Formation Mechanism of Di-N-ethyl-2-pyrrolidinone-Substituted Epigallocatechin Gallate during High-Temperature Roasting of Tea

Abstract

Four di-N-ethyl-2-pyrrolidinone-substituted epigallocatechin gallate (EGCG) and two di-N-ethyl-2-pyrrolidinonesubstituted gallocatechin gallate (GCG) flavan-3-ols (di-EPSFs) were prepared by the thermal simulation reaction. The effects of reaction temperature and time, initial reactant ratios, and pH values on the content of di-EPSFs were studied. The formation of six di-EPSFs was most favored when the initial reactant ratio of EGCG and theanine was 1:2 and heated under 130 °C at pH 10 for 120 min. The contents of di-EPSF1, di-EPSF2, and di-EPSF5 in large-leaf yellow tea (LYT) increased with the increase of roasting degree. Through quantitative analysis, it was found that EGCG would interact with the Strecker degradation products of theanine to form EPSFs, which further combined with the Strecker degradation products of theanine to form di-EPSFs. This study further improved the understanding of the transformation pathways of EGCG and theanine during tea processing and contributed to exploring the flavor characteristics and health benefits of di-EPSFs.

New Insights into the Umami and Sweet Taste of Oolong Tea: Formation of Enhancer N-(1-carboxyethyl)-6-(hydroxymethyl) pyridinium-3-ol (Alapyridaine) in Roasting Via Maillard Reaction

“…It is known that catechins undergo epimerization and degradation during thermal processing, and previous studies reported high-temperature roasting of green tea, oolong tea, and yellow tea promoted the epi -structured catechins (EGCG, EGC, ECG, EC) transform to be non- epi structured catechins (GCG GC, CG, C), and total catechin content decreased in roasted tea. , Some flavonoid glycosides, such as kaempferol-3-O-β- d -galactoside, kaempferol-7-galactoside-3-rutinoside, myricetin-3-O-β- d -glucoside, myricetin-3-galactoside, and quercetin-3-O-β- d -glucoside, impart an astringent taste with very low threshold. Their contents were decreased more than 25%, tentatively consistent with the previous result. , Conversely, the concentration of N -ethyl-2-pyrrolidinone-substituted flavab-3-ols (EPSFs) increased. , A previous study suggested that EPSFs were found to rapidly rise withing roasting temperature and could be as the maker compounds during roasting . EPSFs have been shown to possess higher bitterness and astringency thresholds than EGCG, which partially explains the reduced bitter and astringent taste (Figure B,C).…”

“…2,37 Conversely, the concentration of N-ethyl-2-pyrrolidinone-substituted flavab-3-ols (EPSFs) increased. 38,39 A previous study suggested that EPSFs were found to rapidly rise withing roasting temperature and could be as the maker compounds during roasting. 33 EPSFs have been shown to possess higher bitterness and astringency thresholds than EGCG, which partially explains the reduced bitter and astringent taste (Figure 1B,C).…”

Novel Flavonol Alkaloids in Green Tea: Synthesis, Detection, and Anti-Alzheimer’s Disease Effect in a Transgenic Caenorhabditis elegans CL4176 Model

“…25,39 Jiang et al found that EPSFs could further combine with the Strecker degradation products of theanine to form di-N-ethyl-2pyrrolidiones-substituted epigallocatechin gallate (di-EPSFs) by heating under 130 °C, pH 10 for 120 min. 40 In this study, under acidic conditions, myricetin reacted with L-theanine to produce not only A-ring-substituted flavonol alkaloids like 2 and 3 but also a B-ring-substituted flavonol alkaloid like 1. However, in the reaction with quercetin and kaempferol as substrates, no B-ring substitution products were detected.…”

“…Theanine is supposed to degrade and transform into the corresponding Strecker aldehyde, which then spontaneously cyclizes to form 1-ethy-5-carboxyl-pyrrrolidone and then reacts with catechins to form N -ethyl-2-pyrrolidinone-ubstituted flavan-3-ols (EPSFs), namely, flavoalkaloids. , Jiang et al found that EPSFs could further combine with the Strecker degradation products of theanine to form di- N -ethyl-2-pyrrolidiones-substituted epigallocatechin gallate (di-EPSFs) by heating under 130 °C, pH 10 for 120 min . In this study, under acidic conditions, myricetin reacted with l -theanine to produce not only A-ring-substituted flavonol alkaloids like 2 and 3 but also a B-ring-substituted flavonol alkaloid like 1 .…”

Comprehensive applications of metabolomics on tea science and technology: Opportunities, hurdles, and perspectives

“…During this step, tea leaves were repeatedly roasted over smoldering charcoal at high temperature (usually 120–150°C) for a long period of time, and the composition as well as contents of metabolites varied significantly. Numerous studies has revealed that high temperature roasting induced the epimerization of (2 R ,3 R )‐epicatechins to (2 S ,3 R )‐catechins, the degradation of galloylated catechins to non‐galloylated catechins, and the interaction of catechins with amino acids ( e.g ., theanine) or monosaccharides ( e.g ., glucose), which caused the large fluctuation of these metabolites and the formation of some adducts such as N ‐ethyl‐2‐pyrrolidinone substituted flavan‐3‐ols (EPSFs) and 6/8 C glucose substituted EGCG (Cao et al., 2021; Gao et al., 2022; Guo, Ho, Schwab et al., 2021; Jiang et al., 2023; Jiang, Han et al., 2021; Peng, Dai et al., 2022; Zhou, Wu et al., 2019). Furthermore, roasting temperature dominated the direction of catechins response, for example, higher level of GCG was found in tea leaves roasted under higher temperature (145–150°C) while higher levels of EGC, gallocatechin, and GA were found in tea leaves roasted under relative lower temperature (120–130°C) (Guo, Ho, Schwab et al., 2021; Jiang, Han et al., 2021).…”