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. 2024 May 7;14(1):10424.
doi: 10.1038/s41598-024-60951-5.

Changes in amino acids, catechins and alkaloids during the storage of oolong tea and their relationship with antibacterial effect

Jilai Cui #  1   2 , Bin Wu #  3 , Jie Zhou  4
Affiliations

Changes in amino acids, catechins and alkaloids during the storage of oolong tea and their relationship with antibacterial effect

Jilai Cui et al. Sci Rep. .

Abstract

The storage process has a significant impact on tea quality. Few is known about effect of storage on quality of oolong tea. This study aimed to assess the effect of different storage times on the key chemical components of oolong tea by measuring changes in catechin, free amino acid, and alkaloid content. Variation in the main substances was determined by principal component analysis and heat map analysis. The results revealed notable effects of the storage process on the levels of theanine, epigallocatechin gallate (EGCG), and glutamine. These findings suggest that these compounds could serve as indicators for monitoring changes in oolong tea quality during storage. Additionally, the study observed an increase in the antibacterial ability of tea over time. Correlation analysis indicated that the antibacterial ability against Micrococcus tetragenus and Escherichia coli was influenced by metabolites such as aspartic acid, threonine, serine, gamma-aminobutyric acid, ornithine, alanine, arginine, and EGCG. Overall, this study presents an approach for identifying key metabolites to monitor tea quality effectively with relatively limited data.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Antibacterial ability of oolong tea with different storage time. (a) Histogram of the antibacterial ability of oolong tea against Pathogenic Escherichia coli. (b) Histogram of the antibacterial ability of oolong tea against Micrococcus tetragenus. Columns with different color means oolong tea with different storage time. Ck means oolong tea without storage, 2w means oolong tea stored for 2 weeks, 4w means oolong tea stored for 4 weeks, 8w means oolong tea for 8 weeks, 12w means oolong tea stored for 12 weeks, and 16w means oolong stored for 16 weeks. The numbers on the abscissa represent incubation time of solution mixed with bacteria and tea infusion.
Figure 2
Figure 2
Antioxidant capacity of oolong tea with different storage time determined by different methods. (a) ABTS assay, (b) FRAP assay and (c) DPPH assay.
Figure 3
Figure 3
Heatmap of free amino acids in oolong tea with different storage time. Thea theanine, Phe l-phenylalanine, Cit citrulline, Arg l-arginine, Ser l-serine, Ala l-alanine, Leu l-leucine, Val l-valine, Thr l-threonine, gABA γ-aminobutyric acid, Orn l-ornithine, Gln glutamine, Gly glycine, Pro l-proline, Glu l-glutamic acid, His l-histidine, Cys l-cysteine, Ile l-isoleucine, α-AAA alpha-aminoadipic acid, Tyr l-tyrosine, bAla β-alanine, Asp aspartic acid, α-ABA α-amino-n-butyric acid.
Figure 4
Figure 4
PCA score plot and loading plot of free amino acids in tea samples during storage. (a) PCA score plot of free amino acids in tea samples during storage. (b) Loading plot of free amino acids in tea samples during storage.
Figure 5
Figure 5
Heatmap of the content of catechins and alkaloids in tea samples during storage.
Figure 6
Figure 6
Correlation between certain metabolites and their antibacterial activity against Pathogenic Escherichia coli (P, red) and Micrococcus tetragenus (M, blue). (a) Asp, aspartic acid; (b) Thr, l-threonine; (c) Ser, l-serine; (d) Ala, l-alanine; (e) Arg, l-arginine; (f) EGCG, Epigallocatechin gallate; (g) gABA, γ-aminobutyric acid; (h) Orn, l-ornithine. The abscissa represents the content of metabolites, and the ordinate means the log-transformed optical density of solution mixed with different tea infusion and bacterial culture solution. Higher optical density indicates higher bacterial activity and lower antibacterial activity of metabolite.
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