Effects of Different Harvesting Times and Oxidative Fermentation Methods on Phytochemicals, Flavors, and Sensory Properties of Korean Teas

Tea (Camellia sinensis) is one of the most popular beverages consumed worldwide. In Korea, teas made with C. sinensis leaves are historically regarded as both spiritual and healthy. As such, the increasing popularity of tea in Korea can partly be attributed to a trend toward leading a healthy lifestyle. An important factor that directly impacts the overall quality and health benefits of tea is the degree of fermentation. It is important to understand the changes occurring during oxidative fermentation because the process vastly changes the chemical and physical compositions of teas. However, most studies on this topic have been conducted using teas post-fermentation and thus do not provide precise processing information. Moreover, while numerous studies have been conducted to investigate health-promoting compounds in tea, limited information is available regarding the physicochemical differences between teas harvested at different times. Such information would likely be valuable to consumers who mainly drink tea for its health benefits. Thus, the present studies were conducted to investigate two topics: how tea processing (oxidative fermentation) influences the phytochemical compositions including polyphenolics and volatile compounds; and how tea harvesting time affects the physicochemical composition of green teas and sensorial properties. The first study was conducted by controlling the degree of oxidative fermentation of the tea leaves as processed within a precise fermentation environment. The teas used for the second study were obtained from a reliable local tea store that issued a certificate of harvesting time and growing region information. The catechin concentration was higher in green tea with 0% fermentation since the catechins were transformed into theaflavin, which resulted in decreased antioxidant capacity due to lowered concentrations of polyphenolic compounds. Overall, early harvested green teas had higher antioxidant capacities, likely due to high polyphenolic contents composed mostly of catechins. Unfortunately, the caffeine concentration negatively impacted the sensorial property due to its intense bitterness and astringency. Volatile compounds including linalool, 2,3-methyl butanal, 2-heptanone, and (E,E)-3,5-Octadien-2-one were also related to consumer approval of the green teas. The results obtained from this study could be useful to tea manufacturers as well as beverage developers aiming to increase the antioxidative properties of their products.