Improve Tea Quality Research Articles

Effect of withering/spreading on the physical and chemical properties of tea: A review.

Withering and spreading, though slightly differing in their parameters, share the same aim of moisture reduction in tea leaves, and they have a strong impact on the physical and chemical properties of tea. Even though researchers tend to pay close attention to the characteristic crafts of different teas, increasing investigations begin to focus on the withering process due to its profound effects on the composition and content of quality-related compounds. This review provides an overview of tea withering process to address questions comprehensively during withering. Hence, it is expected in this review to figure out factors that affect withering results, the way withering influences the physical and chemical properties of withered leaves and tea quality, and intelligent technologies and devices targeted at withering processes to promote the modernization of the tea industry. Herein, several key withering parameters, including duration, temperature, humidity, light irradiation, airflow, and more, are tailored to different tea types, demanding further exploration of advanced withering devices and real-time monitoring systems. The development of real-time monitoring technology enables objective and real-time adjustment of withering status in order to optimize withering results. Tea quality, including taste, aroma, and color quality, is first shaped during withering due to the change of composition and content of quality-related metabolites through (non)enzymatic reactions, which areeasily influenced by the factors above. A thorough understanding of withering is key to improving tea quality effectively and scientifically.

Comparison of Volatile Compounds among Four Types of Teas Analyzed Using Gas Chromatography-Ion Mobility Spectrometry.

Gas chromatography-ion mobility spectrometry (GC-IMS) is a smart method that has been applied to determine the volatile compounds in Chinese teas, but its use in comparing the volatile compounds of different types of tea has not been mentioned. In this study, the volatile compounds found in four types of samples (green, yellow, white, and black teas) made with fresh leaves of Camellia sinensis (L.) Kuntze 'Zhongcha 111' were analyzed using GC-IMS. The results showed that 93 volatile compounds were identified from our tea samples and that the average volume of aldehydes was higher than that for other compounds, especially in white tea. The different samples were successfully categorized using multivariate statistical analysis. Using partial least squares discriminant analysis (PLS-DA), we found 15 key compounds, including four differential components: (E)-2-hexenal, 2-furanmethanethio, 2-hexanol, and 1-octene. There were 29 common components, and their total content reached 386.0 μg/g. Moreover, the 3-methyl-2-butenal and dimethyl disulfide detected in the four samples were also differential compounds, varying according to the manufacturing technology. Thus, this study demonstrates that different types of teas can be discriminated easily using GC-IMS and that this is helpful to shorten the time for improving tea quality and developing new products.

Dynamic DNA Methylation Regulates Season-Dependent Secondary Metabolism in the New Shoots of Tea Plants.

Plant secondary metabolites are critical quality-conferring compositions of plant-derived beverages, medicines, and industrial materials. The accumulations of secondary metabolites are highly variable among seasons; however, the underlying regulatory mechanism remains unclear, especially in epigenetic regulation. Here, we used tea plants to explore an important epigenetic mark DNA methylation (5mC)-mediated regulation of plant secondary metabolism in different seasons. Multiple omics analyses were performed on spring and summer new shoots. The results showed that flavonoids and theanine metabolism dominated in the metabolic response to seasons in the new shoots. In summer new shoots, the genes encoding DNA methyltransferases and demethylases were up-regulated, and the global CG and CHG methylation reduced and CHH methylation increased. 5mC methylation in promoter and gene body regions influenced the seasonal response of gene expression; the amplitude of 5mC methylation was highly correlated with that of gene transcriptions. These differentially methylated genes included those encoding enzymes and transcription factors which play important roles in flavonoid and theanine metabolic pathways. The regulatory role of 5mC methylation was further verified by applying a DNA methylation inhibitor. These findings highlight that dynamic DNA methylation plays an important role in seasonal-dependent secondary metabolism and provide new insights for improving tea quality.

A simple fluorescent probe for selectively detecting Al3+ and F- in living cells and growing tea plants.

Aluminum (Al3+) and fluorine (F-) ions can be easily enriched in tea plants. When they excessively accumulate in tea, they can affect the health of tea lovers. Herein, a simple, highly sensitive and selective fluorescent probe (named BHMP) for Al3+ and F- detection was developed through a one-step condensation reaction, in which benzothiazole acted as a fluorophore and acceptor and hydrazine-Schiff base as a recognition unit. The probe was characterized comprehensively using spectroscopic methods, and the structure-activity relationship was systematically researched through crystal structure and theoretical calculations. Its sensitivity was measured via the fluorescent titration experiment, and the limit of detection (LOD) towards Al3+ was up to 1.04 × 10-8 mol L-1. Furthermore, we successfully utilized BHMP to visually detect the presence of Al3+ in living cells and tea tree roots through fluorescence confocal imaging. The successful detection of Al3+ in tea tree roots indicated that BHMP could be used as a candidate fluorescent chemosensor to dynamically monitor the variation in enriched Al3+ under the influence of the environment during tea tree growth. Our study provides a reference for the control of Al3+ concentration during the growth of tea plants and provides new insights into improving tea quality control.

Intercropped Flemingia macrophylla successfully traps tea aphid (Toxoptera aurantia) and alters associated networks to enhance tea quality.

The tea aphid, Toxoptera aurantia is a destructive pest causing severe damage to the quality and yield of tea, Camellia sinensis. Relying on chemical insecticides to control this pest causes adverse ecological and economic consequences. Trap plants are an eco-friendly alternative strategy to mitigate pest damage on focal plants by attracting target insects and natural enemies. Yet, the utilization of trap plants in tea plantations remains limited. Besides, the effects of the trap plant on the tea aphid-ant-predator community and tea quality and yield are unknown. Intercropped Flemingia macrophylla successfully trapped tea aphids and enhanced the complexity of aphid-ant-predator networks over three consecutive years compared to monoculture management. Moreover, F. macrophylla significantly increased the abundance of natural predators by 3100% and species richness by 57%. The increasing predators suppressed the aphid population and hampered its spillover to neighbouring tea plants. Consequently, F. macrophylla improved tea quality by an 8% increase in soluble sugar and a 26% reduction in polyphenols to amino acids ratio. The study illustrated that F. macrophylla is a suitable trap crop for tea aphid control in tea plantations. This legume increases species nodes and strengthens multiple connections in aphid-associated communities through its cascade effects, improving tea quality. These findings shed light on the potential application of trap plants in tea plantations as an efficient integrated pest management (IPM) strategy. © 2023 Society of Chemical Industry.

Improve tea quality by enhancing the stability of bacterial community interaction and nitrogen-fixing function in pecan-tea interplanted plantation

Using the 16 S rDNA high-throughput sequencing, the effects of interplanted pecan (Carya illinoinensis) in a typical tea (Camellia sinensis) plantation on soil bacterial species composition and marker species were comparatively analyzed to determine whether nested pecan increases soil microbial diversity in the tea tree rhizosphere. We explored the effects of the underlying mechanisms of this complex ecosystem on tea quality by determining soil physicochemical properties using two types of planting modes: intercropping with pecan versus tea tree monoculture. Our results showed that Rhizobium (Allorhizobium, Neorhizobium, Pararhizobium, and Rhizobium), and Enterobacter, had pollution-degrading effects and were enriched in the soil bacterial communities of the pecan interplanted model. There was a significant enrichment of prebiotic functional bacteria, such as Pedosphaeraceae and Coriobateriaceae_UCG-002, which stimulate plant growth and improve disease resistance, while the functions of Chloroflexi and Firmicutes, which are dominant denitrifying bacteria in the soil, were inhibited. The average degree of soil microbial co-occurrence network increased from 13.40 to 18.17, and the number of nodes in the network increased from 117 to 166, indicating that the network increased in complexity and decreased in mutual exclusivity, and the complex interactions among bacterial populations tended to be stable. The intercropping mode reduced the phenol/ammonia ratio in tea from 2.37 to 1.38, improving the tea quality. Therefore, the soil microbial community composition under this complex model promotes material cycling in microecosystems and effectively reduces the transmission risk of soil-borne diseases. The soil microbial community structure of the tea rhizosphere could be re-balanced and shifted toward a more favorable tea quality formation by the introduction of pecan into tea plantations.

Urate oxidase treatment increases the quality of autumn Yellowish Yinghong 9 black tea

Microbes can be used to improve the quality of fermented beverages and food. Colletotrichum camelliae is one of the most dominant fungi associated with tea leaves. In the present study, black tea produced from the autumn leaves of Yellowish Yinghong 9 was treated with C. camelliae urate oxidase (CcUOX) to determine whether this treatment could improve tea quality. The effects of recombinant CcUOX on several black tea quality parameters were assessed, such as liquor color, aroma, and levels of theabrownins, thearubigins, total polyphenols, catechins, caffeine, xanthine, and hypoxanthine. CcUOX treatment significantly affected the aroma composition and volatile compound profiles. Specifically, volatiles in the benzenoid/phenylpropanoid, fatty acid metabolism, and amino acid pathways were increased in CcUOX-treated black tea, whereas levels of volatiles in the terpineol and carotenoid pathways were reduced. This suggested that the balance of aroma constituents in Yellowish Yinghong 9 black tea was affected by treatment with CcUOX. The present study provides evidence that pre-treatment of black tea with a single enzyme from a common tea-associated microbe could significantly improve autumn tea quality, validating this method for use in further studies of tea improvement.

Study on taste quality formation and leaf conducting tissue changes in six types of tea during their manufacturing processes.

This study fristly investigated the taste quality formation and leaf conducting tissue changes in six types of Chinese tea (green, black, oolong, yellow, white, and dark) made from Mingke No.1 variety. Non-targeted metabolomics showed the vital manufacturing processes (green tea-de-enzyming, black tea-fermenting, oolong tea-turning-over, yellow tea-yellowing, white tea-withering, and dark tea-pile-fermenting) were highly related to their unique taste formation, due to different fermentation degree in these processes. After drying, the retained phenolics, theanine, caffeine, and other substances significantly impacted each tea taste quality formation. Meanwhile, the tea leaf conducting tissue structure was significantly influenced by high processing temperature, and the change of its inner diameter was related to moisture loss during tea processing, as indicated by its significantdifferent Raman characteristic peaks (mainly cellulose and lignin) in each key process. This study provides a reference for process optimization to improve tea quality.

Genome-Wide Investigation and Functional Analysis Reveal That CsKCS3 and CsKCS18 Are Required for Tea Cuticle Wax Formation.

Cuticular wax is a complex mixture of very long-chain fatty acids (VLCFAs) and their derivatives that constitute a natural barrier against biotic and abiotic stresses on the aerial surface of terrestrial plants. In tea plants, leaf cuticular wax also contributes to the unique flavor and quality of tea products. However, the mechanism of wax formation in tea cuticles is still unclear. The cuticular wax content of 108 germplasms (Niaowang species) was investigated in this study. The transcriptome analysis of germplasms with high, medium, and low cuticular wax content revealed that the expression levels of CsKCS3 and CsKCS18 were strongly associated with the high content of cuticular wax in leaves. Hence, silencing CsKCS3 and CsKCS18 using virus-induced gene silencing (VIGS) inhibited the synthesis of cuticular wax and caffeine in tea leaves, indicating that expression of these genes is necessary for the synthesis of cuticular wax in tea leaves. The findings contribute to a better understanding of the molecular mechanism of cuticular wax formation in tea leaves. The study also revealed new candidate target genes for further improving tea quality and flavor and cultivating high-stress-resistant tea germplasms.

Effects of processing procedures on the formation of aroma intensity and odor characteristic of Benshan tea (Oolong tea, Camellia sentences)

Benshan tea is a kind of oolong tea, and Benshan (Camellia sinensis) tea tree originates from Anxi County of Fujian Province in China, which is a national tea tree breed. Tea processing is the key to the formation of its odor characteristics. It is extremely important to step by step analyze effects of tea processing on aroma intensity and the formation of odor characteristics for optimizing tea processing process and improving tea quality. The results of this study showed that processing resulted in a significant increase in the content of volatile compounds in tea leaves, i.e., from 25.213 μg/kg to 111.223 μg/kg, in which the volatile compounds were mainly terpenoids. Secondly, the analysis found that 20 kinds of key compounds constituted to odor characteristics of Benshan tea leaves, among which geraniol, trans-β-ionone, gerol, citronellol, benzeneacetaldehyde, and trans-nerolidol were the most key six. Floral and fruity aromas, especially floral aroma, mainly formed odor characteristics of Benshan tea after processing, while floral aroma mainly came from the contribution of geraniol, which was the foremost compound in the formation of floral aroma of Benshan tea.

Understanding the Origin and Evolution of Tea (Camellia sinensis [L.]): Genomic Advances in Tea.

Tea, which is processed by the tender shoots or leaves of tea plant (Camellia sinensis), is one of the most popular nonalcoholic beverages in the world and has numerous health benefits for humans. Along with new progress in biotechnologies, the refined chromosome-scale reference tea genomes have been achieved, which facilitates great promise for the understanding of fundamental genomic architecture and evolution of the tea plants. Here, we summarize recent achievements in genome sequencing in tea plants and review the new progress in origin and evolution of tea plants by population sequencing analysis. Understanding the genomic characterization of tea plants is import to improve tea quality and accelerate breeding in tea plants.

γ-Glutamyl-transpeptidase CsGGT2 functions as light-activated theanine hydrolase in tea plant (Camellia sinensis L.).

Theanine is an important secondary metabolite endowing tea with umami taste and health effects. It is essential to explore the metabolic pathway and regulatory mechanism of theanine to improve tea quality. Here, we demonstrated that the expression patterns of CsGGT2 (γ-glutamyl-transpeptidase), participated in theanine synthesis in vitro in our previous research, are significantly different in the aboveground and underground tissues of tea plants and regulated by light. Light up-regulated the expression of CsHY5, directly binding to the promoter of CsGGT2 and acting as an activator of CsGGT2, with a negative correlation with theanine accumulation. The enzyme activity assays and transient expression in Nicotiana benthamiana showed that CsGGT2, acting as bifunctional protein, synthesize and degrade theanine in vitro and in planta. The results of enzyme kinetics, Surface plasmon resonance (SPR) assays and targeted gene-silencing assays showed that CsGGT2 had a higher substrate affinity of theanine than that of ethylamine, and performed a higher theanine degradation catalytic efficiency. Therefore, light mediates the degradation of theanine in different tissues by regulating the expression of the theanine hydrolase CsGGT2 in tea plants, and these results provide new insights into the degradation of theanine mediated by light in tea plants.

Integrative analyses of transcriptome and metabolome reveal comprehensive mechanisms of Epigallocatechin-3-gallate (EGCG) biosynthesis in response to ecological factors in tea plant (Camellia sinensis)

Epigallocatechin-3-gallate (EGCG), a flavoured and healthy compounds in tea, is affected by the ecological factors. However, the biosynthetic mechanisms of EGCG in response to the ecological factors remian unclear. In this study, a response surface method with a Box-Behnken design was used to investigate the relationship between EGCG accumulation and ecological factors; further, integrative transcriptome and metabolome analyses were performed to explore the mechanism underlying EGCG biosynthesis in response to environmental factors. The optimal environmental conditions obtained for EGCG biosynthesis were as follows: 28℃, 70 % relative humidity of the substrate, and 280 µmol·m−2·s−1 light intensity; the EGCG content was increased by 86.83 % compared to the control (CK1). Meanwhile, the order of EGCG content in response to the interaction of ecological factors was as follows: interaction of temperature and light intensity > interaction of temperature and relative humidity of the substrate > interaction of light intensity and relative humidity of the substrate, indicating that temperature was the dominant ecological factors. EGCG biosynthesis in tea plants was found to be comprehensively regulated by a series of structural genes (CsANS, CsF3H, CsCHI, CsCHS, and CsaroDE), miRNAs (miR164, miR396d, miR5264, miR166a, miR171d, miR529, miR396a, miR169, miR7814, miR3444b, and miR5240), and transcription factors (MYB93, NAC2, NAC6, NAC43, WRK24, bHLH30, and WRK70); further, the metabolic flux was regulated and converted from phenolic acid to the flavonoid biosynthesis pathway based on accelerated consumption of phosphoenolpyruvic acid, d-erythrose-4-phosphate, and l-phenylalanine in response to ambient changes in temperature and light intensity. Overall, the results of this study reveal the effect of ecological factors on EGCG biosynthesis in tea plants, providing novel insights for improving tea quality.

Effects of Soil Physical and Chemical Properties on the Quality of Nanjing ‘Yuhua’ Tea, a Type of Famous Green Tea

Tea has become one of the most popular drinks worldwide because of its special taste and health benefits. ‘Yuhua’ tea is a famous specialty of Nanjing, China, a green tea produced from Camelia sinensis. It belongs to the green tea category and is one of the top ten most famous teas in China. The physical and chemical properties of soil are very important to the quality of tea. However, at present, there are few instances of research on the soil of the ‘Yuhua’ tea cultivation area. To provide the theoretical basis for improving the final quality of ‘Yuhua’ tea by soil management measures, the effects of the soil’s physical and chemical properties on the contents of important chemical components (free amino acids, tea polyphenols, and caffeine) of ‘Yuhua’ tea in three different cultivation areas in Nanjing were studied. The quality of ‘Yuhua’ tea is greatly influenced by the physical and chemical properties of the soil in which the tea plant grows. The free amino acid content and tea polyphenol content of tea leaves were significantly and negatively correlated with soil bulk density, pH, and water-soluble calcium content, while a significantly positive correlation was noticed between the two criteria and soil effective nitrogen, phosphorus, and potassium content. Additionally, the growth of the tea tree will be hampered and perhaps stressed if the soil’s helpful mineral concentration is too low. The tea tree may produce more caffeine as a result, which could lower the quality of the tea leaves. Therefore, implementing targeted soil management techniques is the key to promoting tea tree growth and improving tea quality. This study laid the foundation for the adoption of corresponding soil management measures to improve the quality of ‘Yuhua’ tea.

Transcriptome Analysis of 5-Aminolevulinic Acid Contributing to Cold Tolerance in Tea Leaves (Camellia sinensis L.)

Tea (Camellia sinensis L.) is an important perennial cash crop and a typical subtropical plant. It is widely concerned because of its unique flavor and health benefits. In recent years, low temperatures have severely restricted the growth of tea plants and quality of tea products, especially in spring. As a common precursor for all porphyrin compounds, 5-aminolevulinic acid (ALA) is involved in photosynthesis and respiration and plays an active role in improving salt, drought and low-temperature tolerance in plants. However, it is not yet clear what affect exogenous ALA has on tea plants’ tolerance under low temperature. In the present study, we collected and deciphered the transcriptome profiles from Shaancha No. 1 leaf tissues under low temperature (−4 °C) treatment (T-4), exogenous ALA application (T-A), pretreated ALA before low temperature (T-A-4) and untreated control (T-CK). Results showed that 4990 (2375 up- and 2615 down-regulated), 223 (103 up- and 120 down-regulated) and 92 (13 up- and 79 down-regulated) differentially expression genes (DEGs) were identified at T-CK vs. T-4, T-CK vs. T-A and T-4 vs. T-A-4, respectively. Both T-4 and T-A treatments triggered a myriad of stress resistance genes up-regulated related to multiple signaling pathways by means of Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. This included MAPK, a toll-like receptor that signals pathways involved in cold resistance. However, gene ontology (GO) analysis showed that the DEGs in T-4 treatment were mainly enriched in the phenylpropanoid metabolic and redox processes that were relevant to membrane structure damage response. In contrast, the DEGs in T-A treatment were mainly enriched in cell recognition and amylase activity. Furthermore, in pairwise comparison of T-A-4 vs. T-4, the DEGs were enriched in ascorbate and aldarate, retionol, taurine and hypotaurine, glutathione metabolic pathways and two biosynthesis process including zeatin, diterpenoid biosynthesis, which might contribute to mitigating the damage caused by low temperature. Overall, these results indicated that exogenous ALA application may improve the biochemical attributes and enhance the tolerance to low temperature, which provides a valuable strategy to improve tea quality and cold stress.

Shading effects revisited: Comparisons of spring and autumn shading treatments reveal a seasonal-dependent regulation on amino acids in tea leaves

Shading is an effective way to improve tea quality by modulating the accumulation of the flavor-related secondary metabolites of tea leaves. However, shading effects on amino acids have been conflicting for years as both shading-induced increases and decreases were detected. This study aims to investigate the effects of shading levels on catechins and amino acids, in particular, a comparison was made in April and August to better understand the involvements of seasonal environmental parameters. Shading reduced major catechins (catechin, gallocatechin, epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate) in both seasons. Heavy shading (80%-90%) increased total and individual amino acids (Threonine, Glutamic acid, and Alanine) in April but decreased those in August. In both seasons, the o-Phosphoethanolamine increased under heavy shading, but α-aminoadipic acid, Ornithine and Glutamine showed decreases. Theanine showed no shading response in April but decreased under heavy shading in August. These results indicate that shading-induced reduction of leaf catechins is mainly determined by shading level, but the shading effects on amino acids are seasonal-dependent. As the first report focuses on the synergistic effects of seasons, this study improves our understanding of shading regulation on secondary metabolites of tea leaves and guides shading treatments to improve tea quality.

Tea pruning for the umbrella-shaped canopy can alleviate rhizosphere soil degradation and improve the ecosystem functioning of tea orchards

Leaf and branch pruning is essential for improving the productivity of continuously cropped leaf-harvested crops, such as tea, which is conductive to stabilize the production, delay the aging, and subsequently improve economic benefits. Generally, farmers adopt crew-cut pruning to get more yield in tea orchard pruning management. However, the long-term effects of crew-cut pruning on ecosystem of tea orchard are unclear. The present study investigated the environmental differences of ecosystem between crew-cut tea (CT) pruning and umbrella-shaped tea (UT) pruning treatments in the Tieguanyin tea orchards of China. We analyzed the soil enzymes activities, the rhizosphere and phyllosphere's microbial communities, the secondary metabolites of fresh tea shoots, and the insect abundance and its diversity in the two types of tea orchards. The results showed that both saccharase and urease were improved at different soil layers by UT. Fresh tea shoots analysis revealed 22.91% and 16.59% higher epigallocatechin gallate and epicatechin gallate levels, respectively under UT regime than those in CT, but a 9.42% lower ratio of polyphenol to the amino acid in comparision with that in CT. The total volatiles, especially (E)-geraniol and furanoid linalool oxides, in the fresh shoots of UT were also significantly higher than those in CT. Further analysis showed that UT had more beneficial insects than CT. In contrast, tea gardens in CT were at a higher risk of pest attack than that in UT. Prolonged umbrella pruning of tea plantations significantly improved the bacterial diversity and the beneficial fungi in the leaf surface. Moreover, the relative abundances of rhizobia and ammonia-oxidizing bacteria in the rhizosphere were higher in UT than that in CT. The findings suggest that tea pruning in umbrella-shaped can reduce rhizosphere soil degradation and improve the ecosystem functioning, suggesting that proper pruning pattern is needed to improve tea quality.

Pea-Tea Intercropping Improves Tea Quality through Regulating Amino Acid Metabolism and Flavonoid Biosynthesis.

Pea-tea intercropping is an excellent cultivation method that can improve tea quality. However, the underlying mechanism is still unclear. The present study was aimed at elucidating the mechanism of the effect of pea-tea intercropping on tea quality through a high-throughput method. Transcriptome and metabolome analyses were conducted to identify the changes in gene expression and metabolites changes intercropping, respectively. In addition, the amino acids and catechins were detected using the LC-MS method and quantified absolutely. The results showed that total polyphenols and catechins decreased but amino acids increased in pea intercropped tea shoots. Correspondingly, genes related to amino acid metabolism and flavonoid biosynthesis were differentially expressed. For amino acid metabolism, 11 differentially expressed genes were identified, including 5 upregulated and 6 downregulated genes. Meanwhile, three genes involved in carbohydrate transport and metabolism were upregulated in pea intercropped tea plants. These genes were also involved in amino acid metabolism. For flavonoid biosynthesis, two downregulated genes were identified, which were the flavonol synthase and anthocyanidin synthase genes and followed a similar pattern to changes in catechins and polyphenols. These advances have opened new horizons for understanding the biochemical mechanisms of amino acids and flavonoids in improving tea quality in the pea-tea intercropping cultivation model.

Using surface-enhanced Raman spectroscopy combined with chemometrics for black tea quality assessment during its fermentation process

Developing a reliable and convenient method for monitoring the quality of black tea during fermentation could lead to a significant improvement in fermentation process. This work presented a rapid method based on surface-enhanced Raman spectroscopy (SERS) technology and chemometrics to determine the optimal fermentation stage and monitor the changes in 10 types of quality indicators of black tea throughout fermentation. First, the 10 different fermentation time points were clustered into 5 fermentation stages. Based on the SERS data, the fermentation stages were distinguished with an accuracy of 83.33 % by one-dimensional ResNet18 (1D-ResNet18). Furthermore, important Raman peaks at 317.71, 619.59, 731.48, 956.08 and 1326.70 cm-1 were found for monitoring quality changes of black tea by density functional analysis and correlation analysis. The prediction r2 for catechin (C) and epigallocatechin gallate (EGCG) reached 0.81 and 0.82, respectively, by integrated SERS with a one-dimensional convolutional neural network (1D-CNN). In conclusion, this study revealed the Raman fingerprint characteristics of key compounds associated with the fermentation quality of black tea, presenting an opportunity to quantify the quality changes of tea during fermentation using SERS data. With the monitoring method developed in this research, the optimal fermentation stage can be determined accurately, thus decreasing fermentation costs and improving tea quality.

Dynamic Changes in the Antioxidative Defense System in the Tea Plant Reveal the Photoprotection-Mediated Temporal Accumulation of Flavonoids under Full Sunlight Exposure.

To reveal the mechanisms underlying how light affects flavonoid metabolism and the potential role of flavonoids in protecting against photooxidative stress in tea leaves, tea plants adapted to low-light conditions were exposed to full sunlight over 48 h. There was an increase in the activities of catalase (CAT) and superoxide dismutase (SOD) as well as greater accumulation of reactive oxygen species, lutein, tocopherols, ascorbate and malondialdehyde, suggestive of a time-dependent response to photooxidative stress in tea leaves. Analysis of the time dependency of each element of the antioxidant system indicated that carotenoids and tocopherols exhibited the fastest response to light stress (within 3 h), followed by SOD, CAT and catechin, which peaked at 24 h. Meanwhile, flavonols, vitamin C and glutathione showed the slowest response. Subsequent identification of the main phytochemicals involved in protecting against oxidative stress using untargeted metabolomics revealed a fast and initial accumulation of nonesterified catechins that preceded the increase in flavonol glycosides and catechin esters. Gene expression analysis suggested that the light-induced accumulation of flavonoids was highly associated with the gene encoding flavonol synthase. Ultraviolet B (UV-B) irradiation further validated the time-dependent and collaborative effects of flavonoids in photoprotection in tea plants. Intriguingly, the dynamics of the metabolic response are highly distinct from those reported for Arabidopsis, suggesting that the response to light stress is not conserved across plants. This study additionally provides new insights into the functional role of flavonoids in preventing photooxidative stress and may contribute to further improving tea quality through the control of light intensity.