Recycling of Tea Waste: Simple and Effective Separation of Caffeine and Catechins by Microwave Assisted Extraction (MAE)

Abstract

This study was designed to develop a cost effective green extraction method to separate valuable chemicals from black tea waste (BTW) and tea dust called "caffeine dust" (CD). These materials are totally unwanted residue and treated as rubbish. Two extraction methods were used for extraction of waste materials obtained in three collection periods. In conventional extraction method, material was subjected to hot water extraction at 80 o C for 40 minutes. In microwave assisted extraction (MAE) method, different eco-friendly aqueous solvents (water, citric acid-water or ethanol-water) were used under a controlled 600 W microwave power at 80 o C for only 4 minutes treatment in a close microwave system. MAE and conventional method gave similar extract yields for both waste materials but MAE was more successful and economical completing the extraction in shorter time. Using citric acid-water solvent in MAE significantly increased the extraction of individual catechins such as epicatechin (EC) and epigallocatechin gallate (EGCG). This study showed that tea waste could be utilized for production of valuable chemicals using nontoxic solvents at extremely short extraction periods.

Introductory Chapter: From Waste to New Resources

“…Polysaccharide/dietary fibers Fruits pomace, sugar beet, sunflower heads Solid-liquid extraction [13] Citrus peel and apple pomace Subcritical water extraction [14] Cereal by-products Enzymatic treatment and sequential extraction [15] Apple pomace Hot-compressed water [16] Organic acids [17] Olive mill wastewaters Ultrafiltration and nanofiltration [18] Rice bran Microwave treatment and microbial fermentation [19] Phenolic compounds Apple pomace Microwave-assisted extraction [20] Electric field-assisted extraction [21] Tomato pomace and skin Enzymatic-assisted extraction/solvent extraction [22] Potato peels Microwave-assisted extraction [23] Olive cake Ultrasound-assisted extraction [24] Avocado peel and seeds Solvent extraction [25] Wheat beans Ultrasound-assisted extraction [26] Tea by-products Supercritical fluid extraction; microwave-assisted extraction/solvent extraction [27,28] Bran and germs Ultrasound-assisted extraction [29] Grape by-products Ultrafiltration [30] High-voltage electrical discharges and ultrafiltration [31] Supercritical fluid extraction [32] Solvent extraction/microwave-assisted extraction/ultrasound-assisted extraction [33] Blueberry residue Supercritical fluid extraction and pressurized liquids [34] Flax seeds Solid-liquid extraction [35] Introductory Chapter: From Waste to New Resources DOI: http://dx.doi.org/10.5772/intechopen.89442…”

“…Tea waste Microwave-assisted extraction/solvent extraction [28] Oils Rice bran Supercritical carbon dioxide extraction and compressed liquefied petroleum gas/solid-liquid extraction [36,37] Essential oils Citrus peel Solvent extraction/hydrodistillation [38] Steam explosion at high temperature and pressure [39] Microwave-assisted hydro-diffusion [40] Proteins Brewers' spent grain Sequential extraction of proteins and arabinoxylans; enzymatic-assisted extraction [15,41] Rice by-products Enzymatic hydrolysis and membrane filtration technique [42] Hazelnut meal Solvent extraction (water, acetone) [43] Rapeseed by-products Ultrasound-assisted aqueous extraction [44] Carotenoids Tomato pomace and skin Enzymatic-assisted extraction [45] Supercritical fluid extraction/solvent extraction [46] Supercritical fluid extraction [47] Citrus peel Ultrasound-assisted extraction [48] Sea buckthorn seeds Supercritical carbon dioxide fluid extraction [49] Proteins and bioactive peptides Whey wastewater Membrane separation/ultrafiltration/microfiltration/nanofiltration/reverse osmoses [50] Mild enzymatic hydrolysis [51] Cheese whey Ultrafiltration/nanofiltration [52] Fish and chicken Isoelectric solubilization and precipitation [53] Sardine solid waste Enzymatic hydrolysis and ultrafiltration [54] Shellfish Enzymatic hydrolysis and micro-, ultra-, and nanofiltration/ion exchange chromatography [55] Sugars Whey wastewater Membrane separation and spray drying [50] Cheese whey Ultrafiltration/nanofiltration [52] satisfy the current demands of economic preservation and consumer satisfaction in safety, nutritional and sensory aspects. Also, as the preservation of foods is often a multicomponent issue, the "hurdle" concept was introduced, highlighting the complex interaction between the factors that are significant for food safety and stability [56][57][58].…”

Sequential Green Extraction of Caffeine and Catechins from Green Tea

“…Extraction time and microwave power from MAE parameters can influence the extraction performance [24]. Extraction conditions were previously reported by our group [22,23]. 10 g of tea sample and 200 ml ethanol-water (1:1 v/v) solution were placed in extraction vessel.…”

“…MAE is an effective extraction process for green tea which was previously utilised for extraction of various tea samples (dried, fresh or frozen) collected in first, second and third collection periods [22,23]. MAE provides a mixture of both caffeine and catechins and another separation step should be employed for effective separation of caffeine from catechins.…”

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“…Flavonoids Apple pomace, Citrus peels and seeds Solid-liquid extraction [105,108] Pectin Apple pomace, citrus peels, fruit wastes (peels and pomace) Solid-liquid extraction, Microwave-assisted extraction [105,109] Dietary fibers Apple pomace, industrial onion waste Solid-liquid extraction [110,111] Anthocyanins Grape skins, grape peels Ultrasonication, high hydrostatic pressure and pulsed electric field, superheated liquid extraction [112][113][114][115][116] Phenolic compounds Apple pomace, peach pomace, grape skins, grape seeds Supercritical fluid extraction, solid-liquid extraction, microwave-assisted extraction, ultrasonication [117][118][119][120] Caffeine Green tea leaves Microwave-assisted extraction, supercritical fluid extraction [121][122][123][124] β-carotene and lycopene Tomato paste waste, tomato peels Microwave-assisted extraction, supercritical fluid extraction [125][126][127] Fruits and vegetables are generally the most widely investigated substrates for the extraction of phenolic compounds and other bioactive components such as proteins, dietary fibers (Table 4).…”