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

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.

Keywords: bioactivities; metabolomics; pile-fermentation; qingzhuan tea; sensory evaluation.

Figure 1

Sensory evaluation on the color and taste (mainly astringency) of QZT samples from the different processing stages. The first line above the abbreviations of tea samples showed the color of tea leaves, and the second line showed the color of tea infusions. The numbers under the abbreviations of tea samples represent their corresponding astringent scores.

Figure 2

Multivariate analysis based on the LC-Q-TOF-MS data of QZT samples from different processing stages.

Figure 3

Metabolomics analysis of QZT samples from different processing stages. (A) Scatterplots based on OPLS-DA analysis between the two categories of QZT samples. (B) S-plots based on OPLS-DA analysis between the two categories of QZT samples.

Figure 4

The inhibitory effects of different QZT samples on α-amylase and α-glucosidase. (A) Inhibitory rates of different QZT samples with various concentrations on α-amylase. (B) IC₅₀ values of different QZT samples on α-amylase: FTL: 63.48 mg/mL; DTL: 54.59 mg/mL; RTL: 29.47 mg/mL; CT: 32.59 mg/mL; 1st FT: 61.93 mg/mL; 2nd FT: 70.16 mg/mL; 3rd FT: 55.42 mg/mL; 1MAT: 73.86 mg/mL; 3MAT: 63.98 mg/mL; 6MAT: 49.07 mg/mL; DT: 68.88 mg/mL. (C) Inhibitory rates of different QZT samples with various concentrations on α-glucosidase. (D) IC₅₀ values of different QZT samples on α-glucosidase: FTL: 60.54 μg/mL; DTL: 52.91 μg/mL; RTL: 61.01 μg/mL; CT: 69.57 μg/mL; 1st FT: 66.26 μg/mL; 2nd FT: 71.60 μg/mL; 3rd FT: 145.60 μg/mL; 1MAT: 72.54 μg/mL; 3MAT: 94.72 μg/mL; 6MAT: 135.57 μg/mL; DT: 107.94 μg/mL.

Figure 5

The antioxidant activity of different samples during QZT processing. (A) ABTS scavenging rates of different QZT samples. (B) IC₅₀ values of different QZT samples on ABTS scavenging: FTL: 1.17 mg/mL; DTL: 0.96 mg/mL; RTL: 0.97 mg/mL; CT: 1.00 mg/mL; 1st FT: 1.75 mg/mL; 2nd FT: 1.81 mg/mL; 3rd FT: 1.36 mg/mL; 1MAT: 1.44 mg/mL; 3MAT: 1.75 mg/mL; 6MAT: 1.37 mg/mL; DT: 1.52 mg/mL. (C) DPPH scavenging rates of different QZT samples. (D) IC₅₀ values of different QZT samples on DPPH scavenging: FTL: 22.38 μg/mL; DTL: 21.27 μg/mL; RTL: 17.72 μg/mL; CT: 18.28 μg/mL; 1st FT: 40.43 μg/mL; 2nd FT: 26.69 μg/mL; 3rd FT: 27.99 μg/mL; 1MAT: 32.03 μg/mL; 3MAT: 35.71 μg/mL; 6MAT: 26.38 μg/mL; DT: 32.14 μg/mL. (E) The calibration curve of Fe²⁺. (F) FRAP values of different QZT samples with different concentrations (0.05–1 mg/mL).