Ultrasonic-assisted and enzymatic-assisted extraction to recover tannins, flavonoids, and terpenoids from used tea leaves using natural deep eutectic solvents

Abstract

The conventional extraction technique using organic solvent was employed to recover bioactive compounds from plants; however, this technique showed low efficiency and caused environmental pollution. Novel extraction techniques such as ultrasound-assisted extraction (UAE) and enzymatic-assisted extraction (EAE) combined with natural deep eutectic solvent were developed to overcome this problem. The efficiency of a binary NADES system with sonication was evaluated based on total tannin contents (TTAC), total flavonoid content (TFC), and total terpenoid content (TTC). The NADES system with a molar ratio of acetic acid and glycerol at 2:1 showed the highest TTAC and TFC, while acetic acid and glucose at 2:1 yielded the highest TTC. The impact of UAE and EAE parameters on extraction yield was examined. Combined methods, including ultrasonic-enzymatic assisted extraction (UEAE), enzymatic-ultrasonic assisted extraction (EUAE), and simultaneous ultrasonic-enzymatic assisted extraction (SUEAE), were performed using NADES. UEAE exhibited the highest extraction yield and biological activities. Scanning electron microscopy (SEM) was employed to examine the surface variations of used tea leaves before and after treatment. This study demonstrated that UEAE is a sustainable technique for recovering valuable compounds from used tea leaves.