Effects of Microwave-Assisted Extraction Conditions on Antioxidant Capacity of Sweet Tea (Lithocarpus polystachyus Rehd.)

Abstract

In this study, the effects of microwave-assisted extraction conditions on antioxidant capacity of sweet tea (Lithocarpus polystachyus Rehd.) were studied and the antioxidants in the extract were identified. The influences of ethanol concentration, solvent-to-sample ratio, microwave power, extraction temperature and extraction time on Trolox equivalent antioxidant capacity (TEAC) value, ferric reducing antioxidant power (FRAP) value and total phenolic content (TPC) were investigated by single-factor experiments. The response surface methodology (RSM) was used to study the interaction of three parameters which had significant influences on antioxidant capacity including ethanol concentration, solvent-to-sample ratio and extraction time. The optimal conditions for the extraction of antioxidants from sweet tea were found as follows—ethanol concentration of 58.43% (v/v), solvent-to-sample ratio of 35.39:1 mL/g, extraction time of 25.26 min, extraction temperature of 50 ℃ and microwave power of 600 W. The FRAP, TEAC and TPC values of the extract under the optimal conditions were 381.29 ± 4.42 μM Fe(II)/g dry weight (DW), 613.11 ± 9.32 μM Trolox/g DW and 135.94 ± 0.52 mg gallic acid equivalent (GAE)/g DW, respectively. In addition, the major antioxidant components in the extract were detected by high-performance liquid chromatography with diode array detection (HPLC-DAD), including phlorizin, phloretin and trilobatin. The crude extract could be used as food additives or developed into functional food for the prevention and management of oxidative stress-related diseases.

Influences of Microwave-Assisted Extraction Parameters on Antioxidant Activity of the Extract from Akebia trifoliata Peels

“…The TEAC and TPC values also increased continuously from 300 to 500 W, and then reduced slowly. The changing trends of three parameters of Akebia trifoliate peel extract were also in agreement with those reported in a previous paper [ 10 ]. MAE is based on heating the sample by utilizing microwave energy.…”

“…Microwave radiation could destroy cell structure so that the active compound could dissolve into the sample [ 13 ]. With the rise of microwave power, the interaction between the sample molecules and the electromagnetic field was enhanced, and the recovery efficiency was improved [ 10 ]. However, higher microwave power might result in thermal degradation and deterioration of some active components [ 19 ].…”

“…Theoretically, RSM can be applied for optimizing all input variables. Actually, three parameters were usually selected to study interactions in the literature [ 10 ], which are often enough, and more parameters are not necessary, and even waste time, cost and labor. Thus, in this study, three parameters showing the strongest effects, including ethanol concentration, solvent-to-material ratio and extraction time, were chosen to test their interactions for extraction of antioxidants from Akebia trifoliate peel in the RSM design by Design Expert 11 (Stat-Ease Inc., Minneapolis, MN, USA).…”

“…The extraction of antioxidants from plant materials could be carried out using different methods, including traditional techniques such as reflux, percolation, soaking, maceration and Soxhlet extraction, and new extraction methods such as enzyme-assisted extraction, ultrasound-assisted extraction and microwave-assisted extraction (MAE) [ 6 , 7 , 8 , 9 , 10 ]. Taking into account the consumption of organic solvent, extraction time, cost and efficiency, MAE is an advanced method with many advantages [ 10 ]. The electromagnetic field generated by microwave radiation could accelerate the movement of molecules, resulting in a rapid extraction [ 11 ].…”

Optimizing Conditions for Microwave-Assisted Extraction of Polyphenolic Content and Antioxidant Activity of Barleria lupulina Lindl.

“…Ethanol has several advantages over other solvents, such as higher extraction ability, environmental compatibility, lower toxicity, and cost, and it is the most commonly used solvent in the extraction of phytochemicals from plant extracts [ 30 , 43 ]. Ethanol concentrations in water have been reported to have significant effects on plant extraction quality [ 44 , 45 ]. In the present study, B. lupulina Lindl.…”