title: Differential behaviors of tea catechins under thermal processing: Formation of non-enzymatic oligomers.
abstract: Tea catechins as a member of flavan-3-ols subclass with the same skeleton may behave differentially. This study investigated the chemical conversions of 8 catechins under heat treatment with the involvement of epimerization, hydrolysis and oxidation/condensation reactions. Three reactions were enhanced as temperature increased from 30 °C to 90 °C. The epimerization of non-gallated catechins was favored by epi-configuration but hindered by pyrogallol moiety, and the hydrolysis reaction of gallated catechins was facilitated by pyrogallol moiety. Epicatechin and epigallocatechin had the lowest thermostabilities due to epimerization and oxidation/condensation reactions respectively. Sufficient O2 was not a precondition for the occurrence of chemical conversions of catechins under heat treatment. Non-enzymatic oligomerization occurred to epi type catechins and catechin under heat treatment, and dehydrodicatechins A were mainly responsible for the browning of epicatechin and catechin solutions. The evidence of generation of catechin oligomers provides a novel way to explain sensory change of tea and relevant products during thermal processing.
authors.affiliation: Zhejiang University Tea Research Institute, Hangzhou 310058, China.
authors.forename: Fang-Yuan
authors.initials: FY
authors.lastname: Fan
authors.affiliation: Zhejiang University Tea Research Institute, Hangzhou 310058, China.
authors.forename: Meng
authors.initials: M
authors.lastname: Shi
authors.affiliation: Zhejiang University Tea Research Institute, Hangzhou 310058, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Nie
authors.affiliation: Zhejiang University Tea Research Institute, Hangzhou 310058, China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Zhejiang University Tea Research Institute, Hangzhou 310058, China. Electronic address: jx0515@163.com.
authors.forename: Jian-Hui
authors.initials: JH
authors.lastname: Ye
authors.affiliation: Zhejiang University Tea Research Institute, Hangzhou 310058, China.
authors.forename: Yue-Rong
authors.initials: YR
authors.lastname: Liang
mesh_terms: D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry*; D004355:Drug Stability; D006358:Hot Temperature; D006868:Hydrolysis; D010084:Oxidation-Reduction; D011748:Pyrogallol / Q000737:chemistry; D013662:Tea / Q000737:chemistry*
chemical_list: D013662:Tea; D011748:Pyrogallol; D002392:Catechin; C057580:gallocatechol
keywords: Catechins; Dimer; Low O(2); Steric configuration; Thermostability