Changes in Phytochemicals and Determination of Optimum Fermentation Time during Black Tea Manufacturing

Abstract

Black tea processing consists of four steps, namely withering, CTC, fermentation and drying, while cup quality made tea mostly controlled by fermentation step. This study evaluated biochemical changes at different stages of black tea processing in Bangladesh and determined the optimum fermentation time. Samples were collected from different tea processing stages to measure major phytochemicals and time intervals during fermentation to measure theaflavins and thearubigins ratio. Caffeine content was the least susceptible to processing steps. Biochemical changes started at withering, cell maceration and enzymatic oxidation started at CTC processing, thus the major reduction in the reducing sugar (20.46 to 04.95 ppm), catechin (16.88 to 7.95 ppm) and polyphenol (42.30 to 30.73 ppm) occurred here. The significant changes appeared during fermentation when polyphenol content decreased from 44.66 to 18.23 and catechin from 17.41 to 03.98 ppm due to the breakdown of these compounds to theaflavins (TF) and thearubigins (TR). The TF and TR ratio increased with fermentation time, and the highest of 1:8.4 was found at 50 min, which turned into 1:10 in the final product. The made tea quality parameters were comparable or better at fermentation time of 50 min than the quality of the black tea available in market.

Processing, chemical signature and food industry applications of Camellia sinensis teas: An overview

“…Bioactive compounds are sensitive to oxidation, hydrolysis, and other chemical reactions. These reactions occur during processing, where part of the compounds are oxidized ( Paiva et al, 2021 , Rahman et al, 2020 ), and after drinking the infusion, where gastrointestinal digestion can change chemical structures, resulting in compounds with different bioactivities ( Jilani et al, 2015 , Ribeiro et al, 2021 ). In order to increase the stability of phenolic compounds and take advantage of their bioactive properties, technologies have been developed for several different industrial areas ( Jilani et al, 2020 , Ribeiro et al, 2019 , Silva et al, 2021 ).…”

“…The withering step aims to reduce the moisture in the tea leaves, making them soft and leathery ( Rahman et al, 2020 ) and to modify sensory characteristics of teas such as taste and aroma. During this step, the phenolic profile is modified, especially in flavan-3-ols, predominantly epicatechins (90%), which represent between 60 and 70% of the total phenolic compounds ( Paiva et al, 2021 ).…”

“…Withering reduces the concentration of reducing sugars and increases the concentration of caffeine in tea, as well as oxidase enzymes. The polyphenol oxidase (PPO) and peroxidase (POD) enzymes play an important role in tea processing since catalyze the oxidation reactions of phenolic compounds ( Rahman et al, 2020 ). Yılmaz, Özdemir, and Gökmen (2020) demonstrated that the total free amino acid content of teas increased in the withering stage while decreasing in the drying stage, proving that different stages of tea processing affect the level of GABA (Gamma-aminobutyric acid), kynurenic acid, and dopamine.…”

“…Fermentation, in this case, refers to an enzyme-catalyzed oxidative process, without the involvement of microbiological agents ( Salman et al, 2021 ). At this stage, important biochemical changes occur, such as the oxidation of phenolic compounds, resulting in the appearance of theaflavins and thearubigins ( Rahman et al, 2020 ). Theaflavins, formed by the condensation of orthoquinones from the oxidation of catechins, are responsible for the beverage's brightness and liveliness.…”

“…Theaflavins, formed by the condensation of orthoquinones from the oxidation of catechins, are responsible for the beverage's brightness and liveliness. On the other hand, thearubigins, a product of the oxidation of gallic acids, which form polymerized epitheaflavic acids, characterize the infusion's color, flavor and body ( Rahman et al, 2020 ). Fermented teas differ in fermentation time and can be classified as short fermentation (oolong tea), full fermentation (black tea) and fermented after processing (pu-ehr tea) ( Fig.…”