Abstract
In this study, the feasibility of improving the extraction yield of green tea antioxidant polyphenols by the combination of ultrasound-assisted extraction (UAE) and deep eutectic solvents (DESs) was investigated. Choline chloride (ChCl)-glycerol was selected as the best DES among 12 ChCl-based DESs to extract tea antioxidant polyphenols. Subsequently, the influences of extraction parameters on total phenolic content (TPC) values were investigated, and liquid/solid ratio, ultrasonic power, and ultrasonic time were optimized based on the response surface methodology. The optimal extraction conditions were a liquid to solid ratio of 36:1 (mL/g), ultrasonic power of 461.5 W, and ultrasonic time of 21 min, with the highest TPC value of 243 ± 7 mg gallic acid equivalent (mg GAE)/g dry weight (DW), which was 13% higher than that before optimization. In addition, under the optimal extraction conditions, tea polyphenolic extract exhibited higher antioxidant activity compared with conventional extraction methods. Four major catechins in the green tea extracts, including (−)-epicatechin (EC), (−)-epigallocatechin (EGC), (−)-epicatechin gallate (ECG) and (−)-epigallocatechin gallate (EGCG) were identified and quantified by high-performance liquid chromatography. In addition, scanning electron microscopy (SEM) analysis revealed that UAE-DES effectively disrupted the green tea leaf cells, thereby improving tea polyphenol yield. In summary, UAE-DES is an ideal green extraction method for the extraction of tea antioxidant polyphenols.
Highlights
The tea plant (Camellia sinensis) is cultivated in many countries, such as China andJapan, and tea has become a universally consumed beverage around the world [1]
The effects of extraction parameters on the total phenolic content (TPC) of green tea extracts were investigated by using single-factor experiments, including the liquid to solid ratio (10:1, 20:1, 30:1, 40:1, and 50:1), Choline chloride (ChCl)/glycerol molar ratio (1:4, 1:3, 1:2, 1:1, and 2:1), water content in deep eutectic solvents (DESs)-1
It was significant that the TPC values in the group of ChCl-sugar, and ChCl-sugar-derived polyols
Summary
The tea plant (Camellia sinensis) is cultivated in many countries, such as China andJapan, and tea has become a universally consumed beverage around the world [1]. Antioxidants 2020, 9, 785 the simplest manufacturing process but the most excellent benefits, and tea antioxidant polyphenols (TPs) constitute the majority of advantageous components in green tea [2]. Catechins are the principal components of tea antioxidant polyphenols, which mainly include two non-ester catechins,. (−)-epicatechin (EC) and (−)-epigallocatechin (EGC), and two ester catechins, (−)-epicatechin gallate (ECG) and (−)-epigallocatechin gallate (EGCG) [3,4]. These catechins show potential health benefits, such as anticancer, anti-obesity, antibacterial, antioxidant, and antiviral effects [5,6,7,8]. It is of great importance to establish an eco-friendly and efficient extraction method for extracting antioxidant polyphenols in green tea
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