Metabolomics Analysis Reveals Four Novel N-Ethyl-2-pyrrolidinone-Substituted Theaflavins as Storage-Related Marker Compounds in Black Tea

Abstract

Tea market is currently oversupplied, and unsold tea often needs to be properly stored for a period of time. However, the chemical changes occurring in black tea during storage are limitedly understood. In this study, a comprehensive nontargeted and targeted metabolomics approach was used to investigate the dynamic changes in compounds in time-series (0−19 months)-stored black teas. The contents of flavanols, theaflavins (TFs), theasinensins, procyanidins, most phenolic acids, amino acids, quercetin-Oglycosides, and myricetin-O-glycosides decreased during storage, while the contents of N-ethyl-2-pyrrolidinone-substituted flavanols, flavone-C-glycosides, and most kaempferol-O-glycosides increased. More importantly, four novel compounds strongly positively correlated with storage duration (r = 0.922−0.969) were structurally assigned as N-ethyl-2-pyrrolidinone-substituted TFs and validated with synthetic reactions of TFs and theanine standards. The content of N-ethyl-2-pyrrolidinone-substituted TFs was 51.54 μg/g in black tea stored for 19 months. To the best of our knowledge, N-ethyl-2-pyrrolidinone-substituted TFs were discovered in tea for the first time.

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

“…From a review of the formation mechanism of EPSFs, it was found that the formation of these compounds was related to temperature and microbial activities, especially during the drying stage of tea processing. 5,9,[12][13][14]31,37,41 Under higher temperatures, the contents of EPSFs significantly increased. In our previous studies, we found that EPSFs are a group of compounds, which obtained the largest increase in content after high-temperature roasting processing, 14 and their contents are negatively correlated with the bitterness and astringency intensities of tea (with Pearson correlation coefficient values between −0.84 and −0.94).…”

“…In recent years, the adducts ( N -ethyl-2-pyrrolidone-substituted flavan-3-ols (EPSFs)) of tea catechins with Strecker degradation products of theanine have become a popular research compound in tea. At present, these substances are found in six types of tea, and their health effects (anti-inflammatory, anticancer, antioxidation, prevention of senile dementia and hypoglycemia), ,,,,, as well as changes in the content of tea during processing and storage times (white tea, green tea, dark tea, and black tea), were widely studied. ,− Catechin has a strong bitter and astringent taste, while theanine possesses a umami taste. − In addition, theanine is the amino acid with the highest level in tea. ,,,− , However, the taste properties of EPSFs were less studied. From a review of the formation mechanism of EPSFs, it was found that the formation of these compounds was related to temperature and microbial activities, especially during the drying stage of tea processing. ,,− ,,, Under higher temperatures, the contents of EPSFs significantly increased.…”

“…At present, these substances are found in six types of tea, and their health effects (anti-inflammatory, anticancer, antioxidation, prevention of senile dementia and hypoglycemia), ,,,,, as well as changes in the content of tea during processing and storage times (white tea, green tea, dark tea, and black tea), were widely studied. ,− Catechin has a strong bitter and astringent taste, while theanine possesses a umami taste. − In addition, theanine is the amino acid with the highest level in tea. ,,,− , However, the taste properties of EPSFs were less studied. From a review of the formation mechanism of EPSFs, it was found that the formation of these compounds was related to temperature and microbial activities, especially during the drying stage of tea processing. ,,− ,,, Under higher temperatures, the contents of EPSFs significantly increased. In our previous studies, we found that EPSFs are a group of compounds, which obtained the largest increase in content after high-temperature roasting processing, and their contents are negatively correlated with the bitterness and astringency intensities of tea (with Pearson correlation coefficient values between −0.84 and −0.94) .…”

Metabolomics investigation of the chemical variations in white teas with different producing areas and storage durations

“…In our previous studies, we found that the compounds changed more obviously at the early stage of storage than at the late stage of storage ( Dai et al, 2020 , Chen et al, 2021 ). In this study, the samples of Zhenghe white tea (ZHWT), Fuding white tea (FDWT), and Jinggu white tea (JGWT) were collected from different production years, including 2022, 2021, 2020, 2019, and 2007 that with storage years of 0, 1, 2, 3, and 15 years, respectively.…”

Antihyperlipidemic effect and increased antioxidant enzyme levels of aqueous extracts from Liupao tea and green tea in vivo

“…The alteration of alkaloid is influenced by endogenous enzymes involved in catalysis and microbial fermentation, contributing a dramatic content increase of some alkaloids (Wang et al., 2022). Fatty acids play an important role in the formation of tea aroma quality (Chen et al., 2021).…”