Untargeted Metabolomics Combined with Bioassay Reveals the Change in Critical Bioactive Compounds during the Processing of Qingzhuan Tea.

Peng-Cheng Zheng,Xiao-Chun Wan,Pan-Pan Liu,Tie-Jun Ling,Liang Zhang,Lin Feng,Jing-Ming Ning,Chun-Yin Qin

doi:10.3390/molecules26216718

Peng-Cheng Zheng, Xiao-Chun Wan + Show 6 more

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https://doi.org/10.3390/molecules26216718

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Abstract

Qingzhuan tea (QZT) is a typical Chinese dark tea that has a long-time manufacturing process. In the present study, liquid chromatography coupled with tandem mass spectrometry was used to study the chemical changes of tea samples during QZT processing. Untargeted metabolomics analysis revealed that the pile-fermentation and turnover (post-fermentation, FT) was the crucial stage in transforming the main compounds of QZT, whose contents of flavan-3-ols and flavonoids glycosides were decreased significantly. The bioactivities, including the antioxidant capacities and inhibitory effects on α-amylase and α-glucosidase, were also reduced after the FT process. It was suggested that although the QZT sensory properties improved following pile-fermentation and aging, the bioactivities remained restrained. Correlation analysis indicated that the main galloylated catechins and flavonoid glycosides were highly related to their antioxidant capacity and inhibitory effects on α-amylase and α-glucosidase.

Highlights

Qingzhuan tea (QZT), one of the most famous dark teas in China, has attracted significant attention due to its use of special manufacturing technology and long-time pilefermentation [1,2,3]
Liquid chromatography-tandem mass spectrometry and metabolomics are widely used as a potent tool in tea research, despite differences in the secondary metabolites or the chemical constituents during processing [10]
We preliminarily studied the changes of the main compounds during pilefermentation [17] and found that the polyphenols drastically decreased at the beginning of pile-fermentation [18,19]

Summary

Introduction

Qingzhuan tea (QZT), one of the most famous dark teas in China, has attracted significant attention due to its use of special manufacturing technology and long-time pilefermentation [1,2,3]. The processing steps of QZT include fixing, rolling, preliminary drying to the water content below 13%, pile-fermentation (turnover thrice and aging 3 months), steaming, shaping, and drying [4]. Raw dark teas are piled together up to 3–5 m in a warehouse. The chemical changes of raw dark tea are thought to occur during the long-term pile-fermentation, responsible for the unique flavor and health benefits [6]. Given that the QZT raw materials consist of mature leaves and stems, the chemical composition differs from that of other typical green teas, such as Longjing tea, Maofeng tea, and some black teas [8,9]. Liquid chromatography-tandem mass spectrometry and metabolomics are widely used as a potent tool in tea research, despite differences in the secondary metabolites or the chemical constituents during processing [10]. It was recently uncovered that the first stage of pile-fermentation has the strongest effect on the formation of N-ethyl-2-pyrrolidone-substituted flavan-3-ols [11]

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