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HPLC analysis of polyphenols and methylxanthines and antioxidant properties of conventionally and high hydrostatic pressure (HHP) extracted teas

Upon modern consumers’ demands for higher intake of bioactive/functional compounds in daily diet, consumption of Camellia sinensis products, including tea, arises, due to its pleasant aroma and numerous health-promoting properties, attributed to the presence of phytochemicals, primarily catechins and catechin-gallates as representatives of polyphenols, and caffeine among methylxanthines. There is currently an increasing interest in innovative extraction techniques such as Microwave-Assisted Extraction (MAE), Ultrasonic-Assisted Extraction (UAE) and High Hydrostatic Pressure (HHP) that enable fast and efficient extraction of phytochemicals as functional ingredients from various plant matrixes. As opposed to previously employed techniques for the extraction of polyphenols from tea, HHP extraction can be operated at room temperature, avoiding the use of high temperatures that can deteriorate thermo-sensitive ingredients and result with loss of their biological activities. Therefore, the aim of this study was to compare the extraction efficiency of polyphenols and methylxanthines from four different types of teas (white, green, oolong and black teas), by employing conventional and HHP extraction using water and hydro-alcoholic mixture as the extraction solvents. The content of total polyphenols was determined spectrophotometrically, individual polyphenols and methylxanthines were determined by means of high performance liquid chromatography (HPLC) analysis, while 2, 2-diphenyl-1-picrylhydrazyl (DPPH) and 2, 2’-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) assays were used to assess the antioxidant capacity of tea extracts. Green tea generally exhibited the highest content of total and individual polyphenolic compounds, as well as the antioxidant capacity, among all investigated teas. The combination of conventional extraction using 50% ethanol (v/v) as the extraction solvent at 100°C and stirring for 10 min was the most efficient for extraction of polyphenols from teas. Flavan-3-ols were the prevalent group of polyphenols, with epigallocatechin gallate being the most abundant compound (ranging from 43.14 to 2885.50 mg/L), followed by caffeine (ranging from 98.27 to 1895.97 mg/L) among methylxanthines. In comparison to conventional extraction, high hydrostatic pressure provided lower extraction yield of bioactive compounds, regardless of the type of tea or extraction solvent, indicating that the use of higher temperature is the determining parameter for the extraction of bioactive compounds from teas.

Camelia sinensis ; extraction ; high hydrostatic pressure ; methylxanthines ; polyphenols

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