alcohol. Its s020. w value was 6.96S and its molecular weight was approximately 150, 000 using gel filtration on Sephadex G-200. The physical, chemical and catalytic properties of the enzyme are described. The oxidoreduction products formed by the enzyme were identified by gas chromatography, and for the unsaturated compounds the conversion of double bond and geometrical isomerization was observed. The substrate specificity of tea enzyme is discussed in comparison with the enzymes from Leuconostoc mesenteroides, and horse and human livers. Paticularly a tendency for reactivity in the oxidoreduction of unsaturated alcohols and aldehydes were discribed by comparing the effects of geometry, the position of the double bond and the length of chain in substrates.
Article
The seasonal variations in the amounts of C6-volatile components cis-3-hexenal trans-2-hexenal n-hexanal) and their precursors (linoleic and linolenic acid) in homogenates of Thea sinensis leaves were quantitatively analyzed throughout the year. Formation of trans-2-hexenal began in the middle of April and reached a maximum during July. Towards autumn the aldehyde gradually decreased and, in winter (December to March), was virtually absent. The levels of cis-3-hexenol remained constant during May–December. cis-3-Hexenal showed a similar variation pattern to that of trans-2-hexenal. The major fatty acids in the leaves were palmitic, palmitoleic, oleic, linoleic and linolenic acid, and occurred in non-ionic lipids and phospholipid fractions. The amounts of linoleic and linolenic acid did not show any marked variation except for a big peak in October.
Article
Hydroperoxide cleaving enzyme, hydroperoxide lyase (HPO lyase), was firstly purified to homogeneity from membranous fraction of tea leaves. The enzyme was separated with hydroxyl apatite gel chromatography into two fractions, HPO lyase I and II having Mr of 55 000 and 53 000, respectively. Almost the same pH-activity profiles were obtained with these two forms of HPO lyases. Antioxidants which are known as potent inhibitors for lipoxygenase such as nor-dihydroguaiaretic acid and butylated hydroxyanisole inhibited the activity of HPO lyase I. Activity for 13-hydroperoxide of α-linolenic acid was ca 10 times higher than that for 13-hydroperoxide of linoleic acid but the positional isomer, 13-hydroperoxide of γ-linolenic acid was a relatively poor substrate.
Article
The biosynthetic pathway of trans-2-hexenal, leaf aldehyde, in isolated chloroplasts of Thea sinensis leaves. was examined using a tracer experiment. A high and specific incorporation of radioactivity into cis-3-hexenal and trans-2-hexenal, was observed when linolenic acid-[U-14C] was incubated with the isolated chloroplasts. Thus, trans-2-hexenal was biosynthesized via cis-3-hexenal from linolenic acid in the chloroplasts.
Article
Leaves of the Japanese Camellia sinensis cultivar “Yabukita” were used for the elucidation of structural patterns of carotenoid cleavage enzymes. The enzymes were isolated from fresh tea leaves in active form and purified to single band in SDS PAGE gels. Subsequently, the specific activity of the carotenoid cleavage enzymes was tested and the positive fractions selected for further analysis. The phosphate content of the purified enzyme was elucidated by three different methods: phosphatase assays, fluorescence marker kits and by measuring ammoniumheptamolybdate complexes after incineration of the samples. In all cases phosphorylations of the respective samples could be detected, thus giving evidence for an overall increase of the phosphorylations level of proteins in C. sinensis from spring (1.84μg/mg) to autumn (2.39μg/mg). Consequently, carotenoid cleavage enzymes isolated in autumn also showed higher phosphorylation levels, which may as well correspond to changes on the functional level between spring (Michaelis Constant (Km)=9.45μmol/L) and autumn (Km=17.16μmol/L).
Article
The contributors to the differences in the odors of different grades of green tea were selected, and the relations to the odors of their infusions are discussed. D-Nerolidol, 6-methyl-alpha-ionone, methyl jasmonate, coumaran, indole, and coumarin were possible contributors to a typical green tea odor. 3-Hexenoic acid and methyl jasmonate along with aliphatic alcohols and aldehydes provided fresh and brisk odors. 3-Hexenoic acid, 3,5,5-trimethyl-2(5H)-furanone, and 5,6,7,7a-tetrahydro-4,4,7a-trimethyl-2(4H)-benzofuranone gave deep and mild odors. Linalool, 2,6-dimethyl-1,3,7-octatrien-6-ol, benzeneacetaldehyde, and 3-hexenyl hexanoate afforded floral and fruity odors. 1-Ethyl-1H-pyrrole-2-carboxyaldehyde, 3-ethyl-4-methyl-1H-pyrrole-2,5-dione, 3-ethyl-3-methyl-2,5-pyrrolidinedione, coumaran, and coumarin provided burnt and sweet odors. 2-Methylbenzonitrile, a,5-diethylphenol, and 2-ethyl-4,5-dimethylphenol afforded woody and green odors. D-Limonene, acetic acid, linalool, 2,6-dimethyl-1,3,7-octatrien-6-ol, benzeneacetaldehyde, and 3-hexenyl hexanoate gave harsh and sickening odors, while (E)-2-hexenal and (E,Z)-2,4-heptadienal gave green and sickening odors. 3-Hexenic acid and D-nerolidol provided a deep odor.
Article
The cyanoglycoside, prunasin, was isolated for the first time as an aroma precursor of benzaldehyde from fresh tea leaves (Camellia sinensis var, sinensis cv. Yabukita). Prunasin was readily hydrolyzed by a crude enzyme prepared from the fresh tea leaves to liberate benzaldehyde. The isomerization of prunasin under neutral conditions was also recognized.
Article
Two epimers of methyl jasmonate were optically resolved by capillary gas Chromatography, using heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin as the chiral stationary phase. In the tea volatile concentrates, both of these epimers were present as only one en-antiomer, their absolute configurations being ascertained as (-)-(1R,2R)-methyl jasmonate and (+)-(1R,2S)-methyl epijasmonate. The thermal isomerization of methyl epijamonate to methyl jasmonate was also clarified by optically resolved gas Chromatography to have occurred at the asymmetric carbon of the C-2 position that is connected to the carbonyl group.
Article
The main aroma components of oolong and black tea, linalool and four diastereomers of linalool oxides (LOs), were enantioselectively isolated by capillary gas chromatography, using a column coated with an optically active liquid phase, permethylated β-cyclodextrin.The R/S ratio varied among linalool and LOs, and among the different types of tea, the ratio for a particular compound also being different. However, the complete patterns of R/S ratio were similar in the semi-fermented and fermented teas, respectively.Using a specific cultivar of black tea, the R/S ratio for each of the five compounds was compared in the free state in black tea with that of an aglycone of the glycoside in fresh tea leaves or in black tea. While the e.e. values of the compounds varied, those for a specific compound were similar, except for linalool, regardless of their free or combined state.These results show that LOs are not directly transformed from linalool, but are formed enzymatically from glycoside precursors.
Article
Detection of tea grade by a human taste panel is affected by external factors and usually inaccurate, but it might be promising to use an electronic nose (E-nose). In this paper an investigation has been made to determine the grade of different tea samples using an E-nose. Feature vectors of the teas with different quality grade (Labeled: T120, T600, T800, T1200 and T1800) were extracted from the E-nose response signals, and the data were processed by using the principle components analysis (PCA) and linear discriminant analysis (LDA). Using the average and integrated value of feature vectors, 100% correct classification by LDA was achieved for five different tea samples with different qualities. The results indicated that the E-nose was capable of discriminating different grades of green teas.
Article
New glycosidic aroma precursors (1 and 2) of the main volatile constituents, trans- and cis-linalool 3,6-oxides (linalool oxides I and II), were isolated from oolong tea leaves (Camellia sinensis var. sinensis cv. Maoxie). The isolation was guided by an enzymatic hydrolysis with acetone powder prepared from fresh tea leaves (cv. Yabukita) followed by GC or GC-MS analyses. Chromatographic purification of hot water extracts of the tea leaves on active charcoal, Amberlite XAD-2, and Sephadex LH-20 columns as well as HPLC gave two new glycosides, trans- and cis-linalool 3,6-oxide 6-O-β-d-xylopyranosyl-β-d-glucopyra-nosides (1 and 2).
Article
We synthesized nine kinds of diglycosides and a monoglycoside of 2-phenylethanol to investigate the substrate specificity of the purified beta -primeverosidase from fresh leaves of a tea cultivar (Camellia sinensis var. sinensis cv. Yabukita) in comparison with the apparent substrate specificity of the crude enzyme extract from tea leaves. The crude enzyme extract mainly showed beta -primeverosidase activity, although monoglycosidases activity was present to some extent. The purified beta -primeverosidase showed very narrow substrate specificity with respect to the glycon moiety, and especially prominent specificity for the beta -primeverosyl (6-O-beta -D-xylopyranosyl-beta -D-glueopyranosyl) moiety. The enzymes hydrolyzed naturally occurring diglycosides such as beta -primeveroside, beta -vicianoside, beta -acuminoside, beta -gentiobioside and 6-O-alpha -L-arabinofuranosyl-beta -D-glucopyranoside, but were unable to hydrolyze synthetic unnatural diglycosides. The purified enzyme was inactive toward 2-phenylethyl beta -D-glucopyranoside. The enzyme hydrolyzed each of the diglycosides into the corresponding disaccharide and 2-phenylethanol. These results indicate the beta -primeverosidase, a diglycosidase, to be a key enzyme involved in aroma formation during the tea manufacturing process.
Article
Many volatiles in fresh tea leaf are in the forms bound with glycosides and they are released by action of ß–primeverosidase and ß-glucosidase during tea processing. Effect of ultra-violet B on release of volatiles in fresh tea leaves of two tea cultivars, “Maoxie” and “Anhui-9,” were investigated. Types of volatile and their concentration increased when ultra-violet B was applied at 3.0 μmol m−2 s−1 for 2 h and then decreased as the irradiation was extended to 6 h. The relation of expression of ß–primeverosidase and ß-glucosidase genes to the release of volatiles were also discussed.
Article
Four stereoisomers of methyl jasmonate, methyl 3-oxo-2-(2-(Z)-pentenyl)cyclopentane-1-acetate, were isolated from a commercial sample of methyl jasmonate. Enantiomeric resolution was based on the separation of (-)-bornyl jasmonate diastereoisomers with liquid chromatography. Odor detection thresholds showed that methyl (+)-epijasmonate, (1R,2B)-(+)-methyl 3-oxo-2-(2-(Z)-pentenyl)cyclopentane-1-acetate, has the strongest odor-activity.
Article
The odor concentrates from green tea prepared by a simultaneous distillation and extraction (SDE) under reduced pressure and an adsorptive column method were investigated. A total of 218 compounds were quantified and identified by GC and GC-MS. Total concentrations were 92.9 ppm by SDE and 11.9 ppm by the column method. The concentrations of aliphatic alcohols and aldehydes were 7409 and 2681 ppb in the SDE concentrate and 241 and 108 ppb in the column concentrate, respectively. The concentrations of terpene alcohols were 8399 and 807 ppb, respectively. Most of ketones were found several times in the SDE concentrate compared with the column one. Further, large quantities of 1-propen-2-yl formate, pentyl formate and (Z)-3-hexenyl butanoate were formed during SDE, while 3-hexenyl hexanoate decreased. Coumaran, coumarin, vanillin, furanones, and lactones disappeared, while aromatic aldehydes, ionone derivatives, and indole were formed in quantity during SDE operation. SDE caused serious formations and decompositions of volatile compounds in green tea infusion, but the column method gave the odor concentrate with natural green tea flavor.
Article
Volatile components of various brewed oolong teas and black teas were analyzed by gas chromatography (GC) and gas chromatography/FTIR spectrometry/mass spectrometry. The GC pattern of brewed tea extracted by dichloromethane (brewed extract) differs greatly from the GC pattern of the extract prepared by simultaneous steam distillation and extraction method (SDE). The brewed extract includes higher amounts of acids, aromatic alcohols, and monoterpenediol and lower amounts of monoterpene alcohols than the SDE extract. The Darjeeling brewed extract, which has a more complicated aroma pattern, consists of four linalool oxides, linalool, geraniol, hexanoic acid, benzyl alcohol, 2-phenylethanol, trans-geranic acid, (E)-2-hexenoic acid, (Z)-3-hexenoic acid, and 2,6-dimethyl-3,7-octadiene-2,6-diol. The Darjeeling SDE extract consists of seven main components which include geraniol, linalool, four linalool oxides, and methyl salicylate. The brewed extract of Chan Pin oolong (red oolong tea), which is similar in aroma to Darjeeling and is made from tea leaves infested with green flies (Emposca flavescens) in the same way as Darjeeling, contains very high amounts of 2,6-dimethyl-3,7-octadiene-2,6-diol. This compound appears to be the precursor of 3,7-dimethyl-1,5,7-octatrien-3-ol and to be the most important factor in Darjeeling tea flavor.
Article
Aroma is an essential factor affecting the quality of tea (Camellia sinensis) products. While changes of volatile compounds during tea manufacturing have been intensively studied, the effect of environmental factors on volatile contents of fresh tea leaves has received less attention. We found that C. sinensis var. Yabukita kept in darkness by shading treatment for 3weeks developed etiolated leaves with significantly increased levels of volatiles, especially volatile phenylpropanoids/benzenoids (VPBs). Upstream metabolites of VPBs, in particular shikimic acid, prephenic acid, and phenylpyruvic acid, showed lower levels in dark treated than in control leaves, whereas the contents of most amino acids including l-phenylalanine, a key precursor of VPBs, were significantly enhanced. In addition, analysis by ultra performance liquid chromatography-time of flight mass spectrometry, capillary electrophoresis-time of flight mass spectrometry, high performance liquid chromatography, and gas chromatography-mass spectrometry indicated that volatile and non-volatile metabolite profiles differed significantly between dark treated and untreated leaves.
Article
Carotenoid content of tea leaves ranges from 36 to 73 mg/100 g dry weight, and is dominated mainly by β-carotene, lutein and zeaxanthin. Among the cultivars, China contained the maximum and Assam clone the least. Carotenoid fractions were found to degrade to different extents at different stages of tea processing. The carotenoid content was as low as 25 mg/100 g in the made tea. Only a small quantity was leached into the brew, the remaining being retained in the infused leaf/tea residue. The high stability of carotenoid in tea is mainly due to the presence of antioxidants, such as polyphenols and catechins. Carotenoid degradation was found to be greater in the CTC (Crush, Tear, Curl) process than the orthodox process, greater in withered than unwithered, and in the order β-carotene > zeaxanthin > lutin. Vitamin A value was greater in orthodox tea than CTC tea and it varied with clones. The carotenoid degradation was found to yield large quantities of desirable aroma volatiles in made tea, giving a high grown flavour status. An increase in endogenous carotene content enhanced all the quality parameters of tea, the VFC (volatile flavour compounds) index, almost being doubled. The tasters' evaluation also revealed the same trend. It was found that a 1:1 NK application at the rate of 300 kg/ha/year enhanced the carotenoid content of green leaves in the second week after application, with subsequent decline.
Article
Together with a brief history of the development of simultaneous distillation–extraction (SDE), this review intends to provide the reader with practical guidelines that can be drawn from the literature, and to help the analyst in the choice of optimum experimental conditions adapted to a given sample preparation problem. This paper starts from the original apparatus of Likens and Nickerson, includes designs for micro-scale experiments, and ends up with the version operating under vacuum, and another for large-scale operations. The question of artifact formation is covered, together with proposed solutions for their prevention. Examples are given from applications in the field of flavours, fragrances and the environment. To better illustrate capabilities and limits of SDE, comparisons of SDE with other techniques of sample preparation are presented. Copyright © 2001 John Wiley & Sons, Ltd.
Article
 A compact and versatile distillation unit was developed for the fast and careful isolation of volatiles from complex food matrices. In connection with a high vacuum pump (5×10–3 Pa), the new technique, designated solvent assisted flavour evaporation (SAFE), allows the isolation of volatiles from either solvent extracts, aqueous foods, such as milk or beer, aqueous food suspensions, such as fruit pulps, or even matrices with a high oil content. Application of SAFE to model solutions of selected aroma compounds resulted in higher yields from both solvent extracts or fatty matrices (50% fat) compared to previously used techniques, such as high vacuum transfer. Direct distillation of aqueous fruit pulps in combination with a stable isotope dilution analysis enabled the fast quantification (60 min including MS analysis) of compounds such as the very polar and unstable 4-hydroxy-2,5-dimethyl-3(2H)-furanone in strawberries (3.2 mg/kg) and tomatoes (340 μg/kg). Furthermore, the direct distillation of aqueous foods, such as beer or orange juice, gave flavourful aqueous distillates free from non-volatile matrix compounds.
Article
Abiotic stress possesses serious threat to plant distribution and production. In response to stress, plants induce the expression of many genes that function to protect the cellular machinery from stress-induced damages. These genes are largely regulated by specific transcription factors (TFs). NAC family proteins are plant specific TFs implicated in diverse processes including development, and biotic and abiotic stress responses. The present work described (i) cloning of CsNAM-like protein gene from a tree crop tea [Camellia sinensis (L.) O. Kuntze], (ii) its cellular localization, and (iii) regulation of the gene by external cues. The gene had an open reading frame of 873 base pairs encoding 291 amino acids with calculated molecular weight of 33.4 kDa and an isoelectric point (pI) of 6.72. Expression characterization showed the gene to be induced by drought, osmoticum, salt, heat and hydrogen peroxide. During the period of active growth, CsNAM-like protein showed ubiquitous expression in all the tissues analyzed, with higher level of transcripts in stem, flower bud and mature leaf as compared to the root, young leaf and fruit. The common response of CsNAM-like protein to various cues suggests its important role in imparting tolerance against abiotic stress.