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Catechin, the major ingredient in tea that affects its taste, varies based on the tea variety, climate, and extraction techniques. Although several techniques have been developed to determine catechin levels, an easy-to-use method is still lacking. Herein, the catechin levels were determined using papain for the first time. After incubating papain with catechin, the precipitate was discarded, and the remaining catechin-enzyme complex in the supernatant was determined by UV–visible absorption spectroscopy. Upon catechin binding papain's main absorption band (at 280 nm) was altered, reflecting conformation changes in their aromatic amino acids. It was supported by the kinetic measurements determined with N-α-benzoyl-arginine- p -nitroanilide (BAPNA) as a substrate. Complex formation between catechin and papain markedly affects the enzyme activity, resulting in the diminishes of the yellow-colored product observed at 410 nm in a concentration-dependent manner. Under the optimum conditions, the analytical curve was linear in the concentration range 0.10 – 0.80 mg/mL (r2 = 0.9893) with a detection limit of 0.44 mg/mL. This developed biosensor demonstrated long-term stability (90 days) and reproducibility with a relative standard deviation below 10%. This usefulness of papain's conformation changes was further demonstrated in the analysis of tea infusion samples, and the recoveries are in the acceptable range (79.1–81.2%). • The papain secondary structure was altered based on the interaction with catechin. • The precipitate and the soluble catechin-papain complexes are both observed. • Catechin-papain activities are linearly related to the catechin concentration. • Lower apparent K m and V max observed suggest the uncompetitive inhibition by catechin. [ABSTRACT FROM AUTHOR]

Catechins and theaflavins, as the primary bioactive constituents of black tea, have a significant impact on its color, aroma, and flavor profile. We developed a rapid and precise method using HPLC to detect catechins and theaflavins in black tea. The method employed 0.1% formic acid-acetonitrile (phase A) and 1% formic acid-water (phase B) as mobile phases. Separation occurred on an Agilent SB-C18 column (4.6 mm × 250 mm, 5 µm), with 20 μL injection volume. Detection took place at 30 °C with a flow rate of 1 mL/min for 55 min.Quantitative determination utilized the external standard method, exhibiting high sensitivity (limit of detection: 0.19 to 5.14 μg/mL) and a strong linear correlation (R2 ≥ 0.9993) between concentration range and peak area. Precision, repeatability, and stability were excellent, with relative standard deviations (RSDs) below 5% (n = 5). The average recovery rate of standard addition ranged from 98.02% to 102.57%, with an RSD of less than 3.17% (n = 5). In summary, this straightforward, efficient, and precise approach is well-suited for both qualitative and quantitative analysis of catechins and theaflavins in tea. It overcomes the limitations of previous methods, providing a valuable tool for evaluating the quality and composition of black tea. • A HPLC method has been developed for detection of both catechins and theaflavins. • This method detects 14 Catechins and theaflavins. • The method is a simultaneous, rapid, accurate and efficient approach. • The method was validated by analysis extract of Longgu black tea. [ABSTRACT FROM AUTHOR]

Rapid and accurate assaying catechins, caffeine, bitterness and astringency prediction are integral to quality assessment and control of Pu-erh ripen tea (PRT). The traditional experimental procedures for content quantification and sensory evaluation are time-consuming and lab-dependent, while near-infrared (NIR) technology has the potential to address this issue. In this work, an efficient and environment-friendly approach was established for caffeine and catechins prediction, and bitterness and astringency evaluation of PRT, using a portable NIR spectrometer coupled with chemometrics. A total of 100 PRT samples were collected for analysis and seven different spectral preprocessing methods and two variable selection algorithms were employed to improve the prediction performance of the partial least squares regression (PLSR) model. The optimized models achieved satisfactory results for the prediction of caffeine and catechins (catechin, catechin gallate, gallocatechin, epicatechin gallate, epigallocatechin, and epigallocatechin gallate), as well as bitterness and astringency, with the correlation coefficient of the prediction set (R p) above 0.9, and residual prediction deviation (RPD) over 2.5. This research offers an alternative for portable and rapid quantification of caffeine and eight catechins and evaluation of bitterness and astringency of PRT. • Portable NIR spectroscopy coupled with PLSR was used to establish prediction model. • R p of bitterness and astringency evaluation were above 0.95. • Caffeine and eight individual catechins were predicted in high accuracy. • It provides a rapid and green approach for evaluating Pu-erh ripen tea quality. [ABSTRACT FROM AUTHOR]

The brown marmorated stink bug (BMSB) (Halyomorpha halys Stal) has become a global threat to hazelnut yield and quality in the last decade by establishing a considerable population in hazelnut orchards in some countries. For the first time ever, we conducted an analysis on metabolic response of a necrotic hazelnut kernel, which is one of the most important damage types caused by BMSB feeding. In the present study, we investigated how hazelnut kernels respond to BMSB infestations in terms of the individual phenolics and fatty acid compositions in four different kernel types [i.e., control/healthy kernel (HK) , whole of damaged kernel (WDK), healthy part of damaged kernel (HPDK), necrotic part of damaged kernel (NPDK)]. Individual phenolics were significantly affected by BMSB. Especially, epicatechin and catechin from flavan-3-ols, rutin from flavonol, and caffeic from phenolic acids increased significantly in kernel injured by BMSB. Major fatty acids were significantly affected by BMSB, except for palmitic. Oleic acid decreased in kernel injured by BMSB (WDK, HPDK and NPDK) compared with the HK, while palmitic, stearic, and linoleic acids increased. As from our results, it was revealed that BMSB affected the secondary metabolites in hazelnut and had a remarkable effect on epicatechin, rutin, caffeic acid and p -coumaric acid. • Individual phenolics were significantly affected by BMSB feeding. • Certain flavonoids and phenolics increased significantly in kernel injured by BMSB • Major fatty acids were significantly affected by BMSB feeding, except for palmitic. • Oleic decreased in kernel injured by BMSB compared with the HK. [ABSTRACT FROM AUTHOR]

Highlights • Six traditional Chinese tea types were produced from the same fresh tea leaves. • Dynamic changes of major components in six types of tea produced from the same leaves were analysed. • Six types of tea and fresh leaves could be clearly distinguished based on free amino acid analysis. • Total free amino acids and catechins drastically decreased during fermentation. • GA content significantly increased in all six types of tea compared with the fresh leaves. Abstract The manufacturing process plays a crucial role in influencing tea quality by altering its chemical composition. To investigate the effect of different manufacturing processes on the primary chemical components of tea, six types of traditional Chinese tea were produced from the same batch of fresh tea leaves. Dynamic changes of the major chemical components, including 22 free amino acids, 6 catechins, 2 alkaloids, and gallic acid (GA), in those six types of tea and fresh tea leaves, were analyzed. Principal component analysis (PCA) showed fresh tea leaves and the six tea types processed by different methods could be distinguished based on free amino acid chemometric analysis. The content of total free amino acids and catechins drastically decreased during fermentation, whereas GA content increased significantly. The catechin content varied greatly among different types of tea, indicating that epimerization and oxidative degradation of catechins occurred during tea processing. Caffeine content was relatively stable, whereas theobromine content fluctuated slightly according to the production process of the different teas. This study confirmed the dynamic changes in the primary characteristic metabolites during processing of different teas and demonstrated potential biomarkers to monitor the manufacturing process of different teas. [ABSTRACT FROM AUTHOR]

The applicability of using front-face fluorescence spectroscopy to compare profiles of commercially produced New Zealand Pinot Noir grape juice and wine samples from closely related vineyard sites and different grapevine clones was assessed by monitoring eleven batches of grape juices (different sites and clones) during the commercial winemaking process (pre-fermentation, pre-barrelling, barrelled wines). Deconvolution of the recorded fluorescence excitation-emission matrices was carried out using parallel factor analysis (PARAFAC) and the scores plots thereof showed sample groupings on the basis of clone and indicated chemical differences based on vineyard site, winemaking and barrel properties. The four components revealed by the PARAFAC models had their excitation/emission maxima at 278/360 nm, 260/390 nm, 278/315 nm and 320/415 nm, respectively and were tentatively assigned to multiple fluorophore contributions of tryptophan and hydroxyl benzoic acid derivatives (vineyard site discrimination), caffeic acid (clone discrimination), catechin and tyrosol related fluorophores (winemaking based discrimination). The applied methods after further validation have potential to be used as a rapid way to screen grape juices and wines and to provide winemakers with information on the potential quality of their wine. [ABSTRACT FROM AUTHOR]

In order to clarify the relationship between withering process and green tea quality, dynamic changes in the major chemical components of green tea, including amino acids, catechins, caffeine (CAF) and gallic acid (GA), were investigated during withering at different times (ranging from 0 h to 21 h) and temperatures (15, 20 and 25 °C). One-way and two-way analyses of variance (ANOVA) with Duncan’s test were used to analyse the change of chemical components. Results showed that during the withering process, contents of most free amino acids increased with increasing withering time and temperature. Theanine (Thea) contents decreased slightly with fluctuations, glutamic acid (Glu) and aspartic acid (Asp) contents presented an increase–decrease pattern, whereas proline (Pro) contents remained almost constant. Total free amino acids increased up to 18 h but declined thereafter. Most catechins decreased with increasing withering time and temperature. In addition, GA contents increased with increasing time and temperature; while CAF contents increased with increasing withering time, but were only slightly correlated with withering temperature. This experiment recommended withering for 15–18 h below 25 °C to produce high quality green tea. [ABSTRACT FROM AUTHOR]

Drying is an important process in black tea processing, at the same time, catechin is an important factor in determining the sensory quality of black tea. However, there is a lack of effective real-time detection methods for the detection of catechins in black tea drying process. Therefore, we analyzed the trends of catechins in black tea drying process under different drying conditions and further explored the quantitative prediction model of eight individual catechins in black tea drying process by Least squares support vector machine (LS-SVM) based on near-infrared spectroscopy (NIRS) and chemometrics methods. The results showed that the prediction accuracy of the eight monomeric catechins prediction models established based on the extraction of competitive adaptive reweighted sampling (CARS) and successive projections algorithm (SPA) feature spectra achieved the best results, and the correlation coefficient values of the prediction sets (R p) were all greater than 0.98, and the relative percentage deviation (RPD) values were all greater than 5. The gallocatechin gallate (GCG) with the highest prediction accuracy was 0.9977 and the RPD value was 14.8. This study shows that the method based on near-infrared spectroscopy and chemometrics has strong predictive power for catechins in black tea drying process, which is a guideline for controlling the sensory quality of black tea drying. • Different drying temperatures and times affect the catechin content of black tea. • Catechin during black tea drying was monitored using NIR spectroscopy. • Different quantitative prediction models were compared to accurate detection of catechins. • NIR spectroscopy can be used to monitor the drying process of black tea. [ABSTRACT FROM AUTHOR]

Different from post-fermented teas, pickled tea is a unique processed tea of fresh leaves of Camellia sinensis var. assamica under anaerobic fermentation. It is mainly consumed in ethnic minority areas in southwest China. The chemical characteristics of pickled tea during processing were studied by mass spectrometry-based metabolomics and quantitative determination. Metabolomics results showed that a total of 44 marker compounds, including flavan-3-ols, organic acids, glycosides, and flavonoids were identified in pickled tea during fermentation. Thereinto, galloylated catechins were mainly degraded or oxidated into the corresponding nongalloylated catechins and theaflavins. Caffeine and theobromine slightly varied, while organic acids markedly varied during the whole processing. In addition, butanedioic, lactic, and gallic acid were found as the main organic acids in pickled tea and their contents were 220 ± 9, 177 ± 21, and 172 ± 6 μg/g, respectively. The inhibitory effects of pickled tea samples on α-amylase and α-glucosidase were also investigated and subsequently analyzed with respect to chemical-biological activities correlation. The results showed that glycosides and most organic acids were key α-amylase inhibitors, while catechins and flavonoids were key α-glucosidase inhibitors. The present study aimed to comprehensively explore the chemical variation of pickled tea during processing, and key inhibitors of α-glucosidase and α-amylase. [Display omitted] • The variation of organic acids in pickled tea samples was investigated. • The hypoxic and longtime fermentation was the key process of pickled tea. • Glycosides and most of organic acids were the main α-amylase inhibitors. • Catechins, theaflavins, and flavonoids were the main α-glucosidase inhibitors. • There were two stages of the glycolysis during the pickled tea processing. [ABSTRACT FROM AUTHOR]

A computational tool was developed to facilitate proanthocyanidin analysis using data collected by ultra-high-performance liquid chromatography-diode array detection-high resolution accurate mass-mass spectrometry (UHPLC-DAD-HRAM-MS). Both identification and semi-quantitation of proanthocyanidins can be achieved by the developed computational tool. It can extract proanthocyanidin chromatographic peaks, deconvolute the isotopic patterns of A-type, B-type, and multi-charged proanthocyanidins ions, and predict proanthocyanidin structures. Proanthocyanidins were quantified by an external calibration curve of catechin and molar relative response factors (MRRFs) of proanthocyanidins. Quantitation results including concentrations of total proanthocyanidins, individual proanthocyanidins, and proanthocyanidins with different degrees of polymerization and different types of linkage were calculated by the program and exported into an Excel spreadsheet automatically. The program was applied to the analysis of seven plant materials including apple, cranberry, dark chocolate, grape seed extract, jujube, litchi, and mangosteen. The identification results were compared with the results obtained by manual processing. The program can greatly save the time needed for the data analysis of proanthocyanidins. [ABSTRACT FROM AUTHOR]

A new rapid isocratic HPLC method was developed to quantify xanthine oxidase activity in several dairy products by determining both substrate (xanthine) and product (urate) concentrations at short retention times (6.76 min and 4.92 min, respectively) with high values for linearity and reliability. The impact of added green tea catechins (1000 ppm) on xanthine oxidase activity was also examined in dairy products containing fat globules using the developed HPLC method. The addition of (+)-catechin, (−)-epigallocatechin gallate (EGCG), and green tea extract significantly ( p ≤ 0.05) decreased the xanthine oxidase activity of these products. The effect of EGCG on decreasing xanthine oxidase activity of milk fat globules was stronger than for (+)-catechin, and can be attributed to different structures of green tea polyphenols, such as different numbers of OH groups in catechins. The results of this study suggest possible associations between milk fat globule surfaces and green tea catechins. [ABSTRACT FROM AUTHOR]

Green tea extract (GTE) was incorporated into full-fat cheeses at 250, 500, and 1000 ppm to investigate the effect of green tea catechins on antioxidant properties and microstructure of cheese, and recovery of catechins. Cheeses were ripened for 90 days at 8 °C followed by simulated gastrointestinal digestion. The composition on Day 0, and pH, total phenolic content (TPC), and antioxidant activity (AA) of the cheeses on Days 0, 30, and 90, were determined. The concentrations of the major GTE catechins in the curd and from the digesta of mature cheeses were determined using HPLC. Addition of GTE significantly ( p ≤ 0.05) decreased the pH of whey and curd during cheese manufacture and ripening, however there was no significant ( p > 0.05) effect on moisture, protein, or fat contents. Addition of GTE increased TPC and AA at all concentrations, but in a non-linear manner. Individual catechins were selectively retained in the curd, whereas different portions were recovered from the cheese digesta. Transmission electron microscopy showed that the ripened control cheese had a regular distribution of milk fat globules entrapped in a homogeneous structure of casein proteins, which was disrupted by GTE. Interactions between green-tea catechins and cheese fat were confirmed by Fourier transform infrared spectroscopy. [ABSTRACT FROM AUTHOR]

Although the antioxidant activity of individual phenolic compounds is widely described, there is a lack of information about their interactions and potential synergistic or antagonistic effects. In this study the interaction between resveratrol and other phenolics (gallic acid, caffeic acid, catechin, quercetin) in equimolar binary mixtures was investigated using three different antioxidant assays (FRAP, DPPH, and Briggs–Rauscher reaction). The obtained results indicate that there are differences in the activity of mixture of phenolic compounds and resveratrol depending on mechanism of the used method. The synergistic effect between catechin and resveratrol was confirmed using all three methods. The reducing activity of the mixture of caffeic acid and resveratrol was almost 10.0% higher than the activity of the individual compounds, while in the other two assays that evaluate free radical scavenging activity of the samples, this phenolic mixture showed antagonistic effect. Significantly prolonged inhibition time, and extremely enhanced effect of mixtures of gallic acid and resveratrol and of catechin and resveratrol, by 45.5 and 53.3% respectively, was detected using Briggs–Rauscher reaction. The obtained results support the fact that the antioxidant activity of phenolic mixtures cannot be predicted from the activity of pure compounds, but they could be useful in the explanation of the activity of their mixtures. [ABSTRACT FROM AUTHOR]

• UPLC/MS/MS Chemical profiling of black, green and white tea grades was attempted. • Theasensinin C and E, theaflavin and theacitrin were the main markers of black tea type. • Catechin, epicatechin, epigallocatechin, were the main markers of green tea type. • Theanine, oolongotheanine and were the main chemical markers of white tea type. • Markers up and down-regulated between whole, broken and fanning tea grades determined. In the current study, seven Sri Lankan tea grades; Orange Pekoe, Flowery Pekoe, Broken Orange Pekoe Fannings, Broken Orange Pekoe black tea, green tea, silver tips and golden tips white tea grades were subjected to comprehensive metabolic profiling using UPLC-MS/MS combined with chemometrics. Theasensinin C and E, theaflavin and theacitrin were the main chemical markers of black tea type, catechin, epicatechin, epigallocatechin, methyl epigallocatechin were the main discriminatory markers of green tea type, while theanine, oolongotheanine and quercetin glycosides were the main chemical markers of white tea type. Theogalloflavin, epigallocatechin and flavonoid glycosides were the main down-accumulated metabolites while theaflavin gallate, and N -ethyl pyrrolidinone epicatechin were the chief up- accumulated metabolites between whole and broken black tea leaves grades while puerin A and C and gallic acid were the main down-accumulated metabolites and N -ethyl pyrrolidinone epicatechin gallate was the main up-accumulated one between broken and fanning black tea grades. [ABSTRACT FROM AUTHOR]

• Notable correlations between pellicle colors and phenolics in kernel without pellicle. • Positive correlations between TPCs of three forms in pellicle and their colors. • Dark walnuts with high contents of flavanols, flavones and flavonols in free form. Although walnut kernels are a rich source of phenolic compounds, little is known about the profiles of phenolic compound forms in various colored-pellicle walnuts, which may be important for product development and utilization. In this work, the free, esterified and bound forms of phenolic compounds in various colored-pellicle walnuts were identified using ultra-high-performance liquid chromatography coupled to tandem mass spectrometry ((UHPLC-MS/MS). The total phenolics (TPCs) in pellicle, kernel without pellicle and whole kernel (with pellicle) were presented in the free form (62.6%) and bound form (1.30 %–12.2 %). Positive correlations were found between the TPCs of three forms in pellicle and the pellicle color, with correlation coefficients of 0.920, 0.990 and 0.940. In addition, the phenolic compounds in free form in the whole kernel (with dark pellicle) demonstrated notable advantages in flavanols, flavones and flavonols contents, particularly (+)-catechin (C) (40.7 μg/g) and epicatechin (EC) (25.8g/g), which were 2–153 times higher than other phenolic compounds in free form. Furthermore, the dark group of esterified phenolic acids showed advantages, particularly ellagic acid (428 μg/g) and gallic acid (130 μg/g). [ABSTRACT FROM AUTHOR]

• Five year storage is critical point for components and taste of crude pu-erh tea. • Gallotannins are marker compounds for storage of crude pu-erh tea. • Galloylated catechins are responsible for taste changes of tea infusion. • Flavonol glycosides contribute less to the astringency of crude pu-erh tea infusion. Crude Pu-erh tea (CPET) is distinct from ripened Pu-erh tea, and usually needs a long-term aging under natural conditions, which can make it taste more mellow. In the present study, metabolomics integrated with sensory evaluation was used to investigate the key astringency compounds of CPET during storage. Metabolomics results showed that these CPET samples could be classified into two groups, one was storage from 1 to 5 years, and the other was 6–8 years. Meanwhile, non-galloylated catechins, hydroxycinnamic acids, flavonol glycosides, and gallotannins were marker compounds, which were responsible for distinguishing short and long aging time. Correlation coefficients between astringency scores and (–)-epigallocatechin, (–)-epicatechin, quercetin-glucose, myricetin-glucose, and (–)-gallocatechin gallate were 0.826, 0.821, 0.815, 0.811, and 0.718, respectively. The astringency contribution of galloylated catechins and flavonol glycosides was also investigated by treating CPET infusion with tannase and β-glycosidase. The tannase treatment greatly reduced the contents of galloylated catechins, and correspondingly decreased the astringency scores. β-Glycosidase could hydrolyze the flavonol glycosides into flavonol aglycones, but the astringency intensity of CPET infusion was not affected. These results suggested hydrolysis of galloylated catechins was the key reason for astringency decrease during storage of CPET, while flavonol glycosides comparatively contributed less to the astringency. [ABSTRACT FROM AUTHOR]

• NIR-HSI was used for quality monitoring of fermentation process of black tea. • Qualitative and quantitative models were developed to assess the quality. • Spatial distribution of catechins during fermentation was mapped by HSI. • Noncontact evaluation for intelligent processing of black tea was achieved. Fermentation is the most critical step in black tea processing and contributes to the taste and appearance of black tea. Conventionally, the degree of fermentation is evaluated through sensory reviews by experts. However, this method has low accuracy and is subject to reviewers' experience. In this study, the fermentation quality of black tea was qualitatively and quantitatively evaluated through near-infrared hyperspectral imaging (HSI). The spectral information of samples of four fermentation degrees was collected and preprocessed using standard normal variate. The developed qualitative model could discriminate fermentation degrees, with a correct classification rate of 83.33 % for the prediction set. The quantitative prediction model achieved excellent prediction accuracy for the catechin content, with a residual prediction deviation of 2.18. Finally, the spatial distribution of catechins during fermentation was mapped through chemical imaging. Our study confirmed the feasibility of HSI for monitoring the fermentation quality of black tea. [ABSTRACT FROM AUTHOR]

• Ultrasound irradiation was applied in the model wine containing glutathione. • Xanthylium cation pigments increased after ultrasound treatment. • Glutathione inhibited the pigments formation and ultrasound reduced the effects. • Ultrasound irradiation can be applied in winery to modify wine color properties. Xanthylium cations and its ethyl ester are important pigments derived from (+)-catechin and glyoxylic acid in wine. In this paper, ultrasound treatment was applied in model wine containing glutathione to study its effects on the formation of xanthylium cation pigments triggered by free radicals from the ultrasound cavitation. The changes in color parameters, concentration of pigment compounds and free radicals were investigated during wine storage by the means of ultraviolet visible (UV–vis) spectrophotometer, colorimeter, high performance liquid chromatography with mass spectrometry (HPLC-MS) and electron paramagnetic resonance (EPR), respectively. Results indicate that longer ultrasonic treatment in conjunction with glutathione can significantly enhance the formation of xanthylium cation pigments and accelerate the red wine color evolution, and no extra (+)-catechin was involved, which might be attributed to the stronger 1-hydroxyethyl radicals intensity induced by ultrasound irradiation. In summary, ultrasound treatment can accelerate the oxidative coloration of wine with GSH during ageing, which would contribute to well understand the changing mechanism of wine color properties modified by ultrasound. [ABSTRACT FROM AUTHOR]

• ECG and flavonol di-glycosides accumulate in cultivars of assamica variety. • EGCG and flavonol tri-glycosides accumulate in cultivars of sinensis variety. • Flavonoids can be used as indicators for distinguishing various tea plant resources. • Accumulation pattern of flavonoids mainly depends on tea plant genetic background. Flavonoids are important phenolic compounds in tea plant since they have a large number of physiological functions for plants themselves and human beings. Tea samples (n = 151) harvested from 3 varieties, 9 plantation areas and 107 cultivars were analyzed to describe the attributes of catechins and flavonol glycosides in China. A support vector machine (SVM) classifier was built to recognize the assamica variety with 94.2 % accuracy. Accumulation of (-)-epicatechin gallate (ECG) and flavonol di-glycosides was especially observed in assamica variety, while (-)-epigallocatechin gallate (EGCG) and flavonol tri-glycosides were obviously accumulated in sinensis variety. The ratios of ECG/EGCG and flavonol tri-glycosides/flavonol di-glycosides could be used as indicators for distinguishing the different varieties and cultivars. Accumulation pattern of catechins and flavonol glycosides were mainly dependent on the genetic background of the cultivars rather than plantation locations. The increased hydroxyl groups at the C-ring of catechins and the extended sugar chain at the B-ring of flavonol glycosides could be considered as important rules of metabolite change during tea plant evolution. The mechanism of accumulation of flavonoids in various varieties and cultivars was also discussed. [ABSTRACT FROM AUTHOR]

• Effect of fermentation method on Congou black tea quality was examined firstly. • Novel dynamic fermentation (RFM) was superior to traditional fermentation method. • Black tea with RFM had higher amino acids, theaflavins and thearubigins. • Black tea with RFM had lower tea polyphenols, catechins and theabrownins. • Amino acids and tea pigments were the key fermentation differential substances. This study aimed to investigate the effects of a novel dynamic fermentation method (DFM) on the biochemical components change and sensory quality formation of Congou black tea. It was found that the most drastic changes in biochemical components took place within 30 min of fermentation. The a value (redness) of liquor color, the reduction degree of catechins, polyphenol oxidase activity, the formation rate and contents of theaflavins and thearubigins, as well the content of amino acids were significantly higher under DFM than the traditional fermentation method. Sensory quality was also superior under DFM with the highest scores for liquor color, aroma, and taste. Partial least squares discrimination analysis (PLS-DA) indicated significant differences between DFM and the other two methods. Moreover, the loadings scatter plot and variables important in the projection (VIP) showed that amino acids, catechins, and tea pigments were the key differential substances among the fermentation methods. These results are expected to provide a theoretical basis and technical guidance for the improvement of black tea quality. [ABSTRACT FROM AUTHOR]

• Seasonal variation affects the phenolic profile of Tocklai tea cultivars • Phenolic contents reach a maximum level in monsoon season • Cultivars TV15, TV17 and TV23 have significantly higher total catechin content • Cultivars TV9, TV10 and TV11 have significantly higher EGCG content • Day length and temperature trigger variation in phenolic composition in tea shoots Two thirds of the tea growing area of North East India is covered by Tocklai vegetative (TV) cultivars. The present study investigates the principal catechins [(−)-epigallocatechin gallate (EGCG), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC), (−)-epicatechin (EC), and (+)-catechin (+C)], total catechin (TC) and caffeine content in thirty-one TV cultivars (TV1-TV31) and four popular cultivars, viz. Betjan, Kharijan, S.3A/3, and T.3E/3 in three harvesting seasons i.e., pre-monsoon, monsoon and autumn, along with their genetic diversity. The monsoon harvested crop showed the highest average content of TC, EGCG, ECG, and caffeine. The TC levels varied from 129 ± 0.03 to 214 ± 4.72, 151 ± 4.21 to 238 ± 8.41, and 121 ± 4.45 to 181 ± 5.82 mg g-1 in pre-monsoon, monsoon and autumn, respectively. The most predominant catechin EGCG varied from 52.2 ± 1.07 to 111 ± 1.24, 70.4 ± 1.03 to 141 ± 1.35, and 58.4 ± 2.47 to 108 ± 2.15 mg g-1in pre-monsoon, monsoon and autumn, respectively. Caffeine content varied from 27.1 ± 0.32 to 48.7 ± 0.50, 35.3 ± 1.56 to 55.0 ± 1.34 and 27.6 ± 1.11 to 40.7 ± 0.42 mg g-1 in pre-monsoon, monsoon and autumn, respectively. TC contents in cultivars TV23, TV17 and TV15; and EGCG contents in TV10, TV11, and TV9 were significantly higher (p ≤ 0.05) than for other cultivars. Environmental factors, viz. day length, sunlight, temperature across seasons might have induced seasonal variation in phenolic composition. [ABSTRACT FROM AUTHOR]

• Forced degradation and simultaneous determination of methylxanthines and tannins. • Guarana did not present degradation in acid and oxidative solutions. • Catechins of guarana had epimerization under alkaline conditions. • Guarana was unstable under photochemical conditions. • Guarana may exert a neuroprotective activity. Paullinia cupana Kunth is a compound with therapeutic potential due to the presence of methylxanthines and tannins. In this sense, the precise and safe quantification of these compounds is of fundamental importance. From this, the objective of this work was to develop and validate a stability-indicating RP-HPLC method for the simultaneous determination of theobromine, theophylline, caffeine, catechin and epicatechin in powdered guarana. In addition, the safety profile of guarana exposure in microglia cells was evaluated through different colorimetric and fluorimetric experiments. Chromatographic conditions suitable were obtained using RP-18 column (250 mm × 4.5 mm, 5 μm) at 280 nm. Mobile phase constituted of A: water (0.1 % trifluoroacetic acid pH 4.2) and B: methanol:acetonitrile (25:75 v/v) 90:10 v/v (A:B) at 1 mL.min−1 flow rate. The in vitro tests of cell viability, nitric oxide and formation of total reactive oxygen species levels demonstrated that when in contact with microglia cells, guarana presents safety concentrations of 3.91–15.63 mg.mL−1. The results demonstrated, specificity, linearity, precision, accuracy, and robustness of the proposed method. Based on in vitro tests, it is believed that, in these concentrations, guarana may exert a neuroprotective activity, preventing the activation of microglia, possibly due to the presence of bioactive molecules. [ABSTRACT FROM AUTHOR]

• Five red grape varieties were discriminated according to their anthocyanin profiles. • Subunit composition of grape skin proanthocyanidins depends on cultivar. • Harvest season influences more the structure of seed proanthocyanidins than cultivar. • Skin phenolic composition may be employed as grape variety discrimination tool. The knowledge of grapes phenolic content is proven to be critical for the vinification process and the improvement of wine quality. This study was undertaken to determine the phenolic composition and to employ the phenolic profile as a varietal discrimination tool in five Greek red grape varieties. Ninety grape samples from two seasons (2017 and 2018) were analyzed after extraction with organic solvents. Their proanthocyanidin profile, expressed as percentages of flavan-3-ols, was determined in both skins and seeds by employing phloroglucinolysis followed by HPLC-UV and MS detection, and anthocyanin profile was identified only in the skin extracts by HPLC-UV. Significant differences were observed in proanthocyanidin and anthocyanin profiles of skin extracts between the samples of different varieties, but not in seeds. (-)-Epicatechin was the main subunit in Mandilaria, Kotsifali, Agiorgitiko and Xinomavro grapes while (-)-epigallocatechin gallate in Mavrotragano. Malvidin-3- O -glucoside was the predominant pigment in all grape samples analyzed with the exception of Kotsifali skin extracts, where peonidin-3- O -glucoside was the most abundant anthocyanin. In addition, Mavrotragano skin extracts were the richest in delphinidin and petunidin-3- O -glucosides, while Agiorgitiko and Xinomavro contained the highest amount of malvidin-3- O -glucoside. The results underline the significance of the skin phenolic composition as a tool for the discrimination of the Greek red grape varieties. [ABSTRACT FROM AUTHOR]

• Sixty phenolic compounds were tentatively identified in old and young tea leaves. • Phenolic profiles of old and young tea leaves were significantly different. • Upon leaf aging, flavanols and phenolic acids decreased, whereas flavonols increased. • Degalloylation of phenolic compounds commonly occurred upon leaf maturation. • Phenolic profiles of old and young tea leaves were differentiated by 14 compounds. Old tea leaves (OTL), which are normally discarded as agricultural waste, are potential sources of tea phenolic compounds. However, little details are known about their phenolic composition. In this study, the phenolic profiles of OTL and young tea leaves (YTL) were compared by using ultra-high performance liquid chromatography coupled to hybrid quadrupole Orbitrap mass spectrometry (UHPLC-Q-Orbitrap-MS) analyses, with an untargeted approach. A total of 60 phenolic compounds were tentatively identified. Principal component analysis illustrated distinct differences in overall phenolic profiles between OTL and YTL. In particular, after maturation, flavanols and phenolic acids decreased 1.7- and 3.0-fold, respectively, whereas flavonols increased 1.5-fold. In addition, degalloylation commonly occurred with leaf maturation, as evidenced by a decrease in galloylated catechins and flavanol dimers upon aging. Furthermore, by applying linear discriminant analysis effect size (LEfSe) algorithm, 14 representative phenolic compounds were identified which underwent extensive quantitative changes upon leaf aging, including: rutin, epigallocatechin, epicatechin, epigallocatechin gallate, epicatechin gallate, and epiafzelechin gallate. In conclusion, this study provides detailed insights in the phenolic composition of old and young tea leaves, facilitating the future utilisation of OTL as a new and cost-effective source of tea phenolics. [ABSTRACT FROM AUTHOR]

• Tuber analysed showed phenolic acids and flavanoids of known bioactive potential. • Hydroxycinnamic acid derivatives were predominant in yacon tuber. • Yacon and purple sweet potato could be good source of important phenolic compounds. • Mashua was the only tuber that presented flavan-3-oles. • This is the first study about the elucidation of phenolic compounds in melloco. In this work, the phenolic compounds of four Andean tubers grown in Ecuador, such as yacon (Smallantus sonchifolius), mashua (Tropaeolum tuberosum), melloco (Ullucus tuberosus) and purple-sweet potato (Ipomea batatas) were analyzed by HPLC–DAD–ESI/MSn. Non-flavonoid compounds, such as hydroxycinnamic derivatives were identified in yacon, purple sweet potato and melloco samples, accounting for 100, 26 and 15% of the total of phenolic compounds, respectively. Mashua sample revealed the presence of flavan-3-ol monomers that were not found in the other samples, being (-)-epicatechin the most abundant (9.22 μg/g DM). Quercetin-3- O -rutinoside (40.6 μg/g DM), kaempferol- O -dirhamnosil-hexoside (29.5 μg/g DM) and kaempferol- O -dihexoside (46.22 μg/g DM) were the main flavonols present in mashua, melloco and purple sweet potato, respectively, being this last specie which presented the highest concentration in flavonols (89.32 μg/g DM). Purple sweet potato also had anthocyanins (157.16 μg/g DM), not detected in the other samples. The presence of these compounds and the consideration of the total phenolic content suggest the use of these Andean tubers as promising sources of natural antioxidants of wide use in the food industry. Therefore, these tubers could be considered as novel and inexpensive sources of bioactive compounds for their potential use in functional foods and nutraceuticals. [ABSTRACT FROM AUTHOR]