Tea is the second most commonly drunk beverage in the entire world, after water. The UK drinks an estimated 165 million cups of tea every day, or enough tea to fill eight Olympic swimming pools. Tea leaves, the raw component of black tea, contain many phenolic and polyphenolic compounds including flavanols, flavones and theaflavins, which have intrinsic antioxidant activity. Antioxidants function as scavenger molecules in the bloodstream, absorbing reactive oxygen species and free radicals, which cause oxidative stress on cells and biological processes.
Evidence suggests that the Consumption of tea increases antioxidant levels in humans. Studies on the antioxidant and antimicrobial potentials of tea extract chemicals have been undertaken, with positive results. The polyphenols in tea display an inhibition of growth in gram-positive and negative bacteria, as well as other microorganisms. There is evidence to suggest that catechins in tea extracts can work in tandem with β-lactam antibiotics (such as penicillin) to improve efficacy. Tea extracts have become an expanding commodity chemical for their reported therapeutic effects. It has been proposed that tea extracts could be used as preservatives for foods, allowing them to stave off bacterial growth for longer using a safe and non-toxic method.
Studies have indicated that waste from tea production is also rich in these phenolic compounds and can be extracted in useful quantities from the solid waste, which is often left to decompose in landfill sites at tea production facilities.
5.89 million tonnes of tea were produced in 2018, creating an estimated 120,000 tonnes of solid tea waste during production. The global demand for tea is rising and to meet this demand more waste will be produced. Tea waste, untreated, is unsuitable for direct land application as the caffeine and tannic acid content can lower fragile soil pH levels. Likewise, the caffeine and tannic acid content of tea waste can make it harmful to be supplied as animal feed. This means that chemical treatment is required before repurposing tea waste as compost or animal feed.
Caffeine and polyphenols can be extracted from waste tea easily and cost-effectively. A substantial quotient of polyphenols can be recovered using ethanol as a solvent. Ethanol is a more sustainable solvent than traditional extraction solvents and can be sourced easily from biomass. Other methods, such as utilising carbon dioxide in its super-critical liquid state is also a popular, new green solvent method which can be fine tuned to selectively extract desired materials.
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