Advances in bioconversion of spent tea leaves to value-added products

Sustainable environmental practices of tea waste-a comprehensive review

Tea, the major beverage worldwide, is one of the oldest commercial commodities traded from ancient times. Apart from many of its advantages, including health, socio-economic, climatic, and agro-ecological values, FAO has recognized that the tea value chain covering its growth in the field, processing and marketing, and finally, the hot cup at the user's hand needs to be made sustainable during all these stages. Tea generates a lot of waste in different forms in different stages of its growth and processing, and these wastes, if not managed properly, may cause environmental pollution. A planned utilization of these wastes as feedstocks for various processes can generate more income, create rural livelihood opportunities, help grow tea environmentally sustainable, avoid GHG emissions, and make a real contribution to SDGs. Thermochemical and biological conversion of tea wastes generates value-added products. This review provides an overview on the impacts of the tea wastes on the environment, tea waste valorization processes, and applications of value-added products. The application of value-added products for energy generation, wastewater treatment, soil conditioners, adsorbents, biofertilizers, food additives, dietary supplements, animal feed bioactive chemicals, dye, colourant, and phytochemicals has been reviewed. Further, the challenges in sustainable utilization of tea wastes and opportunities for commercial exploitation of value-added products from tea wastes have been reviewed.

New Eco-Friendly Thermal Insulation and Sound Absorption Composite Materials Derived from Waste Black Tea Bags and Date Palm Tree Surface Fibers

A tremendous amount of waste black tea bags (BTBs) and date palm surface fibers (DPSFs), at the end of their life cycle, end up in landfills, leading to increased pollution and an increase in the negative impact on the environment. Therefore, this study aims to utilize these normally wasted materials efficiently by developing new composite materials for thermal insulation and sound absorption. Five insulation composite boards were developed, two were bound (BTB or DPSF with polyvinyl Acetate resin (PVA)) and three were hybrids (BTB, DPSF, and resin). In addition, the loose raw waste materials (BTB and DPSF) were tested separately with no binder. Thermal conductivity and sound absorption coefficients were determined for all boards. Thermal stability analysis was reported for the components of the tea bag (string, label, and bag) and one of the composite hybrid boards. Mechanical properties of the boards such as flexural strain, flexural stress, and flexural elastic modulus were determined for the bound and hybrid composites. The results showed that the thermal conductivity coefficients for all the hybrid composite sample boards are less than 0.07 at the ambient temperature of 24 °C and they were enhanced as the BTB ratio was reduced in the hybrid composite boards. The noise reduction coefficient for bound and all hybrid composite samples is greater than 0.37. The composite samples are thermally stable up to 291 °C. Most composite samples have a high flexure modulus between 4.3 MPa and 10.5 MPa. The tea bag raw materials and the composite samples have a low moisture content below 2.25%. These output results seem promising and encouraging using such developed sample boards as eco-friendly thermal insulation and sound absorption and competing with the synthetic ones developed from petrochemicals in building insulation. Moreover, returning these waste materials to circulation and producing new eco-friendly composites can reduce the number of landfills, the level of environmental pollution, and the use of synthetic materials made from fossil resources.

Recent advances review in tea waste: High-value applications, processing technology, and value-added products

Tea waste (TW) includes pruned tea tree branches, discarded summer and fall teas, buds and wastes from the tea making process, as well as residues remaining after tea preparation. Effective utilization and proper management of TW is essential to increase the economic value of the tea industry. Through effective utilization of tea waste, products such as activated carbon, biochar, composite membranes, and metal nanoparticle composites can be produced and successfully applied in the fields of fuel production, composting, preservation, and heavy metal adsorption. Comprehensive utilization of tea waste is an effective and sustainable strategy to improve the economic efficiency of the tea industry and can be applied in various fields such as energy production, energy storage and pharmaceuticals. This study reviews recent advances in the strategic utilization of TW, including its processing, conversion technologies and high value products obtained, provides insights into the potential applications of tea waste in the plant, animal and environmental sectors, summarizes the effective applications of tea waste for energy and environmental sustainability, and discusses the effectiveness, variability, advantages and disadvantages of different processing and thermochemical conversion technologies. In addition, the advantages and disadvantages of producing new products from tea wastes and their derivatives are analyzed, and recommendations for future development of high-value products to improve the efficiency and economic value of tea by-products are presented.

Molecular mechanisms of EGCG-CSH/n-HA/CMC in promoting osteogenic differentiation and macrophage polarization

2. This research investigates the impact of the EGCG-CSH/n-HA/CMC composite material on bone defect repair, emphasizing its influence on macrophage polarization and osteogenic differentiation of BMSCs. Comprehensive evaluations of the composite's physical and chemical characteristics were performed. BMSC response to the material was tested in vitro for proliferation, migration, and osteogenic potential. An SD rat model was employed for in vivo assessments of bone repair efficacy. Both transcriptional and proteomic analyses were utilized to delineate the mechanisms influencing macrophage behavior and stem cell differentiation. The material maintained excellent structural integrity and significantly promoted BMSC functions critical to bone healing. In vivo results confirmed accelerated bone repair, and molecular analysis highlighted the role of macrophage M2 polarization, particularly through changes in the SIRPA gene and protein expression. EGCG-CSH/n-HA/CMC plays a significant role in enhancing bone repair, with implications for macrophage and BMSC function. Our findings suggest that targeting SIRPA may offer new therapeutic opportunities for bone regeneration.

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.

Pruned tea biomass plays a significant role in functional food production: A review on characterization and comprehensive utilization of abandon-plucked fresh tea leaves

Tea is the second largest nonalcoholic beverage in the world due to its characteristic flavor and well-known functional properties in vitro and in vivo. Global tea production reaches 6.397 million tons in 2022 and continues to rise. Fresh tea leaves are mainly harvested in spring, whereas thousands of tons are discarded in summer and autumn. Herein, pruned tea biomass refers to abandon-plucked leaves being pruned in the non-plucking period, especially in summer and autumn. At present, no relevant concluding remarks have been made on this undervalued biomass. This review summarizes the seasonal differences of intrinsic metabolites and pays special attention to the most critical bioactive and flavor compounds, including polyphenols, theanine, and caffeine. Additionally, meaningful and profound methods to transform abandon-plucked fresh tea leaves into high-value products are reviewed. In summer and autumn, tea plants accumulate much more phenols than in spring, especially epigallocatechin gallate (galloyl catechin), anthocyanins (catechin derivatives), and proanthocyanidins (polymerized catechins). Vigorous carbon metabolism induced by high light intensity and temperature in summer and autumn also accumulates carbohydrates, such as soluble sugars and cellulose. The characteristics of abandon-plucked tea leaves make them not ideal raw materials for tea, but suitable for novel tea products like beverages and food ingredients using traditional or hybrid technologies such as enzymatic transformation, microbial fermentation, formula screening, and extraction, with the abundant polyphenols in summer and autumn tea serving as prominent flavor and bioactive contributors.

Valorization of tea waste: Composition, bioactivity, extraction methods, and utilization

Tea is the most consumed beverage worldwide and has many health effects. Although there are many different types of tea, black tea and green tea comprise 98% of total tea production in the world. Tea waste production consists of withering, crushing, fermentation, drying and finally packaging processes. All of the waste generated during this production line is called tea waste. Tea production results in a significant amount of waste that cannot be effectively used for value creation. This waste contains many different components including protein, fiber, caffeine, and polyphenols. Due to its rich composition, it can be revalorized for different purposes. In this study, the general composition and bioactive compounds of tea waste were reviewed. Despite the fact that there have been few studies on the bioactivity of tea waste, those studies have also been discussed. The extraction techniques that are used to separate the compounds in the waste are also covered. It has been indicated that these valuable compounds, which can be separated from tea wastes by extraction methods, have the potential to be used for different purposes, such as biogas production, functional foods, food additives, silages, soluble packaging materials, and adsorbents. Although there are some studies on the revalorization of tea waste, new studies on the extraction of bioactive compounds are necessary to improve its utilization potential.

Effects of Dietary Supplementation with Tea Residue on Growth Performance, Digestibility, and Diarrhea in Piglets

Thirty-six healthy 21-day-old weaned ternary piglets (Duroc × Landrace × Yorkshire) were randomly divided into two treatments with 18 replicates per treatment and one pig per replicate. The control group was fed with a basal diet and the test group was fed with diets supplemented with 1 kg/t tea residue. The test period was 28 days. The results are as follows: The addition of tea residue in the diet had no significant effect on the growth performance of weaned piglets (p > 0.05), but it could significantly reduce the diarrhea rate of piglets from 1 to 7 days and 1 to 28 days (p < 0.05). Compared with the control group, the dietary supplementation of tea residue had no significant effect on nutrient apparent digestibility, plasma biochemical indexes and plasma immune indexes (p > 0.05) but increased the content of glutathione in plasma (p < 0.05). Tea residue had no significant effect on the morphology of the jejunum and ileum of piglets (p > 0.05), but it could significantly reduce the content of chloride ions in feces (p < 0.05). Compared with the basal diet group, there was no significant difference in the relative expression of TMEM16A and CFTR mRNA in the colon of weaned piglets (p > 0.05). The whole-cell patch clamp recording showed that the TMEM16A and CFTR ion channels could be activated by ionomycin and forskolin, respectively. However, when HT-29 cells transfected with TMEM16A and CFTR channels were treated with tea residue extract, it could significantly inhibit the chloride current of the TMEM16A and CFTR ion channels (p < 0.05).

Valorization of biomass polyphenols as potential tyrosinase inhibitors

Tyrosinases (TYRs; EC 1.14.18.1) catalyze two sequential oxidative reactions of the melanin biosynthesis pathway and play an important role in mammalian pigmentation and enzymatic browning of fruit and vegetables. Inhibition of TYR activity is therefore an attractive target for new drugs and/or food ingredients. In addition, increasing evidence suggests that TYR regulation could be a novel target for treatments of cancer and Parkinson's disease. Biomasses, notably industrial byproducts and biowaste, are good sustainable sources of phytochemicals that may be valorized into bioactive compounds including TYR inhibitors. This review presents potential applications of biomass-derived polyphenols targeting TYR inhibition. Insights into structure-activity relationships of several polyphenols and their glycosides are highlighted. Finally, some remarks and perspectives on research into new TYR inhibitors from biomass waste are provided.

Valorization of protein-rich waste and its application

Energy shortages present significant challenges with the rising population and dramatic urbanization development. The effective utilization of high-value products generated from massive protein-rich waste has emerged as an excellent solution for mitigating the growing energy crisis. However, the traditional disposal and treatment of protein-rich waste, have been proven to be ineffective in resource utilization, which led to high chemical oxygen demand and water eutrophication. To effectively address this issue, hydrolysate and bioconversion products from protein-rich waste have been widely investigated. Herein, we aim to provide an overview of the valorization of protein-rich waste based on a comprehensive analysis of publicly available literature. Firstly, the sources of protein-rich waste with various quantities and qualities are systematically summarized. Then, we scrutinize and analyze the hydrolysis approaches of protein-rich waste and the versatile applications of hydrolyzed products. Moreover, the main factors influencing protein biotransformation and the applications of bioconversion products are covered and extensively discussed. Finally, the potential prospects and future directions for the valorization of protein-rich waste are proposed pertinently.

Extraction methods, physiological activities and high value applications of tea residue and its active components: a review

Tea is a traditional plant beverage originating from China as one of the most popular beverages worldwide, which has been an important companion in modern society. Nevertheless, as the waste after tea processing, tea residues from agriculture, industry and kitchen waste are discarded in large quantities, resulting in waste of resources and environmental pollution. In recent years, the comprehensive utilization of tea residue resources has attracted people's attention. The bioactive components remaining in tea residues demonstrate a variety of health benefits and can be recycled using advanced extraction processes. Furthermore, researchers have been devoted to converting tea residues into derivatives such as biosorbents, agricultural compost, and animal feeds through thermochemical techniques and biotechnology. This review summarized the chemical composition and physiological activities of bioactive components from tea residue. The extraction methods of bioactive components in tea residue were elucidated and the main high-value applications of tea residues were proposed. On this basis, the utilization of tea residues can be developed from a single way to a multi-channel or cascade way to improve its economic efficiency. Novel applications of tea residues in different fields, including food development, environmental remediation, energy production and composite materials, are of far-reaching significance. This review aims to provide new insights into developing the utilization of tea residue using a comprehensive strategy and exploring the mechanism of active components from tea residue on human health and their potential applications in different areas.HighlightsThe composition and function of tea residue active components were introduced.The extraction methods of active components from tea residue were proposed.The main high-value applications of tea residues were summarized.The current limitations and future directions of tea residue utilization were concluded.

Valorization of cocoa, tea and coffee processing by-products-wastes

The growing threat of food insecurity together with some challenges in demography, health, malnutrition, and income instability around the globe has led researchers to take sustainable solutions to ensure secure production and distribution of food. The last decades have been remarkable in the agri-food supply chain for many food industries. However, vast quantities of food by-products and wastes are generated each year. These products are generally disposed in the environment, which could have remarkable adverse effects on the environment and biodiversity. However, they contain significant quantities of bioactive, nutritional, antioxidative, and aroma compounds. Their sustainable use could meet the increased demand for value-added pharmaceutical, nutraceutical, and food products. The amount of agri-food wastes and their disposal in the environment are predicted to double in the next decade. The valorization of these by-products could effectively contribute to the manufacture of cheaper functional food ingredients and supplements while improving regional economy and food security and mitigating environmental pollution. The main aim of this chapter is to present an understanding of the valorization of the wastes and by-products from cacao, coffee and tea processing with a focus on their bioactive, nutritional, and antioxidant capacity.

Utilising Spent Tea Leaves Powder as Functional Ingredient to Enhance the Quality of Non-Gluten Shortbread Cookies

The increasing prevalence of gluten-related disorders has led to higher consumer demand for convenient, gluten-free bakery products with health-promoting properties. In this study, non-gluten shortbread cookies were incorporated with various kinds of spent (green, oolong, and black) tea leaves powder (STLP) at 8% w/w. Cookies with STLP had significantly higher (p < 0.05) moisture (2.18-2.35%), crude fibre (14.5-14.9%), total dietary fibre (22.38-22.59%), insoluble dietary fibre (15.32-15.83%), soluble dietary fibre (7.06-7.66%), and ash (1.9-2.0%) contents, but were significantly lower (p < 0.05) in carbohydrate (53.2-53.9%) and energy value (426.4-428.2 kcal) compared to control cookies (1.62%; 1.43%; 6.82%; 4.15%; 2.67%; 7.70%; 62.2%; and 457.8 kcal, respectively). The addition of STLP significantly enhanced (p < 0.05) the antioxidant properties of the cookies. Non-gluten shortbread cookies with spent green tea leaves powder (GTC) received the highest (p < 0.05) score for all sensory attributes, including overall acceptability. In addition, the shelf-life quality of the formulated cookie samples in terms of the moisture content, water activity, colour, texture, microbiology, and sensory properties was maintained (p > 0.05) for at least 22 days at 25 °C. STLP, which would have been previously thrown away, could be utilized as a potential functional ingredient to produce non-gluten shortbread cookies with enhanced nutritional, physicochemical, microbiological, sensory, and antioxidative properties.

Valorization of Food Waste to Produce Value-Added Products Based on Its Bioactive Compounds

The rapid growth of the global population and changes in lifestyle have led to a significant increase in food waste from various industrial, agricultural, and household sources. Nearly one-third of the food produced annually is wasted, resulting in severe resource depletion. Food waste contains rich organic matter, which, if not managed properly, can pose a serious threat to the environment and human health, making the proper disposal of food waste an urgent global issue. However, various types of food waste, such as waste from fruit, vegetables, grains, and other food production and processing, contain important bioactive compounds, such as polyphenols, dietary fiber, proteins, lipids, vitamins, organic acids, and minerals, some of which are found in greater quantities in the discarded parts than in the parts accepted by the market. These bioactive compounds offer the potential to convert food waste into value-added products, and fields including nutritional foods, bioplastics, bioenergy, biosurfactants, biofertilizers, and single cell proteins have welcomed food waste as a novel source. This review reveals the latest insights into the various sources of food waste and the potential of utilizing bioactive compounds to convert it into value-added products, thus enhancing people’s confidence in better utilizing and managing food waste.

Recent advances in biogas production using Agro-Industrial Waste: A comprehensive review outlook of Techno-Economic analysis

Agrowaste sources can be utilized to produce biogas by anaerobic digestion reaction. Fossil fuels have damaged the environment, while the biogas rectifies the issues related to the environment and climate change problems. Techno-economic analysis of biogas production is followed by nutrient recycling, reducing the greenhouse gas level, biorefinery purpose, and global warming effect. In addition, biogas production is mediated by different metabolic reactions, the usage of different microorganisms, purification process, upgrading process and removal of CO₂ from the gas mixture techniques. This review focuses on pre-treatment, usage of waste, production methods and application besides summarizing recent advancements in biogas production. Economical, technical, environmental properties and factors affecting biogas production as well as the future perspective of bioenergy are highlighted in the review. Among all agro-industrial wastes, sugarcane straw produced 94% of the biogas. In the future, to overcome all the problems related to biogas production and modify the production process.

Enhanced biogas production from food waste and activated sludge using advanced techniques - A review

Biogas generation using food waste anaerobic co-digestion with activated sludge provides a cleaner addressable system, an excellent solution to global challenges, the increasing energy demands, fuel charges, pollution and wastewater treatment. Regardless of the anaerobic digestate end product values, the technology lacks efficiency and process instability due to substrate irregularities. Process parameters and substrate composition, play a vital role in the efficiency and outcome of the system. Intrinsic biochar properties such as pore size, specific surface properties and cation exchange capacity make it an ideal additive that enriches microbial functions and enhances anaerobic digestion. The pretreatment and co-digestion of food waste and activated sludge are found to be significant for efficient biogas generation. The advantages, drawbacks, limitations, and technical improvements are covered extensively in the present review besides the recent advancement in the anaerobic digestion system.

Improved performance and microbial community dynamics in anaerobic fermentation of triticale silages at different stages

Production of high-quality grass-based silages by microbial-mediated anaerobic fermentation is an effective strategy in livestock farms. In the present study, an ensiling process was used to preserve and enhance fermentative metabolites in triticale silages with novel inoculants of Lactobacillus rhamanosus -52 and, Lactobacillus rhamanosus-54. Triticale silages treated with LAB predominantly had lower pH values than control silages due to rapid changes of microbial counts. LAB addition improved anaerobic fermentation profiles showing higher lactic acid, but lower acetic acid and butyric acid concentrations. A background microbial dynamic study indicated that the addition of L. rhamanosus-52 and L. rhamanosus-54 improved silage fermentation, enriched Lactobacillus spp., and decreased microbial richness with diversity, leading to increased efficiency of lactic acid fermentation. In conclusion, LAB treatment can increase silage quality by enhancing the dominance of desirable Lactobacillus while inhibiting the growth of undesirable microbes.