Tea Polyphenols Research Articles

Fabrication, characterization, and bioactivity of self-assembled carrier-free colloidal dispersions from Citrus × Limon ‘Rosso’ essential oil and tea polyphenols

Carrier-free nanodelivery systems are fully self-assembled from active ingredients through interactions, offering the advantages of green, safe, and large-scale manufacturing. To improve the dispersion of Citrus × limon ‘Rosso’ peel essential oil (CEO) in water and boost the biological activity of CEO and tea polyphenols (TP), self-assembled CEO-TP colloidal dispersions (CEO-TP Colloids) were fabricated through sonication without surfactants or carriers. The optimal CEO and TP concentrations in the CEO-TP Colloids were determined to be 10.0 and 20.0 mg/mL by particle size and stability analyzer, respectively. The CEO self-assembled with TP to form spherical nanoparticles through hydrophobic and hydrogen-bonding interactions, whereas the CEO in CEO-TP Colloids weakened TP intramolecular aggregation. Meanwhile, the CEO-TP Colloids showed synergistic effects with better antibacterial, cellular antioxidant, and anti-inflammatory activities than single components. This study opens up the possibility of carrier-free co-delivery of hydrophobic and hydrophilic active components developed into food-grade formulations with multiple bioactivities.

Green tea polyphenols reduced Porphyromonas gingivalis virulence and ameliorated aggravated gut inflammation by improving immunity and gut microbiota dysbiosis

Porphyromonas gingivalis (PG), a key periodontal pathogen, has been implicated in various systemic diseases, including colorectal cancer and cardiovascular diseases. However, its potential role in promoting gut inflammation and the underlying mechanisms remain unclear. Furthermore, multiple studies have reported an association between tea polyphenols and a reduced risk of periodontal disease and colitis, but it remains unclear whether they play a role in mitigating gut inflammation exacerbated by PG. In this study, we demonstrated that Tea polyphenols (TP) reduced the activity of PG and lowered the expression levels of virulence factors. Intervention with TP can prevent the worsening of gut inflammation exacerbated by PG, including body weight loss and shortened colon length. TP not only alleviated the differentiation of Th17 cells and the secretion of related cytokines but also promoted the enrichment of potentially beneficial bacteria like Ruminococcus and Lactobacillus. Metabolomics revealed that TP enriched potential beneficial microbial metabolites, such as secondary bile acids, and showed certain correlations with immune-related markers.

Fabrication of an antibacterial system of arginine-modified chitosan with AgNPs-loaded montmorillonite for food preservation

Ag-based materials have potent antibacterial effects, but their potential toxicity problems should not be underestimated, so it is urgent to construct a safe and non-resistant dual antibacterial system. In this study, we utilized tea polyphenols (TPs) and montmorillonite (MMT) to control the growth of silver nanoparticles (AgNPs). Then, we combined the AgNPs with arginine to construct a synergistic antibacterial system of arginine-modified chitosan-assisted AgNPs-loaded MMT (ACS/G/AgNPs@MMT). The results showed that AgNPs with a uniform dispersion of 6.72 ± 4.66 nm and ACS with a grafting degree of 0.153 were successfully prepared, and the synergistic antibacterial effect between ACS and AgNPs@MMT was verified by the FIC index, and the antibacterial rate could still reach 99.9 % when the additions of ACS and AgNPs@MMT were reduced by 75 % and 79.1 %, respectively. The ACS/G/AgNPs@MMT-2 composite film exhibited excellent mechanical properties, water vapor/UV barrier properties, antioxidant activity, degradation properties, and biosafety. In addition, the synergistic effect enabled the ACS/G/AgNPs@MMT-2 film to achieve antibacterial rates of 99.24 ± 0.19 % against E. coli and 99.49 ± 0.40 % against S. aureus, and the film exhibited excellent long-lasting antibacterial performance due to the slow release of Ag+ (only about 11.27 % of Ag+ was released in 20 days). Finally, the ACS/G/AgNPs@MMT-2 film could significantly improve the food preservation ability. In conclusion, this study indicates that the film could be used as a novel antibacterial packaging material.

Selenium-Mediated (-)-Epigallocatechin-3-Gallate Dynamics via Flavanone-3-Hydroxylase Regulation of Flavonoid Biosynthesis in Fu Tea (Camellia sinensis (L.) O. Kuntze).

Tea (Camellia sinensis (L.) O. Kuntze) is a highly selenium enrichment capacity plant; high selenium concentration contributes to the occurrence of oxidative stress and protein misfolding in tea plants, whereas flavonoids can chelate heavy metals to protect plants from oxidative stress caused by metal exposure. Nevertheless, the role of catechins in flavonoid synthesis and nutrient metabolism under selenium stress remains unidentified. Combining Word2vec and HNSW utilizing UHPLC-Q-Orbitrap HRMS-MS/MS to implement rapid matching annotation of the structural information on metabolites in Fu tea, we found that selenium-mediated changes in catechins in Fu tea were mainly associated with flavonoid biosynthesis pathways. The results demonstrated that selenium treatment increased benign selenol analogues (glutathioselenol) in tea and identified the novel selenopeptide PRSeMW (m/z 636.22571, Pro-Arg-SeMet-Trp) in selenium-enriched Fu tea samples to enhance the health benefits of tea. The selenium levels were negatively correlated with N5-ethyl-l-glutamine (11.63 to 4.26 mg kg-1) and (-)-epigallocatechin (13.26 to 11.19 mg kg-1), increasing the accumulation of tea polyphenols ((-)-catechin gallate, (-)-epigallocatechin 3-gallate, and (+)-gallocatechin), and decreasing the level of caffeine. These discoveries provide new insights into the mechanism of tea polyphenol-mediated transformation of selenium in Fu tea and theoretical support for the quality assessment of selenium-enriched tea.

Aloe vera and tea polyphenols composite coating delays passion fruit senescence by promoting phenolic and flavonoid accumulation

Passion fruits are highly perishable during postharvest storage and transportation, prompting the exploration of natural preservatives. This study investigates the synergistic effects of Aloe vera (ALV) and tea polyphenols (TP) coatings on quality retention, ripening modulation, and associated regulatory mechanisms in stored “golden” passion fruit (Passiflora spp.) at 10 °C. The application of a composite coating comprising 40 % ALV and 0.1 g/L TP led to notable improvements in fruit preservation over a 28-day storage period. At the day of 28, quantitatively, the ALV + TP treatment reduced weight loss by 41.60 %, shrinkage index by 28.13 %, and decay index by 50 %, significantly outperforming the control and individual treatments; the treated fruits exhibited enhanced firmness, reduced ethylene production, and the respiration peak was delayed about 6 days. Metabolomic analysis revealed pronounced alterations in key metabolic pathways, notably phenylpropanoid and flavonoid biosynthesis. Specifically, significant increases in metabolites such as phenolic acids (Feruloylmalic acid and Acropyrone) and flavonoids (Okanin-4’-O-glucoside, Apigenin-8-C-Arabinoside, Quercetin-3-O- (2’-O-galloyl) galactoside, and Catechin callate) were observed. Concurrently, transcript levels of key biosynthetic genes including cinnamate 4-hydroxylase (PeC4H), 4-coumarate-coenzyme a ligase (PeC4L), hydroxycinnamoyl transferase (PeHCT) and flavonol synthase (PeFLS) were significantly up-regulated by ALV + TP coating, indicating a robust activation of these pathways. The findings underscore the effectiveness of the ALV + TP composite coating as an environmentally friendly strategy for enhancing postharvest quality by promoting the accumulation of beneficial phenolic acids and flavonoids in passion fruits.

Constructing Single- or Dual-Layer Biomass Composite Energetic Material through Self-Assembly of Biomass Polyphenol Structural Materials.

High energy and high risk have always restricted the application of materials in the military and civilian fields. To achieve this goal, researchers have studied the structural characteristics and structure-activity relationship of biomass polyphenol material to obtain core-shell biomass polyphenol composite energetic materials through molecular and structural design. The interface structure has a significant impact on the safety performance and thermal stability of energetic materials. The unique advantages of natural biomass polyphenol chemistry (tannic acid and tea polyphenols) include the structural design and performance control of energetic materials. This paper provides a review of the preparation of core-shell biomass polyphenol energetic materials, which involve the use of polyphenols as the shell layer, surface modification layer, and intermediate layer to enhance intermolecular interactions. This approach aims to enhance the thermal stability and reduce the sensitivity. Furthermore, the paper offers suggestions for potential future research directions based on the findings.

Epigallocatechin gallate modulates ferroptosis through downregulation of tsRNA-13502 in non-small cell lung cancer

Ferroptosis, an iron-dependent regulated cell death mechanism, holds significant promise as a therapeutic strategy in oncology. In the current study, we explored the regulatory effects of epigallocatechin gallate (EGCG), a prominent polyphenol in green tea, on ferroptosis and its potential therapeutic implications for non-small cell lung cancer (NSCLC). Treatment of NSCLC cell lines with varying concentrations of EGCG resulted in a notable suppression of cell proliferation, as evidenced by a reduction in Ki67 immunofluorescence staining. Western blot analyses demonstrated that EGCG treatment led to a decrease in the expression of glutathione peroxidase 4 (GPX4) and solute carrier family 7 member 11 (SLC7A11) while increasing the levels of acyl-CoA synthetase long-chain family member 4 (ACSL4). These molecular changes were accompanied by an increase in intracellular iron, malondialdehyde (MDA), and reactive oxygen species (ROS), alongside ultrastructural alterations characteristic of ferroptosis. Through small RNA sequencing and RT-qPCR, transfer RNA-derived small RNA 13502 (tsRNA-13502) was identified as a significant target of EGCG action, with its expression being upregulated in NSCLC tissues compared to adjacent non-tumorous tissues. EGCG was found to modulate the ferroptosis pathway by downregulating tsRNA-13502 and altering the expression of key ferroptosis regulators (GPX4/SLC7A11 and ACSL4), thereby promoting the accumulation of iron, MDA, and ROS, and ultimately inducing ferroptosis in NSCLC cells. This study elucidates EGCG’s multifaceted mechanisms of action, underscoring the modulation of ferroptosis as a viable therapeutic approach for enhancing NSCLC treatment outcomes.

Tumor microbiota affects the efficacy of tea polyphenols therapy in breast tumor

The therapeutic efficacy of tea polyphenols (TP) has been demonstrated in various tumor types, and research has indicated its potential role in modulating the intestinal microbiota. However, the impact of it on tumor microbiota remains uncertain. The research aimed to investigate how TP treatment affects microorganisms in breast tumors (4T1) and explore their potential influence on the TP's therapeutic efficacy. The TP significantly inhibited the growth of 4T1 tumors, and DOX-TP significantly enhanced the efficacy of TP against the tumors, whereas DOX alone did not show similar effects. The results of 16 S rDNA sequences indicated that Herbaspirillum, Herminiimonas, Stenotrophomonas exhibited a remarkable increase (regulation rate≥99.72% and the abundance up-regulation by 7.91%, 5.17% and 5.77%, respectively), transitioning from absence to presence in the TP group to the DOX-TP group. Conversely, Halomonas, ZOR0006, Hydrogenophilus, Rhodococcus, Vibrio were significantly decreased (regulation rate≥99.91% and the abundance down-regulation by 3.16%, 2.78%, 3.15%, 12.92% and 16.03%, respectively) after DOX-TP treatment, resulting in a shift from presence to absence. Compared to the TP group, DOX-TP group demonstrated enhanced infiltration of CD4+ T and CD8+ T cells, while exhibiting significantly elevated expression levels of IL-2, IFN-α, IFN-γ and TNF-α. Additionally, Rhodococcus and Halomonas were observed to be negatively correlated with IFN-α expression. The co-administration of TP and antibiotics further modified the tumor microbiota composition, influencing the tumor immune microenvironment. The study demonstrated that DOX-TP can enhance TP's anticancer effect by modulating the tumor microbiota.

Colorimetric array sensor based on bimetallic nitrogen-doped carbon-based nanozyme material to detect multiple antioxidants.

Copper-cobalt bimetallic nitrogen-doped carbon-based nanoenzymatic materials (CuCo@NC) were synthesized using a one-step pyrolysis process. A three-channel colorimetric sensor array was constructed for the detection of seven antioxidants, including cysteine (Cys), uric acid (UA), tea polyphenols (TP), lysine (Lys), ascorbic acid (AA), glutathione (GSH), and dopamine (DA). CuCo@NC with peroxidase activity was used to catalyze the oxidation of TMB by H2O2 at three different ratios of metal sites. The ability of various antioxidants to reduce the oxidation products of TMB (ox TMB) varied, leading to distinct absorbance changes. Linear discriminant analysis (LDA) results showed that the sensor array was capable of detecting seven antioxidants in buffer and serum samples. It could successfully discriminate antioxidants with a minimum concentration of 10nM. Thus, multifunctional sensor arrays based on CuCo@NC bimetallic nanoenzymes not only offer a promising strategy for identifying various antioxidants but also expand their applications in medical diagnostics and environmental analysis of food.

Modulation of UVB-induced oxidative stress and inflammation in skin keratinocytes (HaCaT) utilising unfermented rooibos and honeybush aqueous extracts

Exposure to Ultraviolet B (UVB) radiation can trigger a diverse array of biological responses that have the potential to contribute to the onset of skin cancer. Natural compounds, such as tea polyphenols, have been shown to protect against UVB-induced damage by modulating oxidative stress, inflammatory response, and cell proliferation. The chemopreventive and anti-inflammatory properties of South African rooibos (Aspalathus linearis) and honeybush (Cyclopia spp.) herbal teas have been shown to mainly target the early stages of cancer development through mechanisms that involve intracellular interleukin-1α (IL-1α) inhibition. Thus, the aim was to investigate the preventive effects of unfermented rooibos and honeybush aqueous extracts against UVB-induced oxidative stress and inflammation in HaCaTs. Honeybush was found to reduce the accumulation of UVB-induced IL-1α while maintaining cell viability and without affecting apoptosis. Furthermore, only honeybush extract was able to decrease the secretion of interleukin-6 (IL-6) caused by UVB exposure. Honeybush and rooibos extracts significantly decreased the secretion of UVB-induced interleukin-8 (IL-8). Except for rooibos extract at a concentration of 0.2 mg/mL, both extracts restored the expression of antioxidant genes to levels observed prior to UVB exposure. The anti-inflammatory effects of these herbal tea extracts are likely attributed to the antioxidant properties of their polyphenolic constituents, which modulate the oxidative stress-induced pathways governing inflammatory responses.

Protection against oxidative DNA damage: Green tea polyphenols in Hsd:ICR mice exposed to hexavalent chromium

Protection against oxidative DNA damage: Green tea polyphenols in Hsd:ICR mice exposed to hexavalent chromium

Synergistic mixture of Camellia Oleifera shell extract and KI as an eco-friendly and highly efficient composite inhibitor for steel corrosion in H2SO4 media

To address the severe corrosion problems faced by steel, a natural corrosion inhibitor derived from Camellia Oleifera shell extract (COSE) was developed. The effectiveness of COSE as well as its synergistic mixture of COSE/KI in inhibiting the corrosion of steel in H2SO4 was investigated using weightlessness and electrochemical techniques. The results show that the maximum inhibition efficiency of individual COSE is 77.28 % at 20 °C, and is increased to 93.08 % for the mixture of COSE/KI. The adsorption of COSE, KI and COSE/KI on steel surface conform to Langmuir adsorption isotherm. COSE/KI has a stronger adsorption than either COSE or KI. Electrochemical analysis indicates that COSE/KI is a hybrid inhibitor primarily focusing on the cathodic inhibition. Mixing COSE with KI shows considerably larger charge transfer resistance and smaller double-layer capacitance than individual COSE and KI. Characterization tests such as metallurgical microscopy, SEM, AFM and contact angle confirm that the addition of COSE/KI could reduce the roughness of steel surface, while increase the hydrophobicity, then effectively alleviate the corrosion on the steel surface. XPS analyses demonstrated that the corrosion inhibition layer on the steel surface was induced by the adsorption of the polar groups in COSE. The components responsible for COSE’s effectiveness were thoroughly examined using FTIR and liquid chromatography-mass spectrometry (LC-MS), which identified the presence of compounds such as flavonoids and phenylpropanoids. The synergistic effect of the active ingredients (rutin, quercetin, tea saponin, tea polyphenols, et al.) with KI was also confirmed. Finally, theoretical calculations were conducted to analyze properties of rutin, quercetin and tea polyphenols on the iron layer. The results show all these molecules exhibit efficient inhibition, with quercetin showing better inhibitive ability by parallel adsorption.

EGCG Suppresses Adipogenesis and Promotes Browning of 3T3-L1 Cells by Inhibiting Notch1 Expression.

With the changes in lifestyle and diet structure, the incidence of obesity has increased year by year, and obesity is one of the inducements of many chronic metabolic diseases. Epigallocatechin gallate (EGCG), which is the most abundant component of tea polyphenols, has been used for many years to improve obesity and its complications. Though it has been reported that EGCG can improve obesity through many molecular mechanisms, EGCG may have many mechanisms yet to be explored. In this study, we explored other possible mechanisms through molecular docking and in vitro experiments. AutoDock Vina was selected for conducting the molecular docking analysis to elucidate the interaction between EGCG and Notch1, while molecular dynamics simulations were employed to validate this interaction. Then, the new regulation mechanism of EGCG on obesity was verified with in vitro experiments, including a Western blot experiment, immunofluorescence experiment, oil red O staining, and other experiments in 3T3-L1 adipocytes. The molecular docking results showed that EGCG could bind to Notch1 protein through hydrogen bonding. In vitro cell experiments demonstrated that EGCG can significantly reduce the sizes of lipid droplets of 3T3-L1 adipocytes and promote UCP-1 expression by inhibiting the expression of Notch1 in 3T3-L1 adipocytes, thus promoting mitochondrial biogenesis. In this study, molecular docking and in vitro cell experiments were used to explore the possible mechanism of EGCG to improve obesity by inhibiting Notch1.

UNDERSTANDING THE IMPACT OF UV RADIATION ON SKIN HEALTH: MECHANISMS, RISKS, AND PHOTOPROTECTION STRATEGIES

This comprehensive review examines the intricate relationship between UV radiation and skin health, delving into its mechanisms, associated risks, and potential photoprotection strategies. Drawing from centuries of herbal medicine and cosmetic practices, the efficacy of antioxidant-rich herbs in shielding against UV radiation-induced damage is highlighted. Studies showcasing the protective properties of plant extracts, such as green and black tea polyphenols and aloe vera formulations, underscore the potential of botanicals in skincare. The rise of herbal sunscreens in response to growing concerns over UV exposure reflects a paradigm shift in skincare practices. The review elucidates the diverse effects of UV radiation on the skin, encompassing sunburns, premature aging, and skin cancer development. Mechanisms underlying UVB-induced skin damage, including collagen breakdown, generation of free radicals, and interference with DNA repair mechanisms, underscore the imperative of implementing protective measures. The role of antioxidants in mitigating UV-induced damage and the development of innovative sunscreen formulations underscores ongoing efforts to enhance photoprotection strategies. Furthermore, the review underscores the multifaceted nature of UV radiation’s impact on skin health, emphasizing the importance of holistic approaches to photoprotection.Future research endeavors aimed at exploring novel photoprotective agents and assessing their efficacy in preserving skin health will be instrumental in mitigating the adverse effects of UV radiation and fostering overall skin well-being.

Microbial community diversity during algal inhibition using slow-release microcapsules of tea polyphenols

Harmful algal blooms (HABs) resulting from eutrophication pose a major threat to ecosystems and human health, necessitating effective control measures. Allelochemicals have shown their importance in slowing down algal proliferation due to their proven efficacy and low ecological impacts. In this study, allelopathy tea polyphenols (TPs) and β-cyclodextrin were combined to prepare slow-release algicidal microcapsules, and the diversity of microbial community in the algal inhibition process was analyzed. Results showed that TP slow-release microcapsules had strong algicidal activity. When against Microcystis aeruginosa within 20 d, their constant inhibitory rate was up to 99% compared to the control group. Microbial diversity decreased with an increase in algae density, and the species richness and diversity of algae increased under the stress of TP slow-release microcapsules. The redundancy analysis showed that the environmental factors with impacts on the abundance and diversity of bacterial communities in descending order were dissolved oxygen, pH, and temperature. This study provides a theoretical basis for the application of TP slow-release microcapsules to actual water.

Development of interpenetrating network hydrogels: Enhancing the release and bioaccessibility of green tea polyphenols

Green Tea polyphenols (GTP) are important bioactive compounds with excellent physiological regulation functions. However, they are easily destroyed by the gastric environment during digestion. In this work, a sodium alginate (SA)-gellan gum (GG) interpenetrating network (IPN) hydrogel was synthesized to protect and delivery GTP. The ratio of SA/GG significantly affects the network structure of IPN hydrogels and the performance of delivering GTP. The hydrogel formed by interpenetrating 20 % GG with 80 % SA as the main network had the highest water uptake (55 g/g), holding capacity (950 mg/g), and freeze-thaw stability, with springiness reaching 0.933 and hardness reaching 1300 g, which due to the filling effect and non-covalent interaction. Rheological tests showed that the crosslink density of IPN hydrogel in SA-dominated network was improved by the addition of GG to make it better bound to GTP, and the higher water uptake meant that the system could absorb more GTP-containing solution. This IPN hydrogel maintained 917.3 mg/g encapsulation efficiency at the highest loading capacity (1080 mg/g) in tests as delivery system. In in vitro digestion simulations, owing to the pH responsiveness, the IPN hydrogel reduced the loss of GTP in gastric fluid, achieving a bioaccessibility of 71.6 % in the intestinal tract.

Assessing the Effects of Dietary Tea Polyphenols on the Gut Microbiota of Loaches (Paramisgurnus dabryanus) under Chronic Ammonia Nitrogen Stress

This study examined the impact of tea polyphenols (TPs) on the intestinal flora of loaches (Paramisgurnus dabryanus) under chronic ammonia nitrogen stress using high-throughput sequencing. Two groups of 600 loaches were studied over one month, and they were separated into a control group and tea polyphenol group. Alpha and beta diversity analyses showed diverse bacterial communities, with significant differences in the abundance and uniformity observed initially but not between sampling time points. Cluster analyses revealed distinct differences in microbial communities between groups. A predictive function analysis indicated enrichment in pathways related to amino acid and nucleotide biosynthesis. These findings offer initial insights into how tea polyphenols may affect intestinal microbial communities in loaches under ammonia nitrogen stress.

Effect of tea polyphenols on the quality of Mackerel puree (Scomber scombrus) during refrigerated storage: Color, oxidative stability and microstructure

This study investigated the impact of adding tea polyphenols (TP) on the quality of mackerel puree during refrigerated storage. The study used whole mackerel fish and analyzed the sensory characteristics, physicochemical properties, and microstructure of the puree. As storage time increased, significant changes occurred in the puree, including increased levels of thiobarbituric acid value, protein carbonyl, and free radicals. The water holding capacity, whiteness, and pH value of the puree decreased. However, the addition of TP helped to preserve the quality of the mackerel puree, particularly in the later stages of storage. This was evidenced by reduced oxidation of lipids and proteins, minimal color change, and a more compact microstructure. The study also revealed that TP contributes to the development of a gel network within the mackerel puree, enhancing water retention and sensory qualities. These findings suggested that TP treatment has potential for preserving mackerel puree during refrigeration.

Gut Microbiota Mediate the Neuroprotective Effect of Oolong Tea Polyphenols in Cognitive Impairment Induced by Circadian Rhythm Disorder.

Oolong tea polyphenols (OTP) have attracted wide attention due to their ability to reduce inflammatory response, regulate gut microbiota, and improve cognitive function. However, exactly how the gut microbiota modulates nervous system activity is still an open question. We previously expounded that supplementing with OTP alleviated neuroinflammation in circadian rhythm disorder (CRD) mice. Here, we showed that OTP can relieve microglia activation by reducing harmful microbial metabolites lipopolysaccharide (LPS) that alleviate CRD-induced cognitive decline. Mechanistically, OTP suppressed the inflammation response by regulating the gut microbiota composition, including upregulating the relative abundance of Muribaculaceae and Clostridia_UCG-014 and downregulating Desulfovibrio, promoting the production of short-chain fatty acids (SCFAs). Moreover, the use of OTP alleviated intestinal barrier damage and decreased the LPS transport to the serum. These results further inhibited the activation of microglia, thus alleviating cognitive impairment by inhibiting neuroinflammation, neuron damage, and neurotoxicity metabolite glutamate elevation. Meanwhile, OTP upregulated the expression of synaptic plasticity-related protein postsynaptic density protein 95 (PSD-95) and synaptophysin (SYN) by elevating the brain-derived neurotrophic factor (BDNF) level. Taken together, our findings suggest that the OTP has the potential to prevent CRD-induced cognition decline by modulating gut microbiota and microbial metabolites.

Impact of Storage Temperature on Green Tea Quality: Insights from Sensory Analysis and Chemical Composition

This study investigated the impact of storage temperatures (−20 °C, room temperature, and 40 °C) on the sensory evaluation, metabolites, and volatile compounds of green tea stored for 12 months. The sensory evaluation revealed that tea samples stored at −20 °C retained their emerald green colour, tender aroma, and refreshing taste. Green tea biochemical constituents, including water extracts and total free amino acids, were measured by Chinese National Standard Methods (GB/T 8305-2013 and GB/T 8314-2013). Tea polyphenols and flavonoids were determined using spectrophotometric methods, while phytochemicals were detected using validated HPLC, and volatile compounds were detected using validated gas chromatography coupled with triple quadrupole mass spectrometry. The analysis showed that tea polyphenols were highest at −20 °C, and flavonoids were significantly reduced at higher temperatures. A similar trend was observed for amino acids, soluble sugar content, and water extracts. Tea catechins, including (-)-epigallocatechin-3-gallate (EGCG) and (-)-gallocatechin gallate (GCG), were highest at −20 °C, showing their susceptibility to temperature. A volatile compound analysis revealed distinct profiles with variations in the abundance of compounds, such as di-methyl sulfide, phenyl ethyl alcohol, indole, and benzaldehyde. This study identifies temperature-sensitive compounds, providing insights into the mechanisms underlying tea quality deterioration during storage.