Tea Residue Research Articles

Tailoring tea residue-derived nitrogen-doped activated carbon for CO2 adsorption: influence of activation temperature and activating agents.

Embracing CO2 mitigation strategies, such as state-of-the-art CO2 capture technologies, is essential for effectively reducing atmospheric carbon levels and advancing global efforts toward a more sustainable future. In this context, adsorption sequestering techniques utilising carbon materials have emerged as promising candidates for CO2 capture. These materials have been extensively researched with a range of tuning methods to optimise their physicochemical features. In this study, an alteration of the N-doped activated carbon was successfully performed, utilizing tea residue as the carbon precursor and ammonia as the nitrogen source, facilitated through an impregnation procedure. With the objective of discovering the effect of diverse activation parameters on prepared adsorbent physicochemical properties, several selections of activating agents (AA) were investigated: KOH, H3PO4, ZnCl2, and NaOH, together with broad thermal activation temperature from 873 to 1173K. The best-performed adsorbents from the respective AC group were subjected to several characterisation analyses and found to the enhanced structural features, heteroatom doped-rich surface (i.e. N and O); together with AA-induced metal/mineral functionalization, the NaOH-used AC (NAC-N-1173) was the optimum-performed adsorbent with a promising 4.12mmol/g CO2 uptake capacity, higher than other prepared adsorbent including N-doped tea residue-derived char and commercialized AC with 175 and 325% higher, respectively.

Multi-Omics Reveals the Anti-Aging Effects and Mechanisms of Bound Polyphenols from Tea Residue Dietary Fiber in 3-MCPD-Induced Caenorhabditis elegans

Previous studies have shown that bound polyphenols from tea residue dietary fiber (TBP) were novel natural food ingredient with hypoglycemic activity, but the protective effects against aging have not been fully explored. This study investigated the potential of TBP to alleviate aging in Caenorhabditis elegans induced by 3-monochloropropane-1,2-diol and elucidated the underlying mechanisms through transcriptomic and metabolomic analyses. The results demonstrated that TBP markedly prolonged the lifespan of the nematodes, improved body morphology and locomotion, and effectively reduced reactive oxygen species and lipofuscin accumulation, while enhancing antioxidant defenses. Transcriptomic and metabolomic analyses further highlighted the critical role of the Insulin/Insulin-like Growth Factor 1 (insulin/IGF-1) signaling pathway in lifespan extension, with validation provided through gene expression and fluorescent mutants. These findings underscored the significant potential of TBP to counteract the adverse effects of 3-Monochloropropane-1,2-diol (3-MCPD) and extend lifespan, thereby providing a solid theoretical foundation for developing health products and exploring novel applications.

A novel magnetic S/N co-doped tea residue biochar applied to tetracycline adsorption in water environment

The issue of tetracycline (TC) contamination has attracted widespread attention. Adsorption technology has great potential for application in the field of TC remediation. This study achieved the production of nitrogen self-doped biochar using waste tea leaves as raw materials, and further improved its TC removal effect by doping sulfur elements. A recyclable high-performance TC adsorbent magnetic S/N co-doped tea residue biochar (MSNB) was obtained through ferromagnetic modification, which could be used as an effective TC adsorbent. The effects of MSNB dosage and initial solution pH on TC removal were evaluated. The recovery performance of MSNB adsorbent on TC was studied. The maximum adsorption performance at 298 K calculated using the Langmuir model was 140.76 mg g−1. The fitting results of adsorption kinetics indicated that chemical adsorption was the main factor affecting the adsorption reaction. After 5 cycles of adsorption, the removal of TC by MSNB remained above 88.30 %. This study could provide theoretical support for the treatment of tetracycline wastewater by biochar adsorption.

Biomass microcrystalline cellulose based solar evaporator with aligned channels for clean water and electricity co-generation

Solar-driven interfacial evaporation co-generation (SDIE-CG) technology can effectively solve problems such as low latent heat utilization in the evaporation process, which provides a reliable solution to the problem of hydropower shortage in remote areas. Herein, we report a tea residue microcrystalline cellulose (TMCC) aerogel (abbreviated as TCA), in which TMCC is regenerated by dissolution through the co-solvent method, and microcrystalline cellulose is rearranged by the directional slow freezing technique to get a TCA with a directional aligned pore structure, resulting in a good mechanical and salt-resistant property. Due to the internal doping of carbon black particles, the TCA has an average ultra-high absorbance of 97.46 %. The evaporation rate of TCA is up to 3.066 kg m−2h−1 under 3 kW m−2 illuminations. The maximum output voltage of the TCA is 44.801 mV under 2 kW m−2 illuminations through the introduction of a suitable wind-assisted hydropower generation device. In addition, the TCA can effectively purify the wastewater containing traditional Chinese medicine, and the chemical oxygen demand (COD) value in wastewater shows a significant decrease after treatment. It is worth noting that TCA can maintain structural integrity and stable evaporation performance in saltwater under extreme pH conditions (2<pH<11), and has potential application value in water treatment and cogeneration.

Preparation and stability of angiotensin-I-converting enzyme (ACE) inhibitory peptides from protein hydrolysate of Wuyi rock tea residues

ABSTRACT Wuyi rock tea residues, generated after brewing or aroma extraction, are rich in nutrients. This study aimed to prepare ACE inhibitory peptides from the protein hydrolysate of Wuyi rock tea residues and investigate their stability. The optimal proteolysis conditions for neutral protease were optimized as: a substrate concentration of 2% (w/v), pH 7.0, hydrolysis temperature of 45°C, enzymatic digestion time of 3 h, and enzyme dosage of 6800 U/g. Under these conditions, the ACE inhibition rate of protein hydrolysate of Wuyi rock tea residues reached 70.47 ± 0.29% at a concentration of 0.5 mg/mL. Additionally, the prepared ACE inhibitory peptides demonstrated excellent stability against acid, base, heat, and certain metal ions. These findings suggest that the proteins extracted from Wuyi rock tea residues can serve as a promising source to produce highly active ACE inhibitory peptides. These peptides could be utilized in the development of nutraceuticals, functional foods, and pharmaceuticals.

Analysis of 27 supervised machine learning models for the co-gasification assessment of peanut shell and spent tea residue in an open-core downdraft gasifier

The producer gas (PG) obtained through thermochemical processing of the various renewable biomass types contributes to Sustainable Development Goal-7 (SDG-7). Hence, this study examined 27 supervised and multiple-input single-output ML models in terms of performance metrics and accuracy to predict CO, H2, CH4, and CO2 compositions, as well as PG's HHV in the co-gasification of peanut shell (PS) and spent tea residue (STR). Multiple trial experiments were tested with various equivalence ratios (ERs) and mixing ratios (MRs) on a 90 m3/h gas-yield open-core, down-draft gasifier with air as the gasification medium. About 18 models were chosen after evaluating their performance metrics in estimating relevant parameters. The accuracy of those models is assessed based on 12 sample runs with varying ER and MR. The findings revealed that 16 models from the linear, neural network, support vector machine, Gaussian process, tree, and ensemble categories were reliable ML models. The chosen 16 models' R2 values for CO, H2, CH4, CO2, and HHVPG are above 0.931, 0.937, 0.962, 0.806, and 0.971, respectively, with the exception of TRE. Additionally, the models demonstrated a prediction accuracy of >95 % for all of the investigated parameters in the co-gasification of PS and STR when compared to random experimental runs.

Evaluating the performance effectiveness of briquettes made from coconut dreg charcoal (CDC), tea residue (TR), and cocoa pod (CP)

Abstract Environmental pollution, depletion of fossil fuels, and a significant rise in the human population are contributing to an increase in the greenhouse gas in the atmosphere. Addressing these challenges necessitates the production of clean, low-carbon emission, and sustainable bioenergy, such as briquettes, which can significantly contribute to knowledge and innovation. To assess the effectiveness of briquettes, their characteristics need to be tested using proximate analysis. In examining the characteristics of briquettes, the average moisture content of coconut dreg charcoal and tea residue (CDC+TR) measured 4.835%, contrasting with the 5.9% found in the cocoa pod (CP). The average ash content in CDC+TR was 2.351%, while CP recorded 3.2%. The average volatile matter in CDC+TR was 24.993%, while in CP, it was 31.5%. CDC+TR had an average fixed carbon of 67.815%, compared to CP of 59.5%. Furthermore, the average gross calorific value in CDC+TR was 4562.16 cal/g, whereas in CP, it was 4205.2 cal/g. In conclusion, CP briquettes could serve as an alternative energy source due to ease of production, low sulfur content, and favorable calorific value. CDC+TR, on the other hand, enhanced energy efficiency because of their lower moisture content, ash content, and volatile matter. Additionally, CDC+TR briquettes had higher fixed carbon and gross calorific values compared to CP, making them a suitable energy source.

Investigation into the adsorption mechanism of Fe(III) by biomass carbon derived from tea residue and its high-value conversion into bismuth ferrite for enhanced activation of peroxymonosulfate towards antibiotics degradation

Water pollution caused by heavy metals and antibiotics adversely affects human health. However, the harmful solid waste generated via traditional pollution removal processes significantly increases the recovery cost. Herein, we study the adsorption mechanism of hydrothermal activated carbon (AHTC) from tea residue on heavy metals, with AHTC having a good adsorption capacity of 699.0 mg/g for Fe(III). We then use one-step hydrothermal synthesis to produce an AHTC/bismuth ferrite composite (BFOC) material using solid waste to perform activation peroxymonosulfate to degrade antibiotics. The experimental results reveal that the BFOC exhibits good photocatalytic performance, with 94.60 % of the oxytetracycline (20 mg/L) sample degraded within 40 min. BFOC also shows catalytic activity against other antibiotics. The reaction mechanism of the catalyst and intermediate of the OTC reaction are also studied. This study offers a new strategy for the adsorption of heavy metals and the degradation of organic pollutants.

Effect of steam explosion pretreatment on the fermentation characteristics of polysaccharides from tea residue

Green tea residues are the by-product of tea processing and they contain a large number of bioactive ingredients. Steam explosion has been recognized as one of the most innovative pretreatments for modifying the physicochemical characteristic of polysaccharides from lignocellulosic materials. However, the comparison of biological activity of steam exploded (SE-GTR) and unexploded (UN-GTR) green tea residue polysaccharides was still unclear, which prompted the determination of the efficacy of steam explosion in tea residue resource utilization. In this study, the effects of two extracted polysaccharides UN-GTR and SE-GTR on human gut microbiota in vitro fermentation were conducted. The results showed that after steam explosion pretreatment, SE-GTR displayed more loose and porous structures, resulting in higher polysaccharide content (2483.44±0.5 μg/mg) compared to UN-GTR (1903.56±2.6 μg/mg). In addition, after 24 h fermentation, gut microbiota produced more beneficial metabolites by SE-GTR. The largest SCFAs produced among samples was acetic acid, propionic acid and butyric acid. Furthermore, SE-GTR could regulate the composition and diversity of microbial community, increasing the abundance of beneficial bacteria, such as Bifidobacterium. These results revealed that steam explosion pretreatment could be a promising and efficient approach to enhance the antioxidant activity and bioavailability of polysaccharides isolated from tea residues.

Removal of tetracycline in the water by a kind of S/N co-doped tea residue biochar

Tetracycline (TC) is widely present in the environment, and adsorption technology is a potential remediation method. S/N co-doped tea residue biochar (SNBC) was successfully prepared by hydrothermal carbonization method using tea residue as raw material. S was doped by Na2S2O3·5H2O, and N was doped by N in tea residue. The adsorption efficiency of SNBC could reach 94.16% when the concentration of TC was 100 mg L−1. The adsorption effect of SNBC on TC was 9.38 times more than that of unmodified biochar. Tea biochar had good adsorption effect at pH 4–9. The maximum adsorption capacity of 271 mg g−1 was calculated by the Langmuir isotherm model. The adsorption mechanism involved many mechanisms such as pore filling, π-π interaction and hydrogen bonding. The adsorbent prepared in this study could be used as an effective adsorbent in the treatment of TC wastewater.

Effects of biochars derived from different feedstocks and pyrolysis temperatures on the anaerobic digestion of kitchen waste

The aim of this work was to investigate the effects of biochars derived from different feedstocks and pyrolysis temperatures on the anaerobic digestion (AD) of kitchen waste (KW). Nine biomass feedstocks (corn straw (CS), Dicranopteris dichotoma (DD), bamboo (B), KW, tea residues (TR), mushroom cultivation waste (MW), cassava lees (CL), Chlorella (C), and sargassum (S)) were pyrolyzed at different temperatures (300 °C, 500 °C, and 800 °C). Biochar varied in physicochemical properties (e.g., specific surface area, total pore volume, and organic functional group) depending on both feedstock type and pyrolysis temperature. This further impacted the enrichment of functional microbial consortia and development of methanogenic pathways, resulting in a varied AD performance. The addition of biochars generated respectively from CS, MW, and S at 800 °C, 300 °C, and 500 °C significantly improved the maximum methane production rate (Rm) and methane yield, while other biochars enhanced either Rm or methane yield. Therefore, the efficacy of biochar on methanogenesis associated with both the feedstock type and pyrolysis temperature. The findings offer a beneficial reference for the selection and application of biochar to improve the AD performance.

Application of green tea residue-derived carbon dots in the detection of Fe3+ ions and imaging of Caco-2 cells

In this study, we successfully synthesized green luminescent carbon dots by using green tea residue as the precursor of carbon source. Based on the internal filter effect (IFE), the fluorescence emission intensity of the probe decreased significantly with the increase of Fe3 + concentration. Based on this, a linear relationship between Fe3 + concentration and the fluorescence emission intensity of the probe was established to semi-quantitatively detect Fe3 +. The results showed that the linear range was 1–400 μM, and the detection limit was 3.58 μM. In addition, the probe was further applied to actual samples, and it was found that the recovery rate was between 97.75% and 104.59%, and the relative standard deviation was below 1.81%. These findings underscore the considerable potential of the carbon dots for practical Fe3+ detection applications. In a further application, the fluorescent carbon dots were diluted and directly employed to stain Caco-2 cells. Remarkably, even after 10 and 20-fold dilutions, the Caco-2 cells displayed vivid fluorescence at the green excitation wavelength. This outcome suggests a promising avenue for the application of fluorescent carbon dots in the field of biology.

In-situ reshaping nano-biochar on electrode surface for machine learning assisted selective sensing of Pb2+ in real water samples

Surface engineering is an indispensable basic means to improve the properties of carbon nanomaterials and expand their application fields. Herein, tea residue was used as raw material to produce nano-biochar (NBC) by thermal decomposition method. Then the NBC was reshaped in situ on electrode surface to obtain electroreduced NBC (ErNBC) by cyclic voltammetry. After related material characterization, it is found that the properties of NBC are ideally reshaped after in situ electrochemical reduction, the size of NBC is reduced, the content of O element is increased, the hydrophilicity of NBC is enhanced, and the conductivity of NBC is improved. A model was constructed synchronously, and theoretical calculations were conducted to verify the changes in the material’s energy gap. Meanwhile, utilizing the structural properties of ErNBC, we develop an electrochemical sensor combined with machine learning for selective detection of Pb2+ in actual water samples with a satisfactory recovery rate.

Unveiling structure and performance of tea-derived cellulose nanocrystals

In this study, cellulose was extracted from black tea residues to produce black tea cellulose nanocrystals (BT-CNCs) using an optimized acid hydrolysis method. The structure and performance of BT-CNCs were evaluated. The results showed that the optimal conditions for acidolysis of BT-CNCs included a sulfuric acid concentration of 64 %, a solid-liquid ratio of 1:18 (w/v), a hydrolysis temperature of 45 °C, and a hydrolysis time of 50 min. The optimization process resulted in a 44.8 % increase in the yield of BT-CNCs, which exhibited a crystallinity of 68.57 % and were characterized by the typical cellulose I structure. The diameters of the particles range from 5 to 45 nm, and they exhibit aggregation behavior. Notably, BT-CNCs demonstrated excellent storage stability, and the Tyndall effect occurred when exposed to a single beam of light. Although the thermal stability of BT-CNCs decreased, their primary thermal degradation temperature remained above 200 °C. The colloidal nature of BT-CNCs was identified as a non-Newtonian fluid with “shear thinning” behavior. This study introduces a novel method to convert tea waste into BT-CNCs, increasing the yield of BT-CNCs and enhancing waste utilization. BT-CNCs hold promise for application in reinforced composites, offering substantial industrial value.

Advanced application of tea residue extracts rich in polyphenols for enhancing sludge dewaterability: Unraveling the role of pH regulation

Tea polyphenols (TPs), as a kind of derivatives from tea waste, were employed as a novel environmentally friendly bio-based sludge conditioner in this study. The findings showed that when TPs were applied at a dosage of 300 mg g−1 DS, the sludge CST0/CST ratio significantly increased to 1.90. pH regulation was found to markedly affect the dewatering efficiency of sludge. At pH 4, the CST0/CST rose to 2.86, coupled with a reduction in the specific resistance to filtration (SRF) from 6.69 × 1013 m kg−1 to 1.43 × 1013 m kg−1 and a decrease in the moisture content (MC) from 90.57% to 68.75%. TPs formed complexes and precipitated sludge proteins, as demonstrated by changes in the extracellular polymeric substances (EPS), viscosity, zeta potential, and particles size distribution. The optimization significance of acidification treatment on sludge structure disintegration, the interaction of TPs with EPS, and the removal of sludge proteins were elucidated. The research provided an ideal approach for the integrated utilization of biomass resources from tea waste and highlighted the potential application of TPs as an environmentally friendly conditioner in sludge dewatering.

Effects of Dried Tea Residues of Different Processing Techniques on the Nutritional Parameters, Fermentation Quality, and Bacterial Structure of Silaged Alfalfa.

The effects of dried tea residues on the nutritional parameters and fermentation quality, microbial community, and in vitro digestibility of alfalfa silage were investigated. In this study, dried tea residues generated from five different processing techniques (green tea, G; black tea, B; white tea, W; Pu'er raw tea, Z; Pu'er ripe tea, D) were added at two addition levels (5% and 10% fresh weight (FW)) to alfalfa and fermented for 90 days. The results showed that the tea residues increased the crude protein (CP) content (Z10: 23.85%), true protein nitrogen (TPN) content, DPPH, and ABST radical scavenging capacity, total antioxidant capacity (T-AOC), and in vitro dry matter digestibility (IVDMD) of the alfalfa silage. Moreover, the pH, ammonia-N (NH3-N) content, and acetic acid (AA) content decreased (p < 0.05). The effects of tea residues were promoted on these indicators with increasing tea residue addition. In addition, this study revealed that the influence of dried tea residues on the nutritional quality of alfalfa silage was greater than that on fermentation quality. Based on the nutrient composition, the addition of B or G to alfalfa silage can improve its silage quality, and these tea byproducts have the potential to be used as silage additives.

Valorization of cell wall polysaccharides extracted from Liubao brick tea residues: chemical, structural, and hypoglycemic properties.

Tea dregs, typically generated during the production of instant tea or tea beverages, have conventionally been regarded as waste material and routinely discarded. Nevertheless, contemporary research endeavors are concentrating on discovering efficient methods for utilizing the potential of this discarded resource. In this study, we employed a sequential extraction method using chemical chelating agents to extract and isolate four distinct cell wall polysaccharides, designated as CWTPS-1 through CWTPS-4, from the tea dregs of Liubao brick tea. A comprehensive investigation into their physicochemical, structural, and hypoglycemic properties was conducted. The analysis of chemical composition and physicochemical characteristics revealed that all four CWTPSs were characterized as acidic polysaccharides, albeit with varying chemical compositions and physicochemical attributes. Specifically, the xyloglucan fractions, CWTPS-3 and CWTPS-4, were found to be rich in glucose and xylose, displaying a more uniform molecular weight distribution, greater structural stability, and a more irregular surface compared to the others. Moreover, they exhibited a higher diversity of monosaccharide residues. Importantly, our research unveiled that all four CWTPSs exhibited the capacity to modulate key glucose-regulated and antioxidant enzyme activities within HepG2 cells via the IRS-1-PI3K/AKT signaling pathway, thereby ameliorating cellular insulin resistance. Furthermore, our correlation analysis highlighted significant associations between monosaccharide composition and neutral sugar content with the observed hypoglycemic activity of CWTPSs. This study highlights the potential of utilizing tea dregs as a valuable resource, making a significant contribution to the advancement of the tea industry. Furthermore, CWTPS-4 exhibits promising prospects for further development as a functional food ingredient or additive. © 2024 Society of Chemical Industry.

Pu-erh tea-derived cellulose exhibits superior water/oil holding capacity compared to black and green tea celluloses: A comprehensive analysis

In this study, residues from black, green, and Pu-erh teas were used as raw materials to extract cellulose through alkali treatment and two-stage bleaching process. The structure and properties of the tea celluloses were compared. The yield and purity of the cellulose ranged from 6.3% to 10.1% and 75.5%–88.9%, respectively. The celluloses exhibited a typical bundle fiber morphology and an I-type crystal structure, with the Iβ structure being the predominant allomorph. Crystallinity was highest in Pu-erh tea cellulose (54.8%), followed by black tea cellulose (52.6%), and green tea cellulose (47.4%). Green tea cellulose displayed the highest initial thermal degradation temperature, while Pu-erh tea cellulose had the lowest. Pu-erh tea cellulose showed the highest moisture absorption rate (12.6%), water holding capacity (10.1 g/g), and oil holding capacity (5.7 g/g), whereas these values were lowest in black tea cellulose. The correlation coefficient between Iβ structure content and water holding capacity is −0.90, and −1.00 with oil holding capacity. This study not only opens new pathways for the recycling of tea residues and their application in food packaging but also highlights the potential of tea-derived cellulose as an innovative material for dietary fiber resources with excellent water/oil holding capacities.

Utilization of the waste aqueous phase from tea residue hydrothermal carbonization for preparing active food packaging films

Hydrothermal carbonization (HTC) is an effective strategy for high-value utilization of tea residue (TR), and it was noticed the aqueous phase (AP) has not been extensively studied. This study aimed to investigate the chemical components and characteristics of the AP, and applied it in active food packaging films. The results showed that the total phenolic content of AP was 1.86 mg GAE/mL, and the main compounds in AP were organic acids, alcohols, and amino acids. The AP showed excellent antibacterial activity and antioxidant capacity. The active films were prepared using the casting method. The 4:7-AP/PVA film showed outstanding mechanical properties (tensile strength = 34.18 MPa, elongation at break = 458.67%), antioxidant ability (DPPH scavenging capacity 92.01%), antibacterial activity, water resistance and biocompatibility. The banana preservation test showed the AP/PVA films could successfully prolong the shelf-life of bananas and have the potential to be food packaging films.

Turning Waste into Wealth: Utilizing Trichoderma’s Solid-State Fermentation to Recycle Tea Residue for Tea Cutting Production

Trichoderma is a widely recognized plant-growth-promoting fungus that has been extensively utilized in various agricultural applications. However, research on the economic production of Trichoderma spores and their effects on tea cuttings must be further advanced. In this study, T. guizhouense NJAU 4742 (NJAU 4742) emerged as a growth-promoting strain for tea cuttings, and the spore-production conditions of NJAU 4742 attained through solid-state fermentation (SSF) using tea residues were optimized. In a pot experiment, nursery substrates containing different concentrations of NJAU 4742 spores were tested for their influence on tea cutting growth and the rhizosphere fungal community. The optimal conditions for spore yield were determined as a 7:3 (w/w) ratio of tea residue to rice bran, a material thickness of 3 cm, an inoculum concentration of 15% (v/w), and an incubation time of 4 days, resulting in a spore count of 1.8 × 109 CFU/g. Applying NJAU 4742 spore products significantly increased the biomass of tea cuttings and influenced the fungal community composition. Moreover, higher concentrations of NJAU 4742 spores yielded better growth performance, and applying nursery substrate with 1.0 × 107 CFU/mL spores was the most economically viable option. Notably, among the top ten fungal genera with the highest relative abundance, Trichoderma showed a positive correlation with the fresh weight of tea cuttings, while the others exhibited a negative correlation. Overall, utilizing tea residue for SSF to produce NJAU 4742 was a feasible approach, and the application of NJAU 4742 spores enhanced the growth of tea cuttings by increasing the relative abundance of Trichoderma.