Microwave-assisted extraction of major components in tea residues

Abstract

Tea contains several-health benefit components (e.g., polyphenols and caffeine). General tea brewing condition (80-90 ^oC, 2-3 mins) is too short to extract all polyphenols and other major components in tea. Microwave was found to help accelerate the tea extraction process. Thus, this study aimed to determine the amount of the major components (e.g. polyphenol and caffeine) in tea residues (i.e., green tea and oolong tea) by using Microwave-Assisted Extraction (MAE) method and investigate its antioxidant capacities (DPPH-Radical scavenging activity (DPPH) and the ferric reducing antioxidant power (FRAP)). In addition, the effect of additive concentrations (citric acid and ascorbic acid: 0.2, 0.4, 0.6, 0.8 %w/v) on the efficacy of tea residues extraction was also examined. The results showed that the MAE with 0.8%w/v ascorbic acid extraction condition of green tea residues yielded the higher amount of total polyphenols content (TPC) and DPPH radical scavenging activity (81.26 mg gallic acid equivalent (GAE)/100 g dried weight (DW) and 98.14%, respectively ) than other extraction conditions. While FRAP capacity of acid added MAE extraction of green tea residues was lower than that of MAE only extraction condition. In addition, the caffeine content, obtained from the MAE with 0.8% w/v ascorbic acid extraction condition of oolong tea residues, was high (70.94% extract). Therefore, MAE with acids could help maximize the extraction of the total polyphenols content, caffeine content and DPPH radical scavenging activity from tea residues.