Determination of Theanine and Catechin in Camellia sinensis (Kangra Tea) Leaves by HPTLC and NMR Techniques

Tracing the origin of Taiping Houkui green tea using 1H NMR and HS-SPME-GC-MS chemical fingerprints, data fusion and chemometrics

The narrow geographical traceability of green tea is both important and challenging. This study aimed to establish multi-technology metabolomic and chemometric approaches to finely discriminate the geographic origins of green teas. Taiping Houkui green tea samples were analyzed by headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry and ¹H NMR of polar (D₂O) and non-polar (CDCl₃). Common dimension, low-level and mid-level data fusion approaches were tested to verify if the combination of several analytical sources can improve the classification ability of samples from different origins. In assessments of tea from six origins, the single instrument data test set results in 40.00% to 80.00% accuracy. Data fusion improved single-instrument performance classification with mid-level data fusion to obtain 93.33% accuracy in the test set. These results provide comprehensive metabolomic insights into the origin of TPHK fingerprinting and open up new metabolomic approaches for quality control in the tea industry.

Mechanistic studies on polyphenol rich fractions of Kangra tea by HPTLC and NMR for their antioxidant activities

Abstract

The antioxidant activity in tea is largely driven by its polyphenolic content, however, the antioxidant reaction mechanism and the compounds involved are not well characterized. Therefore, in this study, we performed in-depth profiling of the antioxidant reaction mechanism of Green Tea (GT), Black Tea (BT), and their polyphenolic fractions with free radical using state-of-the-art analytical techniques. The polyphenol enriched fractions from GT and BT were isolated using column chromatography. Catechins were isolated and characterized by diverse spectroscopic techniques. Samples were screened for their antioxidant activity by HPTLC and further evaluated using a spectrophotometer. The free radical reactions with GT, BT, enriched fractions viz, GT Polyphenols (GTP), BT Polyphenols (BTP), and isolated catechins were studied using the ¹³C NMR technique. The highest polyphenol content was found in GTP (795.4 ± 0.012 mg/g) whereas GT (321.0 ± 0.028 mg/g) showed maximum flavonoids content. Individual catechins isolated from GTP were EGCG, ECG, EGC, EC and C. Antioxidant activity followed the order EGCG > ECG > EGC > EC > GTP > C > BTP > GT > BT. In GT, the antioxidant reaction mechanism showed single electron and H-transfer in all catechins, which involved the transformation of the hydroxyl group to the carbonyl group. Whereas in BT theaflavins, conversion of the benzotropolone ring to the six-membered ring was observed.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-021-05297-w.

Metabolite profiling and protein quantification to a large library of 96 horsegram (Macrotyloma uniflorum) germplasm

The present study was framed for the assessment of metabolic diversity of 96 diverse horsegram lines derived from 700 germplasm accessions of Pan India. The nutritional component of horsegram germplasm was studied using nuclear magnetic resonance spectroscopy (¹H NMR) and micro-Kjeldal method. Differential range of protein content was found 13–40% in the selected panel. The related wild species Macrotyloma sar-gharwalensis contained highest protein content (40%), and the lowest protein content (13%) was found in IC-120837 and TCR-1439. Seed based ¹H NMR spectroscopy of horsegram discovered 45 different metabolites (17 amino acids, 7 flavonoids, 10 organic acids/phenolic acids/sugar alcohols/steroids, 7 carbohydrades/sugars, and 4 vitamins). The number of total metabolites quantified among diverse horsegram panel ranged from 25–44. The lowest metabolites number was 26 in PLKU-38, while, IC-280031 and IC-139356 lines showed the presence of highest number of metabolites (44). Lines IC-280031 and IC-139356 were found most nutritive amongst selected panel of horsegram germplasm by containing maximum number of quantifiable metabolites during ¹H NMR spectroscopy study. Further, the NMR based data of 96 germplasms was subjected for statistical analysis (PCA, Matrix plot, stacked charts) that revealed the similarities and variations among the whole germplasm. The methionine, sucrose, maltose, riboflavin and myricetin were observed as differential chemo-markers that help to differentiate the horsegram lines of selected panel. This information will further aid in the selection of nutritionally efficient cultivars for proteomics and genomics studies and these lines can be used as nutraceutical food for the prevention of various health ailments including kidney stone.

Nuclear magnetic resonance-based metabolomics and cytotoxicity (HT-29 and HCT-116 cell lines) studies insight the potential of less utilized parts of Camellia sinensis (Kangra tea)

Camellia sinensis (tea) is an evergreen plant having bioactive compounds associated with various pharmacological effects, including anti-cancerous activity. These phytochemicals are variedly distributed in plant tissues. A detailed study to understand chemical composition within the economically underutilized tea tissues is required to generate value. Therefore, a comprehensive chemical profiling of underutilized C. sinensis parts [coarse leaves, flowers, fruits (immature);n = 9] was performed by NMR techniques. NMR (1D and 2D) spectroscopy ambiguously identified and quantified fifty-seven metabolites (Coarse leaves: 35, flowers; 42, immature fruits; 45). The statistical analysis showed apparent tissue-specific similarities (26 metabolites) and variations. Further, HPLC-DAD revealed absolute quantification of catechins, caffeine and theanine among the different parts of C. sinensis. Moreover, cytotoxicity studies of tea tissues against colorectal cancer cell lines showed anticancer potentials. This chemical information and anticancer activity of underutilized C. sinensis parts will help to develop value added nutraceutical and cosmeceutical products.

Nuclear magnetic resonance-based chemical signature and nutritional discrimination of Macrotyloma uniflorum accessions from the alpine Himalayas

BACKGROUND

Macrotyloma uniflorum (horsegram) is cultivated in the alpine Himalayas for its nutritional benefits. The chemical diversity of M. uniflorum has been explored by several research groups, but none has reported the chemical signature to monitor the identity and quality. To overcome quality control problems and provide more accurate chemotype information, proton nuclear magnetic resonance (¹ H-NMR)-based chemical signature and tentative metabotype discrimination was studied.

RESULTS

Metabolites were identified by characteristic chemical shifts and their correlations in one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) experiments. The identifications were confirmed by reference standards, with in-house databases, and with public databases. From the analysis of seed samples from eight locations, NMR detected 46 diversified metabolites, including 18 amino acids, nine carbohydrates, three vitamins, seven flavonoids, and nine miscellaneous molecules (fatty acids/choline/phenolics/organic acids/sterols). These metabolites generated a single snapshot chemical signature for M. uniflorum. Greater content of identified metabolites was found at high elevations of 1829 m (55.78 g kg^-1 ) followed by 1000-1150 m (19.30-17.23 g kg^-1 ) and 1150-1450 m (7.33-13.41 g kg^-1 ). Principal component analysis of samples revealed that chemotypes grouped into three distinct clusters. 'Cluster-3' was positively correlated with metabolites and found the best nutritionally enriched chemotype.

CONCLUSIONS

A proton nuclear magnetic resonance-based M. uniflorum chemical signature was generated for the first time. The environmental conditions of 1829 m were most suitable for obtaining nutritionally enriched M. uniflorum crops. Overall, this information could help in the conservation, quality control, product development, and agriculture inventions of M. uniflorum. © 2021 Society of Chemical Industry.

1 H-NMR analysis, antioxidant activity, and α-amylase and α-glucosidase inhibitory potential of ten common Thai edible flowers

BACKGROUND

Edible flowers have been used in cooking as foods as well as medicine alternatives. The objectives were to identify a major class of organic compounds in edible flowers by applying proton nuclear magnetic resonance (¹ H-NMR) metabolite fingerprinting and to evaluate bioactivity including antioxidant and α-amylase and α-glucosidase inhibitory activities.

RESULTS

A total of 32 metabolites including five organic acids, eight sugars, 11 amino acids and eight phenolic compounds were identified by using ¹ H-NMR at 600 MHz. The aromatic proton of phenolic compounds was observed at the low-field region ranged between δ 5.5 ppm and 10.0 ppm. Total phenolic content (TPC) of the extracts of edible flowers ranged from 6.0 mg GAE g^-1 dry weight (DW) to 47.97 mg GAE g^-1 DW. Antioxidant activity varied from 140.5 mmol L^-1 TE g^-1 DW to 985.2 mmol L^-1 TE g^-1 DW. The extracts from edible flowers showed dose-dependent inhibition against enzyme. The extract of African marigold (Tagetes erecta L.) had the highest half maximal inhibitory concentration (IC₅₀ ) against α-amylase at 0.13 mg mL^-1 while the extract of flower of Sesban agasta (Sesbania grandiflora Desv.) had the lowest IC₅₀ against α-amylase at 0.63 mg mL^-1 . Moderate correlation was found between IC₅₀ values against α-glucosidase and antioxidant activity values (R²  = 0.66) (P < 0.05).

CONCLUSION

¹ H-NMR application provided metabolomic fingerprinting of edible flowers and the in vitro inhibitory potential activity against key enzymes related to diabetes indicated that specific edible flowers have a potential use for dietary management during the early stages of hyperglycaemia. © 2021 Society of Chemical Industry.

Prickle morphogenesis in rose is coupled with secondary metabolite accumulation and governed by canonical MBW transcriptional complex

Rose is an economically important flowering plant that holds an essential place in cut flower, medicinal, and aromatic industries. The presence of prickles, epidermal outgrowths resembling trichomes, on rose is highly undesirable as these make harvesting and transportation difficult. Attempts were made for generating rose varieties lacking prickles via breeding and natural selections; however, these approaches obtained only chimeric and genetically unstable prickle-less mutants. The alternative way to get rid of prickles is via genetic manipulations, but the molecular mechanisms of prickle initiation and development in rose are almost unexplored. Therefore, the present study was carried out to understand the morphological, molecular, and correlated metabolic changes underlining prickle morphogenesis in a prickle-bearing Rosa hybrida L. cv. "First Red (FR)". The histological and metabolomic analyses at three distinct stages of the prickle morphogenesis, namely, emerging tiny initiating prickles, partially greenish soft prickles, and brownish hard prickles, demonstrated a gradually increasing deposition of phenolic compounds and lignification with development. Corresponding RNAseq analysis revealed an upregulation of the genes involved in secondary metabolism, especially in the phenylpropanoid biosynthetic pathway. A set of genes encoding a transcriptional network similar to the one regulating epidermal cell differentiation leading to phenylpropanoid accumulation and trichome development, was also upregulated. Differential expression of this transcriptional network in prickle-less R. hybrida L. cv. "Himalayan Wonder" compared to prickly FR plants substantiated its involvement in prickle morphogenesis. The results collectively supported the proposition that prickles are evolved from trichomes and provided molecular clues towards engineering prickle-less roses.

SIGNIFICANCE STATEMENT

Prickles, the vasculature less epidermal outgrowths resembling trichomes, are defense organs protecting plants against herbivory. Despite biological significance, the mechanism of prickle morphogenesis remains obscure. Here, we show that like trichomes, prickles accumulate secondary metabolites, especially lignin and flavonoids, during morphogenesis. Cognate transcriptome analysis demonstrated that upregulation of a hormone-regulated transcriptional activation-inhibition network, known to govern trichome morphogenesis, likely triggers the differentiation of epidermal cells to outgrow into prickle.

Validated HPTLC and antioxidant activities for quality control of catechin in a fermented tea (Camellia sinensis var. assamica)

Miang, a Thai traditional fermented tea (Camellia sinensis var. assamica), is exploited as nutraceutical and cosmeceutical ingredients despite limited standardization studies. Thus, this research aimed to develop a simple and rapid method for miang quality control using catechin and high-performance thin-layer chromatography (HPTLC) validated according to the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) and the Association of Official Analytical Collaboration (AOAC). The developing solvent consisting of toluene: ethyl acetate: acetone: formic acid (6:6:6:1 v/v/v/v) showed acceptable specificity with R f value of 0.54 ± 0.02 and linearity with correlation coefficient of 0.9951. The recovery was 98.84%-103.53%, and the RSD of intra- and inter-day precision was 0.70%-3.00% and 1.93%-4.94%, respectively. Miang ethyl acetate fraction is suggested to be attractive ingredient due to rich catechin (25.78 ± 0.53%), prolonged stability at 40 ◦C, and strong antioxidants determined by the assays of ABTS (IC50 = 3.32 ± 0.74 mg/ml), FRAP (89.05 ± 15.49 mg equivalent of FeSO4/g), and inhibition of lipid peroxidation (IC50 = 4.36 ± 0.67 mg/ml).

Multi-omics analysis to visualize the dynamic roles of defense genes in the response of tea plants to gray blight

Gray blight (GB) is one of the most destructive diseases of tea plants, causing considerable damage and productivity losses; however, the dynamic roles of defense genes during pathogen infection remain largely unclear. To explore the numerous molecular interactions associated with GB stress in tea plants, we employed transcriptome, sRNAome and degradome sequencing from 1 to 13 days post-inoculation (dpi) at 3-day intervals. The transcriptomics results showed that differentially expressed genes (DEGs) related to flavonoid synthesis, such as chalcone synthase (CHS) and phenylalanine ammonia-lyase (PAL), were particularly induced at 4 dpi. Consistent with this, the contents of catechins (especially gallocatechin), which are the dominant flavonoids in tea plants, also increased in the leaves of tea plants infected with GB. Combined analysis of the sRNAome and degradome revealed that microRNAs could mediate tea plant immunity by regulating DEG expression at the post-transcriptional level. Co-expression network analysis demonstrated that miR530b-ethylene responsive factor 96 (ERF96) and miRn211-thaumatin-like protein (TLP) play crucial roles in the response to GB. Accordingly, gene-specific antisense oligonucleotide assays suggested that suppressing ERF96 decreased the levels of reactive oxygen species (ROS), whereas suppressing TLP increased the levels of ROS. Furthermore, ERF96 was induced, but TLP was suppressed, in susceptible tea cultivars. Our results collectively demonstrate that ERF96 is a negative regulator and TLP is a positive regulator in the response of tea plants to GB. Taken together, our comprehensive integrated analysis reveals a dynamic regulatory network linked to GB stress in tea plants and provides candidate genes for improvement of tea plants.

Epigenetic targeting of cancer stem cells by polyphenols (cancer stem cells targeting)

Epigenetic alterations are one of the main factors that disrupt the expression of genes and consequently, they have an important role in the carcinogenicity and the progression of different cancers. Cancer stem cells (CSCs) are accountable for the recurrence, metastasis, and therapeutic failure of cancer. The noticeable and specific pathways in CSCs can be organized by epigenetic mechanisms such as DNA methylation, chromatin remodeling, regulatory RNAs, among others. Since epigenetics modifications can be changed and reversed, it is a possible tool for cancer control and treatment. Epigenetic therapies against CSCs are emerging as a very new strategy with a good future expectation to treat cancer patients. Phenolic compounds are a vast group of substances with anticarcinogenic functions, antiinflammatory, and antioxidative activities. It seems these characteristics are related to neutralizing CSCs development, their microenvironment, and metabolism through epigenetic mechanisms. In the current work, the types of epigenetic changes known in these cells are introduced. In addition, some studies about the use of polyphenols acting through a variety of epigenetic mechanisms to counteract these cells will be reviewed. The reported results seem to indicate that the use of these phenolic compounds may be useful for CSCs defeat.

Emerging techniques for determining the quality and safety of tea products: A review

Spectroscopic techniques, electrochemical methods, nanozymes, computer vision, and modified chromatographic techniques are the emerging techniques for determining the quality and safety parameters (e.g., physical, chemical, microbiological, and classified parameters, as well as inorganic and organic contaminants) of tea products (such as fresh tea leaves, commercial tea, tea beverage, tea powder, and tea bakery products) effectively. By simplifying the sample preparation, speeding up the detection process, reducing the interference of other substances contained in the sample, and improving the sensitivity and accuracy of the current standard techniques, the abovementioned emerging techniques achieve rapid, cost-effective, and nondestructive or slightly destructive determination of tea products, with some of them providing real-time detection results. Applying these emerging techniques in the whole industry of tea product processing, right from the picking of fresh tea leaves, fermentation of tea leaves, to the sensory evaluation of commercial tea, as well as developing portable devices for real-time and on-site determination of classified and safety parameters (e.g., the geographical origin, grade, and content of contaminants) will not only eliminate the strong dependence on professionals but also help mechanize the production of tea products, which deserves further research. Conducting a review on the application of spectroscopic techniques, electrochemical methods, nanozymes, computer vision, and modifications of chromatographic techniques for quality and safety determination of tea products may serve as guide for other types of foods and beverages, offering potential techniques for their detection and evaluation, which would promote the development of the food industry.

Comprehensive nutritional profiling and activity directed identification of lead antioxidant, antilithiatic agent from Macrotyloma uniflorum (Lam.) Verdc

Macrotyloma uniflorum (Lam.) Verdc. (family Fabaceae) is traditionally important pulse used for kidney stone degradation, cold,cough, asthma and in bronchial issues. It is well reported for the antilithiatic activity and nutritional profiling but no attempt has been made to find out the mechanism and nutrient responsible for the activity in its seed decoction. Therefore, lead high altitude variety responsible for the highest nutrient content and antilithiatic activity was selected for the study. Boiled spray dried extract (M₁), lead fractionation (Spray dried residual water fraction: M₂), and crude powder extract (M₃) were nutritionally profiled using proximate composition analysis, Atomic absorption spectroscopy (minerals and trace elements), Ion exchange chromatography (carbohydrate analysis) and NMR spectroscopy (polar and non polar metabolite analysis). These extracts were also screened for the antilithiatic activity and found significantly important. M₁ showed more activity than M₃. Further, boiled extract was fractionated with different polarity of solvents (hexane, chloroform, n-butanol, residual water extract). All fractions and reference standard (cystone) were screened for the antilithiatic activity. M₂ showed highest activity followed by ethyl acteate while hexane and chloroform did not show any activity in comparison to standards. Thus, lead fraction and market reference standard (cystone) were validated for the presence of nutritional components. Moreover, the selected nutritional components were individually and in combinations screened for the activity which revealed that kidney stone degradation was due to the synergetic action of components than the individual. The results clearly pave a way that Macrotyloma uniflorum is best for combating with malnutrition and kidney stone related problems.

Concurrent production and relative quantification of vasicinone from in vivo and in vitro plant parts of Malabar nut (Adhatoda vasica Nees)

The present study documents a simultaneous production and comparative assessment of extracted vasicinone from in vivo (leaves and stems) and in vitro (leaves, stems and calli) plant parts of Adhatoda vasica Nees, a well-known medicinal plant. High-performance thin layer chromatography (HPTLC) analysis of the above-mentioned plant parts, collected at their 60-day-old growth stage, was performed via methanolic extraction and with the aid of toluene:butanol:butyl acetate (9:0.5:0.5; v/v/v) solvent system. The method was validated with the help of aluminium sheet precoated with silica gel 60 F₂₅₄ TLC plates, following the ICH guidelines in order to maintain accuracy, precision and repeatability. Correlation coefficient, limit of detection and limit of quantification values were found to be reasonable. The outcome revealed a linearity that ranged between 2 and 6 µg/spot. During the comparison of estimated vasicinone quantity from in vivo and in vitro plant parts, it was evident that in vitro samples produced relatively higher vasicinone than that of the in vivo counterparts. Maximum vasicinone (6.402 ± 0.010% of dry weight) production was quantified from in vitro leaves followed by calli (5.222 ± 0.092% of dry weight) and in vitro stems (2.007 ± 0.041% of dry weight). On the other hand, in vivo leaves and stems produced comparatively lower quantities of vasicinone (2.412 ± 0.139 and 1.933 ± 0.046% of dry weight, respectively) suggesting the in vitro clonal propagation as a superior approach in comparison to in vivo propagation. Nonetheless, simultaneous production from both the sources (in vivo and in vitro plant parts) provides a new avenue for augmented production of vasicinone.

l-Theanine: An astounding sui generis integrant in tea

l-theanine (l-Th), a non-protein amino acid present in tea, is a valuable nutraceutical product with unique health benefits and used as an additive in food industry. l-Th enhances the umami taste but its use is limited due to its inadequate production. Different extraction approaches from tea shoots, chemical synthesis to microbial transformation have been tried to meet its demand. In vitro, in vivo as well as clinical studies have shown its positive effect in regulating CNS disorders. l-Th has become choice ingredient in CNS active products due to its anti-stress and neuroprotective role in dementias particularly in retrogression of Alzheimer's. l-Th biochemically modulates various anti-neoplastic agents by increasing their bioavailability in tumour cells. The review, is an effort to condense the recent research on l-Th highlighting its biological resource, plausible role in tea plant, production approaches, its physiological role on human health and future prospects.

Reliable reference genes for normalization of gene expression data in tea plants (Camellia sinensis) exposed to metal stresses

Tea plants [Camellia sinensis (L.) O. Kuntze] are an important leaf-type crop that are widely used for the production of non-alcoholic beverages in the world. Exposure to excessive amounts of heavy metals adversely affects the quality and yield of tea leaves. To analyze the molecular responses of tea plants to heavy metals, a reliable quantification of gene expression is important and of major importance herein is the normalization of the measured expression levels for the target genes. Ideally, stably expressed reference genes should be evaluated in all experimental systems. In this study, 12 candidate reference genes (i.e., 18S rRNA, Actin, CYP, EF-1α, eIF-4α, GAPDH, MON1, PP2AA3, TBP, TIP41, TUA, and UBC) were cloned from tea plants, and the stability of their expression was examined systematically in 60 samples exposed to diverse heavy metals (i.e., manganese, aluminum, copper, iron, and zinc). Three Excel-based algorithms (geNorm, NormFinder, and BestKeeper) were used to evaluate the expression stability of these genes. PP2AA3 and 18S rRNA were the most stably expressed genes, even though their expression profiles exhibited some variability. Moreover, commonly used reference genes (i.e., GAPDH and TBP) were the least appropriate reference genes for most samples. To further validate the suitability of the analyzed reference genes, the expression level of a phytochelatin synthase gene (i.e., CsPCS1) was determined using the putative reference genes for data normalizations. Our results may be beneficial for future studies involving the quantification of relative gene expression levels in tea plants.