molecules Article Influence of Tea Brewing Parameters on the Antioxidant Potential of Infusions and Extracts Depending on the Degree of Processing of the Leaves of Camellia sinensis Jolanta Kowalska 1, *, Agata Marzec 1 , Ewa Domian 1 , Sabina Galus 1, * , Agnieszka Ciurzy ´ nska 1 , Rita Brzezi ´ nska 2 and Hanna Kowalska 1, *   Citation: Kowalska, J.; Marzec, A.; Domian, E.; Galus, S.; Ciurzy ´ nska, A.; Brzezi ´ nska, R.; Kowalska, H. Influence of Tea Brewing Parameters on the Antioxidant Potential of Infusions and Extracts Depending on the Degree of Processing of the Leaves of Camellia sinensis. Molecules 2021, 26, 4773. https://doi.org/ 10.3390/molecules26164773 Academic Editors: Academic Editors: Daniel Rico and Francesco Cacciola Received: 17 June 2021 Accepted: 3 August 2021 Published: 6 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Food Engineering and Process Management, Institute of Food Sciences, Warsaw University of Life Sciences, 159c Nowoursynowska St., 02-776 Warsaw, Poland; agata_marzec@sggw.edu.pl (A.M.); ewa_domian@sggw.edu.pl (E.D.); agnieszka_ciurzynska@sggw.edu.pl (A.C.) 2 Department of Chemistry, Institute of Food Sciences, Warsaw University of Life Sciences, 159c Nowoursynowska St., 02-776 Warsaw, Poland; rita_glowacka@sggw.edu.pl * Correspondence: jolanta_kowalska@sggw.edu.pl (J.K.); sabina_galus@sggw.edu.pl (S.G.); hanna_kowalska@sggw.edu.pl (H.K.); Tel.: +48-22-59-37679 (J.K.); +48-22-59-37565 (S.G.); +48-22-59-37579 (H.K.) Abstract: The polyphenol content of tea depends on the growing region, harvest date, the production process used, and the brewing parameters. In this study, research was undertaken that included an analysis of the influence of the brewing process parameters on the content of total polyphenols (Folin-Ciocalteu), epigallocatechin gallate (HPLC), and antioxidant activity (against DPPH radicals) of fresh tea shrub leaves grown from Taiwan and of teas obtained from them (oolong, green in bags, and green loose from the spring and autumn harvest). The antioxidant potential was determined in the methanol and aqueous extracts, as well as in infusions that were obtained by using water at 65 or 100 ◦ C and infusing the tea for 5 or 10 min. The highest content of total polyphenols and epigallocatechin gallate was found in green tea extracts from the spring harvest. However, in the case of infusions, the highest content of these compounds was found in green tea in bags. Steaming at 100 ◦ C for 10 min, turned out to be the most favourable condition for the extraction. Oolong tea, brewed at 100 ◦ C for 5 min was characterised by the highest antioxidant activity against stable DPPH radicals. Keywords: tea; brewing tea; phenolic compounds; antioxidants; epigallocatechin-3-gallate 1. Introduction Tea is one of the most consumed beverages [1]. Beneficial effects on the circulatory sys- tem, improvement of heart function, prevention of atherosclerosis and obesity, anticancer, anti-inflammatory, and antibacterial properties are some of the properties of tea [2,3]. Most of them result from the presence of biologically active substances in tea leaves, mainly polyphenolic compounds, but also alkaloids (theobromine, theophylline, and caffeine) and theanine [4,5]. Tea bushes are grown mainly in Southeast Asia (China, Japan, India, Sri Lanka, Taiwan, Malaysia) but also in South America (Argentina and Brazil), Africa (Kenya), and South Africa. The amount of harvest each year in each region depends on the climate. It is believed that early harvest is better, and the tea obtained from it has better organoleptic and health-promoting qualities [6]. Moreover, the location of the plantations depending on the height above sea level has an impact on the cultivation of tea bushes. The higher it is, the better the properties of the tea. Tea is divided into three types resulting from the level of fermentation: green tea, oolong tea, and black tea [3,7]. The polyphenol content of tea depends on the growing conditions and the method of leaf processing. The dominant polyphenols in tea are catechins, which constitute Molecules 2021, 26, 4773. https://doi.org/10.3390/molecules26164773 https://www.mdpi.com/journal/molecules