Oolong Research Articles

Tea Quality: An Overview of the Analytical Methods and Sensory Analyses Used in the Most Recent Studies

Tea, one of the world’s most consumed beverages, has a rich variety of sensory qualities such as appearance, aroma, mouthfeel and flavor. This review paper summarizes the chemical and volatile compositions and sensory qualities of different tea infusions including black, green, oolong, dark, yellow, and white teas based on published data over the past 4 years (between 2021 and 2024), largely focusing on the methodologies. This review highlights the relationships among the different processing methods of tea and their resulting chemical and sensory profiles. Environmental and handling factors during processing, such as fermentation, roasting, and drying are known to play pivotal roles in shaping the unique flavors and aromas of different types of tea, each containing a wide variety of compounds enhancing specific sensory characteristics like umami, astringency, sweetness, and fruity or floral notes, which may correlate with certain groups of chemical compositions. The integration of advanced analytical methods, such as high-performance liquid chromatography (HPLC) and gas chromatography–mass spectrometry (GC–MS), with traditional sensory analysis techniques was found to be essential in the evaluation of the chemical composition and sensory attributes of teas. Additionally, emerging approaches like near-infrared spectroscopy (NIRS) and electronic sensory methods show potential in modern tea evaluation. The complexity of tea sensory characteristics necessitates the development of combined approaches using both analytical methods and human sensory analysis for a comprehensive and better understanding of tea quality.

The tea cultivar ‘Chungui’ with jasmine-like aroma: From genome and epigenome to quality

‘Chungui’ is a newly promoted tea cultivar in China, renowned for producing oolong tea with a distinctive jasmine-like aroma. However, the genetic basis of this unique aroma remains unclear. In this study, the ‘Chungui’ genome, one of the most complete and well-annotated tea genomes, was assembled using PacBio HiFi reads and Hi-C sequencing. Through comparative analysis with typical jasmine flower volatiles, eight core compounds responsible for this aroma were identified. Further research revealed that the jasmine-like aroma in ‘Chungui’ is regulated by a coordinated mechanism involving a significant increase in chromatin accessibility and the demethylation of CHH and CHG in the promoter regions of key aroma-related genes during oolong tea processing. The study proposes that the formation of this unique aroma is driven by the synergistic effect of enhanced chromatin accessibility and reduced methylation, which together lead to the robust upregulation of genes involved in the biosynthesis of these core aroma components. These results provide a molecular foundation for understanding the unique jasmine-like aroma of ‘Chungui’ tea and sets the stage for future studies to explore the roles of these regulatory mechanisms in aroma formation.

Innovative fluorescent ratiometric probe from Oolong tea dreg for highly sensitive bilirubin detection

Bilirubin, a crucial component in heme degradation, is formed during the breakdown of red blood cells in the liver and spleen. Elevated bilirubin levels are closely associated with jaundice and serve as markers for various blood and liver-related disorders. Detection of BR has been approached through various methods with fluorescent methods gaining prominence due to their exceptional sensitivity, rapid response, and precision. Among the fluorescence methods, carbon dots have emerged as versatile optical probes, known for their unique optical properties, low toxicity, and ease of synthesis. However, carbon dots typically exhibit a single emission peak, limiting accuracy due to vulnerability to external interferences. To overcome this limitation, probes featuring multiple independent emission signals are preferred. Chlorophyll, abundant in nature and sourced from biomass, is recognized for its safe and fluorescent properties, making it a secure choice for fluorescence-based sensing. This study introduces an innovative approach utilizing Oolong tea dreg as a source of chlorophyll for creating a fluorescent probe to detect bilirubin. Chlorophyll was partially converted into carbon dots using a combination of extraction and hydrothermal techniques, producing a ratiometric probe with two emission signals. The fluorescence of the probe was quenched in the presence of the bilirubin through the inner filter effect. The proposed probe exhibited outstanding selectivity and a low limit of detection (0.8 µM) for bilirubin. Furthermore, the probe demonstrated satisfactory recovery rates when tested with artificial urine and human urine samples.

Influence of varied processing methods on the antioxidant capacity, antibacterial activity, and bioavailability of Iranian black, oolong, and green leafy teas

In this study, the impact of various tea preparation techniques on the content of bioactive compounds, antioxidant capacity, antibacterial properties, and polyphenol bioavailability in green, black, and oolong tea infusions was examined. The findings demonstrated that the fermentation process significantly influences the levels of bioactive compounds, with green tea infusions exhibiting the highest, and black tea the lowest, content of phenolic compounds. A positive correlation was observed between the content of the phenolic compound and both antioxidant and antibacterial activities. Additionally, the microwave brewing method was identified as the most effective preparation technique for maximizing the bioactive compound content and bioavailability. The inclusion of skim milk powder was found to further enhance the bioavailability of phenolic compounds during digestive process. The research suggests that green tea infusions prepared using the microwave brewing method and supplemented with the skim milk powder, could serve as a functional beverage offering enhanced health benefits.

Processing of oolong tea from passion fruit buds of Passiflora edulis

The research aimed to create oolong tea products from passion fruit buds, diversifying this product line and improving the usage value of this bioactive material. The tea fermentation process was conducted at a temperature of 25 ± 2°C for 4 h, while the semi-drying and final-drying were performed at 50 ± 2°C for 4 h and 90 ± 2°C for 4 h, respectively. Tea product had a moisture content of 5.45%, a reducing sugar content of 1.21 mg/g, and a total polyphenol content of 22.38 mg/g. Tea was brewed at a tea to water ratio of 2.5% for 3 min at 95°C. In sensory evaluations of the brewed tea, color scored 4.93, clarity scored 3.91, smell scored 4.81, and taste scored 4.89. Thus, the product was graded as “good” according to TCVN 12713:2019.

Development of analytical “aroma wheels” for Oolong tea infusions (Shuixian and Rougui) and prediction of dynamic aroma release and colour changes during “Chinese tea ceremony” with machine learning

The flavour of tea as a worldwide popular beverage has been studied extensively. This study aimed to apply established flavour analysis techniques (GC–MS, GC-O-MS and APCI-MS/MS) in innovative ways to characterise the flavour profile of oolong tea infusions for two types of oolong tea (type A- Shuixian, type B- Rougui). GC–MS identified 48 aroma compounds, with type B having a higher abundance of most compounds. GC-O-MS analysis determined the noticeable aroma difference based on 20 key aroma compounds, facilitating the creation of an analytical “Aroma Wheel” with 8 key odour descriptors. APCI-MS/MS assessed real-time aroma release during successive brews linked with the “Chinese tea ceremony” (Gongfu Cha). Multivariate Polynomial Regression (MPR) and Long Short-Term Memory (LSTM) network approaches were applied to aroma and colour data from seven successive brews. The results revealed a progressive decline in both colour and aroma with seven repeated brews, particularly notable after the fourth brew.

Design of a Portable Spectrophotometer Based on Raspberry Pi for Tea Type Classification Using Machine Learning

Abstract The use of spectrophotometers in food and beverage quality analysis has become common. However, portability and high cost have long been a problem for food industry players and small-scale laboratories. In this study, a more compact and low-cost spectrophotometer has been developed using raspberry pi. To validate its performance, the prototype was used to classify green tea, black tea, and oolong tea types. The research started with designing and assembling the hardware using a raspberry pi camera with Complementary Metal Oxide Semiconductor (CMOS) sensor, Digital Versatile Disk (DVD) as diffraction grating, white LED as light source and 3D printer as casing. The prototype was then used to acquire data from green tea, black tea and oolong tea solutions. In the tea type identification process, Principal Component Analysis (PCA) was applied to the data obtained. The experiment involved 30 solution samples of each of the three types of tea. The light source was directed past the sample towards the slit and DVD, then the spectrum image of the light source was displayed through a user interface built using python programming. This research resulted in a spectrophotometer with dimensions of 260 mm x 120 mm x 63 mm that is capable of capturing light spectra in the range of 400 - 700 nm. Based on the experimental results, the classification accuracy of the three types of tea using CNN and Decision Tree reached 100%.

Teh Hitam Cammelia Sinensis Dan Manfaatnya Untuk Kesehatan Pendekatan Berbasis Sains Dan Nilai Islam

Black tea from Camellia sinensis has been a highly popular beverage in Indonesia since the 17th century. Various types of Camellia sinensis tea include white tea, green tea, oolong tea, and black tea. Each type of tea has a distinct antioxidant profile, with black tea containing the highest caffeine content. All types of tea are rich in antioxidants like polyphenols, which play a crucial role in protecting the body from free radicals and reducing the risk of various diseases such as Alzheimer's, diabetes, stroke, hypertension, obesity, cancer, and have antibacterial properties while also serving as an anti-aging treatment for the skin.From an Islamic perspective, the Quran contains numerous verses that command humans to observe and study Allah's creations. This underscores the belief that nothing Allah has created is without purpose, implying that every creation has significant benefits. The consumption of black tea aligns with the principle of maintaining physical health as a form of spiritual responsibility, as also instructed in the Quran. The integration of scientific approaches with religious values elevates black tea beyond merely a beverage enjoyed for its taste, tradition, and health benefits, making it a part of a holistic healthy lifestyle. Utilizing tea production technology and advancing research to uncover the benefits of black tea is a way of expressing gratitude and is considered an act of worship, as its development adheres to the principle of benefiting others.

Evaluating Brand Awareness of Tea Brand with the Case of Moc Suong Oolong Tea Brand Vietnam

Evaluating Brand Awareness of Tea Brand with the Case of Moc Suong Oolong Tea Brand Vietnam

Alginate Spheres: Influence of Agar and Xanthan Gum Incorporation on Membrane Stability and Permeability

Calcium alginate spheres with a volume of about 5 mL can be used for important purposes. Those that incorporate oolong tea give, in addition to the recreational aspect, the possibility of drinking small quantities of this tea, because oolong tea can be used as a compound with antioxidant properties. This incorporation can be achieved by reverse spherification (5 mL). Six types of spheres have been made, all of them with calcium alginate and the presence or absence of agar-agar and xanthan gum—XG—in two concentrations. The weight loss of the spheres, the release of bioactive compounds over time (a total of 48 h), the surface (internal and external) of the membranes, and the physical characteristics of these membranes have been analyzed. The data obtained indicate that the presence of XG prevents the formation of precipitates inside the spheres and slows down weight loss. It also provides opacity to the spheres. However, the incorporation of agar-agar does not have a significant influence on the different parameters analyzed. The release of catechins reaches a maximum of 80% of what could be achieved under ideal conditions, and it reaches 90% in the first 3 h. The incorporation of XG increases the shelf life of the spheres, slows down the release of chelate, and decreases weight loss over time, allowing for a new perspective on the spherification process.

The impact of freeze-dried Baiyedancong-Oolong tea aqueous extract containing bioactive compounds on the activities of CYP450 enzymes, the transport capabilities of P-gp and OATs, and transcription levels in mice.

In this study, (-)-epigallocatechin gallate (EGCG) and caffeine extracted from freeze-dried autumn Baiyedancong Oolong tea (FBOT) were orally administered to mice for 7 consecutive days to explore the effects of BOT and its bioactive compounds on the activities and transcription levels of CYP450 enzymes, intestinal effluence transporter P-gp, and renal ingestion Organic Anion Transporters (OATs). Concurrently, EGCG and caffeine enhanced the activities of CYP3A, CYP2E1, and CYP2C37 in the liver of mice, while impairing the transport capabilities of P-gp and OATs. Reduced levels of MDR1 encoding P-gp transcription in the small intestine and renal OAT1 and OAT3 revealed that transcription was involved in the regulation of CYP450, P-gp, and OATs. The reduced transcription level of liver CYP2E1 suggested that CYP2E1 activity may have been elevated due to alternative mechanisms, but not through transcription. The absorption, metabolism, and excretion of drugs may be influenced by the daily consumption or high-dose administration of BOT and its related products, in which EGCG and caffeine may make great contributions.

Comprehensive investigation on the flavor difference in five types of tea from JMD (Camellia sinensis 'Jinmudan').

Jinmudan (JMD) is a high-aroma variety widely cultivated in China. The current study primarily focuses on the key volatile metabolites in JMD black and oolong teas,and investigates the impact of processing technologies on the aroma quality of JMD tea. However, few studies have explored the suitabilityof JMD for producing a certain type of tea or the characteristic quality differences among various JMD teas using multivariate statistical analysis methods. The principal volatile metabolites contributing to the floral quality of JMD tea are linalool, geraniol, indole and phenethyl alcohol. In JMD black tea (BT), the key volatile metabolites include methyl salicylate, geraniol, (E)-β-ocimene and phenethyl alcohol. In JMD oolong tea (OT), the key volatile metabolites include indole, linalyl valerate and phenethyl alcohol. In JMD yellow tea (YT), the key volatile metabolites include methyl salicylate, geraniol and terpinolene. In JMD white tea (WT), the key volatile metabolites include methyl salicylate, geraniol and terpinolene. In JMD green tea (GT), the key volatile metabolites include (E)-β-ocimene, indole and geraniol. Comparative analysis and KEGG pathway enrichment analysis revealed that flavonoid biosynthesis is the primary metabolic pathway responsible for the taste differences among various tea types. GT exhibited higher levels of phloretin, dihydromyricetin and galangin. The contents of vitexin, tricetin in YT were relatively higher. The contents of aromadendrin and naringenin in BT were higher, while OT contained higher levels of kaempferol. Additionally, WT showed higher contents of 3-O-acetylpinobanksin and 3,5,7-pinobanksin. This study explained the reasons for the quality differences of different JMD tea and provided a reliable theoretical basis for the adaptability of JMD tea. © 2024 Society of Chemical Industry.

Unveiling metabolite network dynamics during Pu-erh tea storage via non-targeted metabolomics

Pu-erh tea's quality and price are inextricably intertwined with age, but false claims about production year can harm both consumers and producers. While tea quality is currently assessed subjectively by experts, developing a scientific method to determine storage time is crucial for the tea industry's growth and integrity. In the present study, analysis of Pu-erh tea (PT) with different storage times showed that the storage process enhanced the complexity of the metabolite networks of extracts and flocs, but the metabolic network characteristics of tea flocs did not exhibit significant changes with the progression of storage time. It is noteworthy that the 41 storage-related core metabolites are important to the storage process; the storage score based on these metabolites was related to the biochemical indicators of the extract and the storage time. Our findings were validated in another independent metabolic data set of green tea (GT), oolong tea (OT), Assam black tea (ABT) and PT. Finally, our regression model based on the storage score could accurately predict the storage time of different teas (R2 = 95.70%). Overall, the findings of our have important guiding significance for expanding the methods for predicting tea storage duration.

Application of scoby bacterial cellulose as hydrocolloids on physicochemical, textural and sensory characteristics of mango jam.

The scoby pellicle of symbiotic culture of bacteria and yeast is a by-product from kombucha fermentation. While a portion is used as starter culture, the remainder is often discarded, yet it can be a valuable source of bacterial cellulose. Scoby from black, green and oolong tea kombucha fermentation was assessed for its hydrocolloid effects in mango jam-making through evaluation of physicochemical, textural and sensory characteristics. Quality of jam was significantly improved with water activity reduction up to 22.22% to 0.679, moisture content reduction up to 37.06% to 19.92%, and a pH drop up to 5.9% to 3.19 with the use of 20 to 100 g kg-1 scoby. In colour analysis, presence of scoby led to a brighter jam due to higher values from 30.98 to a range of 31.82 to 40.83. Texture of jam with scoby gave higher gel strength and adhesiveness, with the most prominent effects from the black tea kombucha. Overall acceptability in sensory test scoring was above 70% on a nine-point hedonic scale with the 40 g kg-1 green tea kombucha scoby jam chosen as the most preferred. Scoby gave significant contributions to jam stability, appearance and texture, showing potential as a clean-label food ingredient. © 2024 Society of Chemical Industry.

Tea Consumption and Human Health: A Review of Benefits and Impact on Chronic Disease Prevention

Tea, derived from the Camellia sinensis plant, is a globally consumed beverage with a rich history spanning thousands of years. Its cultural and social significance is evident in numerous societies, from ancient China to modern Western cultures. Historically revered for its potential health benefits, tea has gained scientific support for its role in chronic disease prevention. This review examines the historical and cultural importance of tea, its bioactive compounds, and its impact on health. Key areas include cancer prevention, cardiovascular health, metabolic syndrome management, and neuroprotection. Green tea, particularly noted for its high concentration of catechins, has been extensively studied for its health-promoting effects, including antioxidant, anti-inflammatory, and cancer-preventive properties. Black, oolong, and white teas each offer distinct benefits due to their unique compositions. Despite the promising evidence, potential risks such as caffeine sensitivity and reduced iron absorption should be considered. Future research is needed to further elucidate the mechanisms underlying tea’s health benefits and to explore its efficacy across diverse populations. Keywords: Tea, Camellia sinensis, Health Benefits, Cancer Prevention, Cardiovascular Health, Metabolic Syndrome.

Development of Spray Drying of Powdered Oolong Tea Incorporated with Chinese Jujube Beverage

One useful economic crop which is utilized worldwide is Chinese jujube. It offers both nutritional and therapeutic benefits. Meanwhile, Oolong tea is a semi-oxidized form of tea which has a flavour that falls somewhere between black tea and green tea. Finally, spray-drying is an important technique used in food preservation. This current study sought to assess the most suitable use of Chinese jujube along with appropriate levels of maltodextrin when creating a mixed Oolong tea which incorporates Chinese jujube and is subsequently processed via spray-drying. Oolong tea served as the control sample, while evaluations were carried out on 60%, 70% and 80% blends of Chinese jujube with maltodextrin which served as a carrier agent at concentrations of 20 g, 30 g, 40 g and 50 g. These solutions underwent spray-drying where the respective inlet and outlet temperatures were 190°C and 80°C. An evaluation of the physico chemical, microbiological and sensory evaluation were performed. There was evidence of an increase in the total phenolic compounds, whereas in contrast there was a decline in antioxidant activity. L* and +a* showed no statistically significant difference, although for +b* a statistically significant difference was found. For products with mixed Chinese jujube and Oolong tea, the moisture, water activity and pH values were shown to be lower, although there was an increase in total soluble solids. In the evaluation, flavour and overall acceptability for Treatment 4 (80% Chinese jujube) achieved the highest respective ratings at 8.17 and 8.13 on the 9-point scale. This demonstrates that spray-drying can be beneficial in the context of powdered particles. The combination of Chinese jujube and powdered Oolong tea provides good antioxidant properties and offers strong potential for applications in the food sector.

Genome-wide epigenetic dynamics of tea leaves under mechanical wounding stress during oolong tea postharvest processing

Understanding the epigenetic responses to mechanical wounding stress during the postharvest processing of oolong tea provides insight into the reprogramming of the tea genome and its impact on tea quality. Here, we characterized the 5mC DNA methylation and chromatin accessibility landscapes of tea leaves subjected to mechanical wounding stress during the postharvest processing of oolong tea. Analysis of the differentially methylated regions and preferentially accessible promoters revealed many overrepresented TF-binding motifs, highlighting sets of TFs that are likely important for the quality of oolong tea. Within these sets, we constructed a chromatin accessibility-mediated gene regulatory network specific to mechanical wounding stress. In combination with the results of the TF-centred yeast one-hybrid assay, we identified potential binding sites of CsMYC2 and constructed a gene regulatory network centred on CsMYC2, clarifying the potential regulatory role of CsMYC2 in the postharvest processing of oolong tea. Interestingly, highly accessible chromatin and hypomethylated cytosine were found to coexist in the promoter region of the indole biosynthesis gene (tryptophan synthase β-subunit, CsTSB) under wounding stress, which indicates that these two important epigenetic regulatory mechanisms are jointly involved in regulating the synthesis of indole during the postharvest processing of oolong tea. These findings improve our understanding of the epigenetic regulatory mechanisms involved in quality formation during the postharvest processing of oolong tea.

Extensive ICP-MS and HPLC-QQQ detections reveal the content characteristics of main metallic elements and polyphenols in the representative commercial tea on the market.

The content of polyphenols and metal elements in tea has an important impact on the choice of consumers. In this study, we conducted a comparative analysis of ten elements including Fe, Mg, Al, Zn, Cu, Mn, Ni, Cr, Pb, and As in 122 representative tea samples from 20 provinces. The results showed that the difference of metal content among six tea categories was greater than that among provinces, and the overall metal content of black tea was relatively higher. The contents of all elements from high to low were: Mg > Mn > Al > Fe > Zn > Cu > Ni > Cr > Pb > As. The contents of Ni, Fe, Al, Zn and Mn showed significant differences among multiple types of tea categories. While the detection rates of Pb and As were 10.7 and 24.6%, respectively. The contents of all elements were in line with the national limit standards. Meanwhile, the relative contents of theanine, caffeine and a total of 53 polyphenolic compounds in 122 tea samples were detected. The analysis showed that the content of these compounds differed least between green and yellow tea, and the largest difference between black tea and oolong tea. This study provides important support for consumers to choose tea rationally.

Insights into “Yin Rhyme”: Analysis of nonvolatile components in Tieguanyin oolong tea during the manufacturing process

Tieguanyin (TGY) is renowned for its distinctive “Yin Rhyme” flavor. To elucidate the underlying formation mechanism, we conducted sensory evaluations, electronic tongue analysis, and widely-targeted metabolomics. Our sensory evaluations and electronic tongue results indicated that TGY exhibits a thick and mellow taste profile, contributing to the “Yin Rhyme” flavor. Metabolomics analysis of tea products revealed that TGY shows significantly higher concentrations of umami substances (L-glutamate, L-theanine) and bitter substances (valine, catechins) compared to Jinguanyin (JGY). Additionally, metabolomic analysis during different oolong tea processing stages revealed significant differences in 21 substances, including L-glutamate, L-theanine, valine, and catechins, between fresh leaves of both varieties. These substances exhibited distinct fluctuation patterns during processing, indicating that the cultivar plays a crucial role in developing the “Yin Rhyme” flavor, which was enhanced throughout processing. This study provides a theoretical foundation for understanding the formation of the unique “Yin Rhyme” flavor of TGY.

Olfactory analysis of oolong tea sensory quality using composite nano-colorimetric sensor array

Chinese oolong tea is famous for its rich and diverse aromas, which is an important indicator for sensor quality evaluation. To accurately and rapidly evaluate sensory quality, a novel colorimetric sensor array (CSA) was developed to detect volatile organic compounds (VOCs) in oolong tea. We further explored the binding mechanism between colorimetric dyes that trigger changes in charge transfer and visible color changes. Based on this, we modified and optimized the CSA to improve the sensitivity by 17.1–234.9% and the stability by 8.7–33.3%. The study also assessed the effectiveness of this method by comparing two linear and two non-linear classification models, with the support vector machine (SVM) model achieving the highest accuracy, identifying different flavor intensity and grades with rates of 100% and 95.83%, respectively. These findings sufficiently demonstrated that the novel CSA, integrated with the SVM model, has promising potential for predicting the sensory quality of oolong tea.