J Food Process Preserv. 2019;43:e14283. wileyonlinelibrary.com/journal/jfpp | 1 of 10 https://doi.org/10.1111/jfpp.14283 © 2019 Wiley Periodicals, Inc. 1 | INTRODUCTION Tea is made from young shoots of the plant Camellia sinensis. Processing steps in black tea manufacturing are withering, macera‐ tion, fermentation (oxidation), and drying. Generally, two leaves and a bud are used for processing of tea. Total polyphenol content in green tea shoots is 25%–30% of dry solids (Tanaka, Tsai, & Wang, 2009). Fresh leaves are withered for 14–16 hr where leaves are con‐ ditioned physically, as well as chemically for subsequent processing stages. Withered leaves are macerated either by orthodox or CTC (crush–tear–curl) method to express juice from the cell sap. In ortho‐ dox manufacturing, leaves are rolled under pressure and part of the juice from cell sap is expressed, whereas leaves are fully smashed and granulated in CTC maceration. The polyphenols and enzymes, which are present in different compartments in leaves, are mixed. This initiates a series of enzyme‐catalyzed oxidative reactions. Polyphenols present in leaves are oxidized to produce polymerized pigment compounds like theaflavins (TF) and thearubigins (TR). (Tanaka et al., 2009). Depending of the extent of maceration, oxida‐ tion duration ranges from 45 min to 3 hr. Major tea leaf polyphenols are catechins, which include (–) epicatechin (EC), (–) epicatechin gallate (ECG), (–) epigallocatechin (EGC), and (–) epigallocatechin gallate (EGCG) (Tanaka et al., 2009). Catechins are responsible for characteristic bitter and astringent Received: 19 March 2019 | Revised: 26 September 2019 | Accepted: 16 October 2019 DOI: 10.1111/jfpp.14283 ORIGINAL ARTICLE Analysis and modeling of major polyphenols during oxidation in production of black tea Shrilekha Das | Tanmoy Samanta | A. K. Datta Agricultural and Food Engineering Department, Indian Institute of Technology Kharagpur, Kharagpur, India Correspondence Shrilekha Das, Department of Plantation Crops and Processing, Uttar Banga Krishi Viswavidyalaya, Pundibari, West Bengal 736165, India. Email: shri137@gmail.com Present address Shrilekha Das, Department of Plantation Crops and Processing, Uttar Banga Krishi Viswavidyalaya, Pundibari, India Funding information Tea Board, Ministry of Commerce, Government of India, Grant/Award Number: IRL‐21(20)/2007‐P‐I Abstract Analysis of four different catechins, four theaflavins (TF), and thearubigin (TR) in oxidizing macerated CTC (crush–tear–curl) and rolled orthodox leaves of TV25 clone was done. Tea leaves were oxidized at different air temperatures (20, 25, 30, and 35°C) and thickness of oxidizing leaf bed (2 and 5 cm). Rate of depletion of cate‐ chins was modeled using Michaelis–Menten equation. Depletion of dihydroxylated catechins (EC, ECG) was found to be more affected by change in air temperature than trihydroxylated catechins (EGC, EGCG). Amount of maximum total TF at dif ‐ ferent temperatures was in the range of 1.19%–1.3% for CTC‐macerated leaves and 0.33%–0.43% for rolled orthodox leaves. Quadratic and linear regression equations, developed to model the change in TF and TR contents, respectively, were good fit. Bed thickness does not have any significant effect on TF content in both CTC and orthodox leaves as revealed from ANOVA. Practical applications Oxidation or fermentation of macerated leaves is a crucial step in black tea process‐ ing that needs to be carefully monitored. Tea processing facilities maintain only air humidity level during fermentation. Air temperature is also an important factor af ‐ fecting the degradation of catechins and formation of different pigment compounds. Optimum amount of unoxidized catechins and oxidized compounds TF and TR af ‐ fects the quality of final product. Modeling of catechin, TF, and TR contents in oxi‐ dizing leaves will help to manipulate processing conditions such as air temperature, duration, and bed thickness to produce good quality black tea.