A comparative study of ultra-sonication and agitation extraction techniques on bioactive metabolites of green tea extract

•Agitation and sonication techniques increased the yields of green tea metabolites.•Agitation and sonication showed similar extraction efficiencies of metabolites.•Antioxidant activities of green tea extracts were increased by both techniques.•Both techniques can be used to produce antioxidant-rich green tea extract. The aim of this study was to compare methods for efficient extraction of green tea metabolites. Aqueous green tea leaf powder extracts were prepared by ultra-sonication extraction (UE), agitation extraction (AE), and the conventional extraction method (control) at different temperatures (60, 70, and 80 °C) and times (5–30 min). Compared to the control, both UE and AE techniques significantly increased the yields of polyphenols (three-fold), catechins (two-fold), and flavonoids (two-fold), and resulted in higher antioxidant activity. For both techniques, highest extraction efficiency of bioactive metabolites occurred at 80 °C for 20 min. Caffeine, total free amino acid, vitamin C, and total soluble solid contents were also significantly increased using either technique compared to the control. Thus, AE and UE have similar extraction efficiencies and could be used to prepare antioxidant-rich green tea extract or green tea extract powder.