Green approach for polyphenol extraction from waste tea biomass: Single and hybrid application of conventional and ultrasound-assisted extraction.

Based on a green approach, the potential use of waste tea biomass (fiber and second sieving) with rich polyphenol content was investigated as an alternative source of polyphenol to achieve an economic added value. In addition, this study demonstrated a comparative approach to explore the most sustainable green extraction method by the assessment of single ultrasound-assisted extraction (UAE) at various frequencies (20, 35, and 200 kHz) and the hybrid operations of ultrasound (US) and thermal extraction (50 °C and 80 °C). As a result, it has been determined that waste tea biomass, with a polyphenol extraction rate of more than 80%, provides a higher recovery capacity than tea leaf (the highest polyphenol recovery rate of 72.5%) in almost all single operations. Among the single UAE, 20 kHz was expressed as the method succeeding with high recovery rates (84%) within 30 min for fiber waste. In contrast, the hybrid operation consisting of 20 kHz US (20 min) with heating at 80 °C (10 min) yielded the highest extraction efficiency with 92% in the same time interval more economically for second sieving waste tea biomass. Therefore, this study has shown that it is possible to utilize UAE alone or in combination with heat extraction from tea waste for environmentally friendly, rapid, and effective polyphenol extraction.