Isolation and characterization of thermo-tolerant polyphenol oxidases in a black tea infusion

Integration of intelligent sensory evaluation, metabolomics, quantification, and enzyme activity analysis to elucidate the influence of first-drying methods on the flavor formation of congou black tea and its underlying mechanism

First-drying is a crucial step in black tea processing. Herein, the influence of different first-drying methods on black tea flavor formation was investigated, including box-hot air first-drying (BFD), roller first-drying, and microwave first-drying. Electronic tongue and color difference revealed distinct taste profiles (especially in bitter, astringency, sweet, umami) and liquor colors among three groups. Quantification and metabolomics analysis revealed that tea pigments (theaflavins, thearubigins), catechins, and other 34 metabolites including dimeric/trimeric catechins, amino acids and derivatives, flavonols and flavonol/flavone glycosides, phenolic acids, etc., were key differential components. The evolution of key metabolites, polyphenol oxidase (PPO) and peroxidase (POD) activities were tracked during drying. BFD exhibited significantly slower enzyme inactivation rate. Multiple conversions were possibly involved in drying, including catechins conversion (polymerization, degalloylation, epimerization), hydrolysis of flavonol-O-glycosides and phenolic acid esters, flavone-C-glycosides synthesis, etc., driven by the remaining PPO and POD activities and heat. Moreover, validation batch further verified the result.

Lily bulb polyphenol oxidase obtained via an optimized multi-stage separation strategy for structural analysis and browning mechanism elucidation

An optimized multi-stage separation strategy was developed to purify lily bulb polyphenol oxidase (PPO) for revealing its molecular structure. The PPO was purified 14.64-fold with high specific activity of 153,900 U/mg via optimized conditions of phosphate buffer pH (6.5), solid-liquid ratio (1:3), PVPP content (2 %), extraction time (4 h), followed by 30 %-50 % ammonium sulfate, diethylaminoethyl ion-exchange chromatography (0.1 M NaCl), and size exclusion chromatography. The PPO was identified as a dimeric protein with molecular weight of 135 kDa, containing 58.79 % random coil, 20.78 % α-helix, 17.41 % β-folding, and 3.02 % β-corner. The three-dimensional structure via homology modeling suggested that active center CuA bound to His151, His172, and His181, CuB bound to His307, His311, and His341. Furthermore, molecular docking indicated that its Phe337 and Tyr312 residues were catalytic cavity gates of catechol and 4-methylcatechol, respectively. Therefore, this study successfully analyzed purified PPO structure and further provided a theoretical foundation for its browning mechanism.

Biological potential and mechanisms of Tea's bioactive compounds: An Updated review

BACKGROUND

Tea (Camellia sinensis) has a rich history and is widely consumed across many countries, and is categorized into green tea, white tea, oolong tea, yellow tea, black tea, and dark tea based on the level of fermentation. Based on a review of previous literature, the commonly recognized bioactive substances in tea include tea polyphenols, amino acids, polysaccharides, alkaloids, terpenoids, macro minerals, trace elements, and vitamins, which have been known to have various potential health benefits, such as anticancer, antioxidant, anti-inflammatory, anti-diabetes, and anti-obesity properties, cardiovascular protection, immune regulation, and control of the intestinal microbiota. Most studies have only pointed out the characteristics of tea's bioactivities, so a comprehensive summary of the pharmacological characteristics and mechanisms of tea's bioactivities and their use risks are vital.

AIM OF REVIEW

This paper aims to summarize tea's bioactive substances of tea and their pharmacological characteristics and mechanisms, providing a scientific basis for the application of bioactive substances in tea and outlining future research directions for the study of bioactive substances in tea.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review summarizes the main biologically active substances, pharmacological effects, and mechanisms and discusses the potential risks. It may help researchers grasp more comprehensive progress in the study of tea bioactive substances to further promote the application of tea as a natural bioactive substance in the medical field.

Purification of polyphenol oxidase from tea (Camellia sinensis) using three-phase partitioning with a green deep eutectic solvent

In this study, tea polyphenol oxidase (PPO) was purified via three-phase partitioning (TPP) using a deep eutectic solvent (DES) instead of t-butanol. First, the properties of 13 types of synthesized DESs were characterized, and DES-7 (thymol/dodecanoic acid) was selected as the best alternative solvent. The process parameters were optimized using response surface methodology. The experimental results revealed that when the (NH4)2SO4 concentration, DES to crude extract ratio, extraction time, and pH were 41%, 0.5:1, 75 min, and 5.6, respectively, the recovery and purification fold of tea PPO were 78.44% and 8.26, respectively. SDS-PAGE and native-PAGE were used to analyze the PPO before and after purification of the TTP system, and the molecular weight and purification effect of PPO were detected. Moreover, the DES could be recovered and recycled. The results indicate an environmentally friendly and stable DES, and provide a reference for the large-scale application of TPP to extract PPO.

Recent Advances Regarding Polyphenol Oxidase in Camellia sinensis: Extraction, Purification, Characterization, and Application

Polyphenol oxidase (PPO) is an important metalloenzyme in the tea plant (Camellia sinensis). However, there has recently been a lack of comprehensive reviews on Camellia sinensis PPO. In this study, the methods for extracting PPO from Camellia sinensis, including acetone extraction, buffer extraction, and surfactant extraction, are compared in detail. The main purification methods for Camellia sinensis PPO, such as ammonium sulfate precipitation, three-phase partitioning, dialysis, ultrafiltration, ion exchange chromatography, gel filtration chromatography, and affinity chromatography, are summarized. PPOs from different sources of tea plants are characterized and systematically compared in terms of optimal pH, optimal temperature, molecular weight, substrate specificity, and activators and inhibitors. In addition, the applications of PPO in tea processing and the in vitro synthesis of theaflavins are outlined. In this review, detailed research regarding the extraction, purification, properties, and application of Camellia sinensis PPO is summarized to provide a reference for further research on PPO.

Widely targeted metabolomics reveals the effect of different raw materials and drying methods on the quality of instant tea

Introduction

Instant teas are particularly rich in tea polyphenols and caffeine and have great potential as food ingredients or additives to improve the quality of food and enhance their nutritional and commercial value.

Methods

To determine the relationships between raw material, drying method, and sensory and other quality attributes, instant teas were prepared from three tea varieties, namely black, green and jasmine tea, using two drying methods, namely spray-drying (SD) and freeze-drying (FD).

Results

Both the raw tea material and drying method influenced the quality of the finished instant teas. Black tea was quality stable under two drying, while green tea taste deteriorated much after SD. Jasmine tea must be produced from FD due to huge aroma deterioration after SD. FD produced instant tea with higher sensory quality, which was attributed to the lower processing temperature. Chemical compositional analysis and widely targeted metabolomics revealed that SD caused greater degradation of tea biochemical components. The flavonoids content changed markedly after drying, and metabolomics, combined with OPLS-DA, was able to differentiate the three varieties of tea. Instant tea preparations via SD often lost a large proportion of the original tea aroma compounds, but FD minimized the loss of floral and fruity aroma compounds. Changes in the tea flavonoids composition, especially during drying, contributed to the flavor development of instant tea.

Discussion

These results will provide an practicle method for high-quality instant tea production through choosing proper raw tea material and lowering down drying temperature with non-thermal technologies like FD.

Incidental nanoparticles in black tea alleviate DSS-induced ulcerative colitis in BALB/c mice

As the dominant herbal drink consumed worldwide, black tea exhibits various health promoting benefits including amelioration of inflammatory bowel diseases. Despite extensive studies on the tea's components, little is known about the bioactivities of nanoparticles (NPs) which were incidentally assembled in the tea infusion and represent the major components. This study investigated the alleviative effects of black tea infusion, the isolated black tea NPs, and a mixture of caffeine, epigallocatechin-3-gallate, gallic acid and epicatechin gallate on dextran sodium sulfate (DSS)-induced ulcerative colitis. The results showed that both the black tea infusion and the NPs significantly alleviated colitis, suppressed the mRNA levels of pro-inflammatory cytokines TNF-α, IL-6, and IL-1β, and suppressed the DSS-induced loss of cell-cell junction proteins (e.g., E-cadherin, ZO-1, and claudin-1) and increase of p-STAT3. The mixture of four tea components, which is the analogue of bioactive payloads carried by the NPs, was much less effective than the tea infusion and NPs. It shows that the NPs elevate the efficiency of polyphenols and caffeine in black tea in restoring the intercellular connection in the intestine, inhibiting mucosal inflammation, and alleviating ulcerative colitis. This work may inspire the development of tea-based therapeutics for treating inflammatory bowel diseases and have wide influences on value-added processing, quality evaluation, functionalization, and innovation of tea and other plant-based beverages.

Substrate specificity of polyphenol oxidase and its selectivity towards polyphenols: Unlocking the browning mechanism of fresh lotus root (Nelumbo nucifera Gaertn.)

Polyphenol oxidase (PPO) causes the browning of lotus roots (LR), negatively affecting their nutrition and shelf-life. This study aimed to explore the specific selectivity of PPO toward polyphenol substrates, thus unlocking the browning mechanism of fresh LR. Results showed that two highly homologous PPOs were identified in LR and exhibited the highest catalytic activity at 35 ℃ and pH 6.5. Furthermore, the substrate specificity study revealed (-)-epigallocatechin had the lowest Km among the polyphenols identified in LR, while (+)-catechin showed the highest Vmax. The molecular docking further clarified that (-)-epigallocatechin exhibited lower docking energy and formed more hydrogen bonds and Pi-Alkyl interactions with LR PPO than (+)-catechin, while (+)-catechin entered the active cavity of PPO more quickly due to its smaller structure, both of which enhance their affinity to PPO. Thus, (+)-catechin and (-)-epigallocatechin are the most specific substrates responsible for the browning mechanism of fresh LR.

A comprehensive review of polyphenol oxidase in tea (Camellia sinensis): Physiological characteristics, oxidation manufacturing, and biosynthesis of functional constituents

Polyphenol oxidase (PPO) is a metalloenzyme with a type III copper core that is abundant in nature. As one of the most essential enzymes in the tea plant (Camellia sinensis), the further regulation of PPO is critical for enhancing defensive responses, cultivating high-quality germplasm resources of tea plants, and producing tea products that are both functional and sensory qualities. Due to their physiological and pharmacological values, the constituents from the oxidative polymerization of PPO in tea manufacturing may serve as functional foods to prevent and treat chronic non-communicable diseases. However, current knowledge of the utilization of PPO in the tea industry is only available from scattered sources, and a more comprehensive study is required to reveal the relationship between PPO and tea obviously. A more comprehensive review of the role of PPO in tea was reported for the first time, as its classification, catalytic mechanism, and utilization in modulating tea flavors, compositions, and nutrition, along with the relationships between PPO-mediated enzymatic reactions and the formation of functional constituents in tea, and the techniques for the modification and application of PPO based on modern enzymology and synthetic biology are summarized and suggested in this article.

Purification, characterization and inactivation kinetics of polyphenol oxidase extracted from Cistanche deserticola

PPO was purified from Cistanche deserticola, and its enzymatic characteristics were clarified. It was found that microwave treatment was an efficient way to inactivate PPO. Polyphenol oxidase (PPO) from Cistanche deserticola was obtained and purified through an acetone precipitation and anion exchange column, the enzymatic characteristics and inactivation kinetics of PPO were studied. The specific activity of PPO was 73135.15 ± 6625.7 U/mg after purification, the purification multiple was 48.91 ± 4.43 times, and the recovery was 30.96 ± 0.27%. The molecular weight of the PPO component is about 66 kDa by SDS-PAGE analysis. The optimum substrate of PPO was catechol (V_max = 0.048 U/mL, K_m = 21.70 mM) and the optimum temperature and pH were 30 °C and 7, respectively. When the temperature is above 50 °C, pH < 3 or pH > 10, the enzyme activity can be significantly inhibited. The first-order kinetic fitting shows that microwave inactivation has lesser k values, larger D values and shorter t_1/2. It was found that microwave treatment is considered as an efficient and feasible way to inactive PPO by comparing the Z values and E_a values of the two thermal treatments.

Relationship between the Grade and the Characteristic Flavor of PCT (Panyong Congou Black Tea)

Panyong Congou black tea (PCT) is one of the most representative and historically famous Congou black teas in China and has been gaining more and more attention for its beneficial health properties. Currently, four grades of PCT are available, based on the raw leaf materials and consumer palatability. The chemical profiles distinguishing different grades of PCT are yet to be defined, nor has the relationship with grade been evaluated. In the present study, chemometric analysis showed that epigallocatechin (EGC), catechin (C), polyphenols, gallic acid (GA), and free amino acids are grade related bio-markers of PCT. These compounds are associated with the sweet and mellow aftertaste of PCT. A total of 34 volatile components were identified, of which the three component types with the highest relative percentages were alcohols (51.34–52.51%), ketones (27.31–30.28%), and aldehydes (12.70–13.18%). Additionally, our results revealed that sweet floral and fruity aromas were positively correlated with six volatile organic compounds (VOCs), 1-pentanol, propyl hexanoate, linalool, cyclohexanone, hexanal, and 2,5-dimethylpyrazine. Clear discrimination was achieved using orthogonal projections to latent structures discriminant analysis (OPLS-DA). The findings provide vital information on the characteristic flavor of each grade of PCT.

The unexpected flavone synthase-like activity of polyphenol oxidase in tomato

The biosynthesis of flavones has drawn considerable attention. However, the presence of flavones and their biosynthesis in tomato (Solanum lycopersicum) remain unclear. Here, we confirmed that flavones are present in MicroTom tomato and unexpectedly found that a tomato polyphenol oxidase (SlPPO F) possesses a flavone synthase-like activity and catalyzes the conversion of eriodictyol to luteolin without the need for any cofactor. SlPPO F showed a similar K_m value to that of other polyphenol oxidases, and could be inhibited by ascorbic acid. The flavone synthase-like activity of SlPPO F exhibited strict substrate specificity and only accepted flavanones with two hydroxyl groups (3' and 4') on the B ring as substrates. SlPPO F showed higher catalytic efficiency and better thermostability than type I flavone synthase from Apium graveolens, suggesting its possible application in enzyme engineering. In summary, we identified flavones in tomato and unraveled a polyphenol oxidase exhibiting flavone synthase-like activity.

Biochemical studies of enzyme-induced browning of African bush mango (Irvingia gabonensis) fruit pulp

The purpose of this study was to examine the biochemical properties of African bush mango (Irvingia gabonensis) pulp PPO. PPO was purified from I. gabonensis fruit pulp in three steps and characterized. A purification fold of 343 with specific activity of 216 U/mg and 13% recovery were obtained as well as molecular weight of 32.67 kDa was observed. The optimum pH and temperature were found to be pH 7.0 and 50 °C respectively while the enzyme showed instability at low pH 2-4 with total inactivation at pH 2 but maximal at pH 5-9 with remaining residual activity of 60-90%, whereas, total enzyme activity inactivation was observed at 90 °C. However, Cu²⁺, Fe²⁺ and Mg²⁺ enhanced the PPO activity but inhibited by Ca²⁺, Ba²⁺, K⁺ and Na⁺. Notably, purified PPO was inactivated completely by urea at concentration above 10 mM while K_m and V_max values were estimated to be 7.34 mM and 0.36 U/min for catechol, 10.76 mM and 0.30 U/min for _L-DOPA, and 14.90 mM and 0.26 U/min for tyrosine, respectively. The activity of PPO in I. gabonensis fruit and its juicy product could be controlled at high temperature in acidified medium.