Strategies for studying in vivo biochemical formation pathways and multilevel distributions of quality or function-related specialized metabolites in tea (Camellia sinensis)

Promising mass spectrometry imaging: exploring microscale insights in food

This review focused on mass spectrometry imaging (MSI), a powerful tool in food analysis, covering its ion source schemes and procedures and their applications in food quality, safety, and nutrition to provide detailed insights into these aspects. The review presented a detailed introduction to both commonly used and emerging ionization sources, including nanoparticle laser desorption/ionization (NPs-LDI), air flow-assisted ionization (AFAI), desorption ionization with through-hole alumina membrane (DIUTHAME), plasma-assisted laser desorption ionization (PALDI), and low-temperature plasma (LTP). In the MSI process, particular emphasis was placed on quantitative MSI (QMSI) and super-resolution algorithms. These two aspects synergistically enhanced MSI's analytical capabilities: QMSI enabled accurate relative and absolute quantification, providing reliable data for composition analysis, while super-resolution algorithms improved molecular spatial imaging resolution, facilitating biomarker and trace substance detection. MSI outperformed conventional methods in comprehensively exploring food functional factors, biomarker discovery, and monitoring processing/storage effects by discerning molecular species and their spatial distributions. However, challenges such as immature techniques, complex data processing, non-standardized instruments, and high costs existed. Future trends in instrument enhancement, multispectral integration, and data analysis improvement were expected to deepen our understanding of food chemistry and safety, highlighting MSI's revolutionary potential in food analysis and research.

Study on dynamic alterations of volatile organic compounds reveals aroma development over enzymatic-catalyzed process of Tieguanyin oolong tea production

To elucidate the formation of characteristic aroma over enzymatic-catalyzed processes (ECP), GC-MS-based volatile-metabolomic combined with desorption-electrospray-ionization coupled mass-spectrometry-imaging (DESI-MSI) were employed to analyze the changes of volatile organic compounds (VOCs) in Tieguanyin tea. A total of 579 VOCs were obtained, from which 24 components involved in five pathways were identified as biomarkers. Among these, four VOCs including 2-furancarboxylic acid, 4-methylbenzaldehyde, N-benzylformamide, cuminaldehyde, were detected in both DESI-MSI and GC-MS analysis, exhibiting dynamic changes along processing steps. RNA-sequencing analysis indicated the genes referring to stress response were activated during tea processing, facilitating the accumulation of flora-fruity aroma in tea leaf. Metabolic pathways analysis revealed that the increase in floral-fruity related components such as volatile terpenoids, phenylpropanoids/benzenoids, indole, alongside a decrease in green leaf volatiles including (E)-2-Hexenal, (Z)-3-Hexenol, played a crucial role in development of characteristic aroma, which could be a feasible index for evaluating processing techniques or quality of oolong tea.

Enhancing the quality of fermented plant leaves: the role of metabolite signatures and associated fungi

Fungi play a pivotal role in fermentation processes, influencing the breakdown and transformation of metabolites. However, studies focusing on the effects of fungal-metabolite correlations on leaf fermentation quality enhancement are limited. This study investigated specific metabolites and fungi associated with high- and low-quality fermented plant leaves. Their changes were monitored over fermentation periods of 0, 8, 16, and 24 days. The results indicated that organoheterocyclic compounds, lipids, lipid-like molecules, organic nitrogen compounds, phenylpropanoids, and polyketides were predominant in high-quality samples. The fungi Saccharomyces (14.8%) and Thermoascus (4.6%) were predominantly found in these samples. These markers exhibited significant changes during the 24-day fermentation period. The critical influence of fungal community equilibrium was demonstrated by interspecies interactions (e.g., between Saccharomyces and Eurotium). A co-occurrence network analysis identified Saccharomyces as the primary contributor to high-quality samples. These markers collectively enhance the quality and sensory characteristics of the final product.

In-depth potential mechanism of combined demulsification pretreatments (isopropanol ultrasonic pretreatments and Ca2+ flow additions) during aqueous enzymatic extractions of Camellia oils

Emulsification is the practical limitation of aqueous enzymatic extractions of Camellia oils. This study aimed to investigate the influence and demulsification mechanisms of isopropanol ultrasonic pretreatments and Ca²⁺ additions on aqueous enzymatic extractions of Camellia oils. Combining isopropanol ultrasonic pretreatments with Ca²⁺ flow additions obtained the highest free oil recovery (78.03 %) and lowest emulsion content (1.5 %). Results indicated that the superior demulsification performance originated from the decrease in emulsion stabilities and formations. First, demulsification pretreatments reduced the oil (14.69 %) and solid (13.21 %) fractions in emulsions to decrease the stability of as-formed emulsions. Meanwhile, isopropanol ultrasonic pretreatments extracted tea saponins (0.38 mg/mL) and polysaccharides (0.23 mg/mL), while Ca²⁺ combined with protein isolates (5.82 mg/mL), tea saponins (7.48 mg/mL) and polysaccharides (0.78 mg/mL) to form precipitates and reduce emulsion formation. This work could promote the practical application of aqueous enzymatic extractions of Camellia oils and enlighten the rise of advanced demulsification pretreatments.

Chromatographic Determination of the Mycotoxin Patulin in 219 Chinese Tea Samples and Implications for Human Health

Patulin (PAT) is a mycotoxin, with several acute, chronic, and cellular level toxic effects, produced by various fungi. A limit for PAT in food of has been set by authorities to guarantee food safety. Research on PAT in tea has been very limited although tea is the second largest beverage in the world. In this paper, HPLC−DAD and GC−MS methods for analysis of PAT in different tea products, such as non-fermented (green tea), partially fermented (oolong tea, white tea, yellow tea), completely fermented (black tea), and post-fermented (dark tea and Pu-erh tea) teas were developed. The methods showed good selectivity with regard to tea pigments and 5-hydroxymethylfurfural (5-HMF) and a recovery of 90–102% for PAT at a 10–100 ppb spiking level. Limit of detection (LOD) and limit of quantification (LOQ) in tea were 1.5 ng/g and 5.0 ng/g for HPLC−UV, and 0.25 ng/g and 0.83 ng/g for GC−MS. HPLC was simpler and more robust, while GC−MS showed higher sensitivity and selectivity. GC−MS was used to validate the HPLC−UV method and prove its accuracy. The PAT content of 219 Chinese tea samples was investigated. Most tea samples contained less than 10 ng/g, ten more than 10 ng/g and two more than 50 ng/g. The results imply that tea products in China are safe with regard to their PAT content. Even an extreme daily consumption of 25 g of the tea with the highest PAT content (124 ng/g), translates to an intake of only 3 μg/person/day, which is still an order of magnitude below the maximum allowed daily intake of 30 µg for an adult.

Pan-transcriptome assembly combined with multiple association analysis provides new insights into the regulatory network of specialized metabolites in the tea plant Camellia sinensis

Specialized metabolites not only play important roles in biotic and abiotic stress adaptation of tea plants (Camellia sinensis (L.) O. Kuntze) but also contribute to the unique flavor of tea, the most important nonalcoholic beverage. However, the molecular networks and major genes that regulate specialized metabolites in tea plants are not well understood. Here, we constructed a population-level pan-transcriptome of the tea plant leaf using second-leaf transcriptome data from 134 accessions to investigate global expression differences in the population, expression presence or absence variations (ePAVs), and differentially expressed genes (DEGs) between pure Camellia sinensis var. assamica (CSA) and pure Camellia sinensis var. sinensis (CSS) accessions. Next, we used a genome-wide association study, a quantitative trait transcript study, and a transcriptome-wide association study to integrate genotypes, accumulation levels of specialized metabolites, and expression levels of pan-transcriptome genes to identify candidate regulatory genes for flavor-related metabolites and to construct a regulatory network for specialized metabolites in tea plants. The pan-transcriptome contains 30 482 expressed genes, 4940 and 5506 of which were newly annotated from a de novo transcriptome assembly without a reference and a genome reference-based assembly, respectively. DEGs and ePAVs indicated that CSA and CSS were clearly differentiated at the population transcriptome level, and they were closely related to abiotic tolerance and secondary metabolite synthesis phenotypes of CSA and CSS based on gene annotations. The regulatory network contained 212 specialized metabolites, 3843 candidate genes, and 3407 eQTLs, highlighting many pleiotropic candidate genes, candidate gene-rich eQTLs, and potential regulators of specialized metabolites. These included important transcription factors in the AP2/ERF-ERF, MYB, WD40, and bHLH families. CsTGY14G0001296, an ortholog of AtANS, appeared to be directly related to variation in proanthocyanins in the tea plant population, and the CsTGY11G0002074 gene encoding F3'5'H was found to contribute to the biased distribution of catechins between pure CSAs and pure CSSs. Together, these results provide a new understanding of the metabolite diversity in tea plants and offer new insights for more effective breeding of better-flavored tea varieties.

Updates on the chemistry, processing characteristics, and utilization of tea flavonoids in last two decades (2001-2021)

Tea flavonoids are widely recognized as critical flavor contributors and crucial health-promoting bioactive compounds, and have long been the focus of research worldwide in food science. The aim of this review paper is to summarize the major progress in tea flavonoid chemistry, their dynamics of constituents and concentrations during tea processing as well as storage, and their health functions studied between 2001 and 2021. Moreover, the utilization of tea flavonoids in the human body has also been discussed for a detailed understanding of their uptake, metabolism, and interaction with the gut microbiota. Many novel tea flavonoids have been identified, including novel A- and B-ring substituted flavan-3-ol derivatives, condensed and oxidized flavan-3-ol derivatives, and glycosylated and methylated flavonoids, and are found to be closely associated with the characteristic color, flavor, and health benefits of tea. Flavoalkaloids exist widely in various teas, particularly 8-C N-ethyl-2-pyrrolidinone-substituted flavan-3-ols. Tea flavonoids behave significantly difference in constituents and concentrations depending on tea cultivars, plantation conditions, multiple stresses, the tea-specified manufacturing steps, and even the long-term storage period. Tea flavonoids exhibit multiple health-promoting effects, particularly their anti-inflammatory in alleviating metabolic syndromes. Interaction of tea flavonoids with the gut microbiota plays vital roles in their health function.

Feasible strategies for studying the involvement of DNA methylation and histone acetylation in the stress-induced formation of quality-related metabolites in tea (Camellia sinensis)

Tea plants are subjected to multiple stresses during growth, development, and postharvest processing, which affects levels of secondary metabolites in leaves and influences tea functional properties and quality. Most studies on secondary metabolism in tea have focused on gene, protein, and metabolite levels, whereas upstream regulatory mechanisms remain unclear. In this review, we exemplify DNA methylation and histone acetylation, summarize the important regulatory effects that epigenetic modifications have on plant secondary metabolism, and discuss feasible research strategies to elucidate the underlying specific epigenetic mechanisms of secondary metabolism regulation in tea. This information will help researchers investigate the epigenetic regulation of secondary metabolism in tea, providing key epigenetic data that can be used for future tea genetic breeding.

Potential mechanisms of the anti-hypertensive effects of RVPSL on spontaneously hypertensive rats using non-targeted serum metabolomics

The study aimed to investigate potential mechanisms for the anti-hypertensive effects of RVPSL on spontaneously hypertensive rats (SHRs) using a non-targeted metabonomic approach. In this study, UPLC/MS-based non-targeted metabolomics was performed to discover metabolite variation of serum in SHRs with RVPSL treatment. As a result, the serum metabolites of SHRs that were administered RVPSL for four weeks exhibited distinct alterations. Nine potential biomarkers, i.e., choline, adenosine, adrenic acid, L-tryptophan, niacinamide, glycocholic acid, propiolic acid, D-glyceraldehyde 3-phosphate, and phosphoglycolic acid, were significantly altered, which were mainly involved in lipid metabolism, vitamin and amino acid metabolism, purine metabolism, the MAPK signaling pathway, and the renin-angiotensin system. This study suggested that RVPSL potentially exerted potent effects of alleviating hypertension in the SHRs mainly via integrated regulations of metabolism and production of choline, L-tryptophan, nicotinamide, and adenosine.

COVID-19 and male reproductive system: pathogenic features and possible mechanisms

Multiorgan dysfunction is the main characteristic of severe COVID-19 patients and the involvement of male reproductive system may occur among these patients. Although there is a limited evidence to confirm the orchitis and virus presence in the semen of patients, there are concerns about the transmission of virus through the semen. In addition, reduced fertility or infertility can be seen as consequences of severe COVID-19 in recovered subjects. In this study, we aimed to review articles related to COVID-19 and male reproductive system to find the possible underlying mechanisms of SARS-CoV-2 in affecting male fertility. The following keywords of SARS-CoV-2, COVID-19, testis, orchitis, semen, angiotensin-converting enzyme 2 (ACE2), hypothalamic-pituitary-testicular (HPT) axis, Hypothalamus, etc., were defined to find the related publications from standard search engines, e.g., PUBMED, SCOPUS, Google Scholar. According to studies, COVID-19 occurs in severe patients as respiratory disease, along with multi-organ failure. The most important mechanisms are classified as direct and indirect pathogenesis of SARS-CoV-2. The presence of ACE2 on the cell surface of various cells in testis increases the risk of direct infection by this virus. SARS-CoV-2 also affects the testis through the cytokine storm. In addition, the important role of HPT axis dysregulation through impaired Leydig cells and hypothalamus should be considered. Using antiviral and immunomodulatory therapy can be harmful for testis function. Further investigations are required to investigate potential mechanisms of male infertility in survivals of COVID-19. Since involvement of testis is essential for fertility, increasing the knowledge of health system may improve the outcomes.

How does tea (Camellia sinensis) produce specialized metabolites which determine its unique quality and function: a review

Tea (Camellia sinensis) is both a plant and a foodstuff. Many bioactive compounds, which are present in the final tea product and related to its quality or functional properties, are produced during the tea manufacturing process. However, the characteristic secondary metabolites, which give tea its unique qualities and are beneficial to human health, are produced mainly in the leaves during the process of plant growth. Therefore, it is important to understand how tea leaves produce these specialized metabolites. In this review, we first compare the common metabolites and specialized metabolites in tea, coffee, cocoa, and grape and discuss the occurrence of characteristic secondary metabolites in tea. Progress in research into the formation of these characteristic secondary metabolites in tea is summarized, including establishing a biological database and genetic transformation system, and the biosynthesis of characteristic secondary metabolites. Finally, speculation on future research into the characteristic secondary metabolites of tea is provided from the viewpoints of the origin, resources, cultivation, and processing of tea. This review provides an important reference for future research on the specialized metabolites of tea in terms of its characteristics.

Translating bioactive peptides for COVID-19 therapy

COVID-19 (Coronavirus disease 2019) is a global pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a positive-sense RNA virus. This virus has emerged as a threat to global health, social stability, and the global economy. This pandemic continues to cause rampant mortality worldwide with the dire urgency to develop novel therapeutic agents. To meet this task, this article discusses advances in the research and potential application of bioactive peptides for possible mitigation of infection by SARS-CoV-2. Growing insight into the molecular biology of SARS-CoV-2 has revealed potential druggable targets for bioactive peptides. Bioactive peptides with unique amino acid sequences can mitigate such targets including, type II transmembrane serine proteases (TMPRSS2) inhibition, furin cleavage, and renin-angiotensin-aldosterone system (RAAS) members. Based on current evidence and structure-function analysis, multiple bioactive peptides present potency to neutralize the virus. To date, no SARS-CoV-2-explicit drug has been reported, but we here introduce bioactive peptides in the perspective of their potential activity against SARS-CoV-2 infection.

Uncovering reasons for differential accumulation of linalool in tea cultivars with different leaf area

It is generally proposed that tea cultivars with larger leaves contain more linalool, an important tea aroma contributor, than ones with smaller leaves. The objective of this study was to confirm the trait and explore the involved reason. Investigation on ten tea cultivars with different leaf areas demonstrated a significant positive correlation between linalool content and leaf area (R² = 0.739, p = 0.010). Analysis of metabolite and gene expression level showed that the transform ability of linalool into linalool oxides was the key factor. Feeding experiments that supplied tea leaves of different leaf areas with [²H₃]linalool under different light conditions revealed that the larger tea leaves receive more light and are less capable of transformation of linalool to linalool oxides, thus leading to linalool accumulation. This information will advance understanding of the variation of linalool content in tea varieties and will provide assistance in breeding and screening of high-linalool tea cultivars.