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In this study, biopolymer composites based on chitosan (CS) with enhanced optical properties were functionalized using Manganese metal complexes and black tea solution dyes. The results indicate that CS with Mn 2+ -complexes can produce polymer hybrids with high absorption, high refractive index and controlled optical band gaps, with a significant reduction from 6.24 eV to 1.21 eV. The refractive index and optical dielectric constant measurements show that the doped CS films have more charge carriers and traps than those in pure CS films. The Lorentz-Drude model was used to derive several significant optical parameters, and the W-D model was utilized to calculate the optical moments M -1 changing from 0.35 to 2.13 and M -3 changing from 0.005 to 0.4. It was shown that the doped samples have larger Urbach energy than pure film, increased from 0.29 to 0.55 eV. Tauc and ASF model was also used to calculate the electronic transitions, band structure, and optical characteristics. Bandgap energy based on Tauc model at m = 2, 1/3, 1/2, and 2/3 are 1.77, 1.54, 1.47, and 1.37 eV, based on ASF model are 1.52, 1.42, 1.69, and 1.47 eV, respectively. As a result of changes in the optical diffraction parameters the optical mobility ( ) changed from 1.67 to 1.27 and optical resistivity from 9.36 × 10 –27 to 4.0 × 10 –29 . The dopped samples show an increase in their linear optical susceptibility, third-order nonlinear optical susceptibility and nonlinear refractive indices, changing from 3.165 × 10 –15 to 2.831 × 10 –12 esu. Finally, light propagation velocities, surface resistance, and thermal emissivity were also examined.

Headspace Solid-Phase Microextraction-Gas Chromatography-Mass Spectroscopy (HS–SPME–GC–MS) and Odor Activity Value (OAV) analysis were used to characterize the aroma components of Chuanhong congou black tea. The key aroma compounds were screened by combining Principal Component Analysis (PCA), Orthogonal Partial Least Squares Discrimination Analysis (OPLS-DA) model, and Variable Importance Projection (VIP). The perceived interactions among the key aroma compounds in the tea were analyzed using Feller summation model and S-curve. Thus, 89 volatile aroma compounds were identified in the samples. Thirty key aroma compounds (OAV > 1) were screened by OAV, PCA (R2Xcum = 0.941, Q2cum = 0.897), and OPLS-DA (R2cum > 0.9, Q2cum > 0.9). Results showed a good model fit and more effective clustering of the samples. Finally, eight key aroma compounds were screened, which included trans-2-Hexenal, 2-hexenal, linalool, hexanal, phenylacetaldehyde, methyl salicylate, benzaldehyde, and (E)-linalool oxide (furan type). The perceived interactive relationships among the key aroma substances showed that 12 of the 15 groups of binary compounds had masking effects and 3 groups had additive effects. The results would serve as a reference for improving the quality of Chuanhong congou black tea.

Changes in key odorants of shaken black tea (SBT) during its manufacture were determined using headspace solid-phase microextraction (HS-SPME) combined with comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC × GC–TOFMS) and multivariate data analysis. A total of 241 volatiles was identified, comprising 49 aldehydes, 40 esters, 29 alcohols, 34 ketones, 30 aromatics, 24 alkenes, 17 alkanes, 13 furans, and 5 other compounds. A total of 27 volatiles had average relative odor activity values (rOAVs) greater than 1, among which (E)-β-ionone, (E,Z)-2,6-nonadienal, and 1-octen-3-one exhibited the highest values. According to the criteria of variable importance in projection (VIP) > 1, p < 0.05, and |log2FC| > 1, 61 discriminatory volatile compounds were screened out, of which 26 substances were shared in the shaking stage (FL vs. S1, S1 vs. S2, S2 vs. S3). The results of the orthogonal partial least squares discriminate analysis (OPLS-DA) differentiated the influence of shaking, fermentation, and drying processes on the formation of volatile compounds in SBT. In particular, (Z)-3-hexenol, (Z)-hexanoic acid, 3-hexenyl ester, (E)-β-farnesene, and indole mainly formed in the shaking stage, which promoted the formation of the floral and fruity flavor of black tea. This study enriches the basic theory of black tea flavor quality and provide the theoretical basis for the further development of aroma quality control.

The spent black tea extract was utilized in order to synthesize the spent black tea silver nanoparticles (SBT-AgNPs). Various parameters were tested to yield the best production of SBT-AgNPs. The characterization was conducted by X-Ray diffraction, Scanning electron microscopy, Zeta potential and energy dispersive X-ray (EDX). The XRD analysis showed hkl planes corresponding to (111), (200), (220), (311) planes at 2θ theta deg 38.3°, 40.8°, 64.5°, and 74.2°. The scanning electron microscopy reported the plate like round shaped morphology of the AgNPs. The zeta potential was examined to be -17.5 mV and a size distribution by intensity of 157.6 d. nm was observed. The EDX was employed to determine the purity of samples by reporting a strong peak of silver (Ag). The degradation activity was examined by photocatalytic removal of methylene blue and malachite green dyes from textile wastewater. The textile wastewater showed a decrease of methylene blue by 25% and 58.3%. The malachite green was also reduced by 33.3% and 60%, which was remarkably significant owing to the presence of the complex factor in the natural environment. The study sets a promising record to harbor the full potential of available food waste resource, such as spent black tea to form SBT-AgNPs and its application in the dye removal from textile waste. The multifaceted outcomes of this study resulted in an eco-friendly procedure, thereby reusing the waste material for environmental cleanup.

Value creation through waste recycling is important for a sustainable society and future. In particular, biomass, which is based on crops, is a great recyclable resource that can be converted into useful materials. Black tea is one of the most cultivated agricultural products in the world and is mostly discarded after brewing. Herein, we report the application of black tea waste biomass as electrode material for supercapacitors through the activation of biomass hydrochar under various conditions. Raw black tea was converted into hydrochar via a hydrothermal carbonization process and then activated with potassium hydroxide (KOH) to provide a large surface area and porous structure. The activation temperature and ratio of KOH were controlled to synthesize the optimal black tea carbon (BTC) with a large surface area and porosity suitable for use as electrode material. This method suggests a direction in which the enormous amount of biomass, which is simply discarded, can be utilized in the energy storage system. The synthesized optimal BTC has a large surface area of 1062 m2 and specific capacitance up to 200 F∙g−1 at 1 mV∙s−1. Moreover, it has 98.8% retention of charge–discharge capacitance after 2000 cycles at the current density of 5 A∙g−1.

Tea egg is a Chinese traditional snack and leisure food, fresh chicken eggs and tea are the main ingredients. The influence of tea is the most important one, because the polyphenols in different teas can affect the egg white gel (EGL) and will impact the quality and flavour of tea eggs. To investigate the effects of tea on the physicochemical characteristics of EGL during tea egg making, the common used tea (green and black tea), and their usual physical form (in leaf and powder) were selected, respectively. The results indicated that the physicochemical characteristics of EGL were more susceptible to green tea than black tea. EGL also had different results on the physical form of tea. When the tea concentration ranged from 1 to 12 g/100 mL (per gram dry tea in 100 mL of water), the soluble protein content and surface hydrophobicity in the EGL were both direct proportional to the tea concentration, whereas the pH exhibited an inverse relationship. The water holding capacity in green tea groups was like an inverted “U”, but it was kept increased in black tea groups. The content of free sulfhydryl groups in tea leaf groups was like an asymmetric inverted “V”, but it was positive correlation with the amount of tea in powder groups. Considering only the physicochemical properties of protein gel in egg white, green tea in leaf form of 6 g/100mL could make eggs with the best gel quality and stronger tea flavour. This study will standardize tea eggs making, and promote the sharing of traditional Chinese cuisine with the global community.

The efficiency in the capabilities to store and release antioxidants depends on the film morphology and its manufacturing process, as well as on the type and methodology used to obtain the polyphenol extracts. Here, hydroalcoholic extracts of black tea polyphenols (BT) were obtained and dropped onto different polyvinyl alcohol (PVA) aqueous solutions (water or BT aqueous extract with and without citric acid, CA) to obtain three unusual PVA electrospun mats containing polyphenol nanoparticles within their nanofibers. It was shown that the mat obtained through the nanoparticles precipitated in BT aqueous extract PVA solution presented the highest total polyphenol content and antioxidant activity, and that the addition of CA as an esterifier or PVA crosslinker interfered with the polyphenols. The release kinetics in different food simulants (hydrophilic, lipophilic and acidic) were fitted using Fick’s diffusion law and Peppas’ and Weibull’s models, showing that polymer chain relaxation is the main mechanism in all food simulants except for the acidic, which presented an abrupt release by Fick’s diffusion mechanism of about 60% before being controlled. This research provides a strategy for the development of promising controlled-release materials for active food packaging, mainly for hydrophilic and acidic food products.

Yunnan Congou black tea (YCBT) is a typical black tea in China, and is rich in theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs). However, the influence of the fermentation temperature and time on the liquor and appearance color and the correlation between the tea pigments and its color attributes remain unclear. We investigated the effects of the fermentation temperature and time on the color attributes and tea pigments of YCBT. A low fermentation temperature was beneficial to maintain a bright orange-red liquor color and promote the accumulation of TFs and TRs. In contrast, a high temperature gave the liquor a glossy appearance and was beneficial for the formation of TBs. A correlation analysis showed that the 10TFRB index best represented the contribution of tea pigments to the quality of black tea. Moreover, TRs and TBs content prediction models were established based on the liquor L and H values, where the former value can be used as an important index to judge the fermentation process. This study will further enrich the theory of black tea processing chemistry and provide technical support for the precise and directional production of black tea.

Ancient bud black tea (ABBT) is a special kind of black tea (BT) made from the bud of ancient tea tree. However, there is limited information about its chemical composition and the effects of shoot maturity and fermentation. By UHPLC-HRMS, 208 compounds including catechins, flavonoids, phenolic acids, alkaloids and others were qualitatively and quantitatively analyzed in ABBT. By comparison with traditional BT made from one bud with multiple leaves, it was suggested that the shoot maturity has great effects on the chemical profile of BT. Most of the detected compounds exhibited lower content in ABBT, while only a little number of compounds (e.g., theaflavin-3′-gallate, theaflavin-3-gallate, theaflavin-3,3′-gallate, quercitrin, isoquercitrin, and quinic acid) showed significantly higher contents in ABBT. During fermentation, the contents of these compounds varied obviously but with inconsistent trends. Simple catechins (e.g., EC, EGCG), dimers of catechins and their derivatives (e.g., prodelphinidin B2) showed an inconsistent decreasing trend, while oxidative polymerization products such as theaflavin-3,3′-gallate and theasinensin A showed a continuous increasing trend of content. Additionally, the contents of free phenolic acids, flavonoids, caffeine and amino acids showed a decreasing trend of content, while acylated phenolic acids exhibited an opposite trend. As a result, this work revealed the chemical profile of ABBT and enhanced our understanding with respect to the effects of shoot maturity and fermentation.

A fruity aroma is regarded as an important factor in the evaluation of black tea quality. However, the compounds contributing to a particularly fruity aroma still garner less attention. In this study, we aimed to identify the aroma-active compounds of the peach-like aroma of Jinmudan black tea (JBT). We used gas chromatography–mass spectrometry (GC-MS) to reveal the profile of the chemical compounds integrated into JBT and identified terpenoids, heterocyclic, and esters that contribute to its floral and fruity aroma. Under the PCA and PLS-DA modes, JBT and Fuyun NO. 6 black tea (FBT) can be divided into two classes, respectively (class 1 and class 2); several compounds, including indole, methyl salicylate, and δ-decalactone, have a higher VIP value (Variable Importance in Projection), and it has been found that δ-decalactone was the characteristic aromatic compound of peach fruit. Gas chromatography–olfactometry (GC-O) and the odor activity value (OAV) indicated that, in JBT, linalool, phenylacetaldehyde, and δ-decalactone could be considered aroma-active compounds (AACs). However, in FBT, the high content of heterocyclic compounds contribute to its caramel-like aroma. As for the biochemical compounds measurement, JBT has a higher content of theaflavins (TFs), thearubigins (TRs), and flavonoids. These results provide a theoretical basis for the quality and processing improvement in JBT.