Evaluation of extraction method on antioxidant activity of mountain tea (Stachys lavandulifolia V.) extract and optimization condition of encapsulated extract production

In this study, extracts of mountain tea were obtained by maceration, supercritical fluid, ultrasound assisted, subcritical water and microwave. The highest extraction efficiency (22.55%) and total phenolic content (80.50 mg GA/g DM) was observed in extract obtained via ultrasound assisted extraction. Antioxidant activity of different concentrations of extracts was compared with 100 ppm TBHQ synthetic antioxidant and an increased in concentration of extract increased antioxidant activity. Type and percentage of wall materials (0, 50 and 100), the ratio of extracts to wall materials (0.1, 0.25 and 0.4 w/w), and sonication time (2, 4 and 6 min) as independent variable levels and encapsulation efficiency of phenolic compounds, particle size of nanocapsule and zeta potential were considered as a response to optimization of encapsulation conditions of the extract. An increase in sonication time resulted in increased encapsulation efficiency and decreased particle size of capsule. As the ratio of extract to wall materials increased, the encapsulation efficiency of extract increased and particle size decreased. Type of wall materials has effect on encapsulation efficacy, zeta potential, and particle size of capsule.  The optimum conditions for encapsulating of mountain tea extract were 6 min ultrasound; the ratio of extract to wall 0.4 and the amount of Arabic gum and alginate were 30.3% and 69.7% respectively. In optimum conditions, the encapsulation efficiency, Zeta potential and particle size were 57.43%, -52.1 mV and 82.06 nm. The amount of sedimentation and release of extract during the storage period was increasing. Nanocapsule has a smooth and interconnected structural that due to high encapsulation efficiency this nanocapsule can be added to food as an antioxidant compound.