Investigation of free amino acid, total phenolics, antioxidant activity and purine alkaloids to assess the health properties of non-Camellia tea

Abstract

To find novel functional beverages from folk teas, 33 species of frequently used non-Camellia tea (plants other than Camellia) were collected and compared with Camellia tea (green tea, pu-erh tea and black tea) for the first time. Data are reported here on the quantities of 20 free amino acids (FAAs) and three purine alkaloids (measured by UHPLC), total polyphenols (measured by Folin-Ciocalteu assay), and antioxidant activity (DPPH). The total amounts of FAAs in non-Camellia tea (0.62-18.99 mg/g) are generally less than that of Camellia tea (16.55-24.99 mg/g). However, for certain FAAs, the quantities were much higher in some non-Camellia teas, such as γ-aminobutyric acid in teas from Ampelopsis grossedentata, Isodon serra and Hibiscus sabdariffa. Interestingly, theanine was detected in tea from Potentilla fruticosa (1.16±0.81 mg/g). Furthermore, the content of polyphenols in teas from A. grossedentata, Acer tataricum subsp. ginnala are significantly higher than those from Camellia tea; teas from I. serra, Pistacia chinensis and A. tataricum subsp. ginnala have remarkable antioxidant activities similar to the activities from green tea (44.23 μg/mL). Purine alkaloids (caffeine, theobromine and theophylline) were not detected in non-Camellia teas. The investigation suggest some non-Camellia teas may be great functional natural products with potential for prevention of chronic diseases and aging, by providing with abundant polyphenols, antioxidants and specific FAAs.

Keywords: AABA, α-aminobutyric acid; AMQ, 6-aminoquinoline; AQC, 6-aminoquinolyl-N-hydrosysuccinimidyl carbamate; AccQ, 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate; Amino acids; Antioxidant activity; DPPH, 1,1-diphenyl-2-picryl-hydrazyl; EA, essential amino acid; EDTA, ethylene diamine tetraacetic acid; F-C, Folin-Ciocalteu; FAAs, free amino acids; GABA, γ-aminobutyric acid; GAE, gallic acid equivalents; HCA, hierarchical cluster analysis; HEA, half-essential amino acid; NEA, non-essential amino acid; Non-Camellia tea; PCA, principal component analysis; Polyphenols; Purine alkaloids; RSD, relative standard deviation; Thea, theanine; UHPLC, ultra-high performance liquid chromatography.

Graphical abstract

Figure 1

Representative UHPLC chromatograms of amino acids. (A) Standard solution (400 μmol/L): 1, aspartic acid (Asp); 2, glutamine (Glu); 3, serine (Ser); 4, histidine (His); 5, glycine (Gly); 6, arginine (Arg); 7, threonine (Thr); 8, alanine (Ala); 9, proline (Pro); 10, γ-aminobutyric acid (GABA); 11, theanine (Thea); 12, cysteine (Cys); 13, tyrosine (Tyr); 14, valine (Val); 15, methionine (Met); 16, lysine (Lys); 17, isoleucine (Ile); 18, leucine (Leu); 19, phenylalanine (Phe); 20, tryptophan (Trp). a, Solvent; b, 6-aminoquinoline (AMQ); c, α-aminobutyric acid (AABA). (B) Blank sample (Do not add tea sample, only add derivatization reagent); 2 tea samples: (C) green tea and (D) Ampelopsis grossedentata.

Figure 2

Content of amino acids in non-Camellia tea. (A) Total (total amino acid); (B) EA (essential amino acid, including His, Thr, Val, Met, Lys, Ile, Leu, Phe, Trp); (C) HEA (half-essential amino acid, including Glu, Gly, Arg, Pro, Cys, Tys); (D) NEA (non-essential amino acid including Asp, Ser, Ala); (E) GABA; (F) Thea. I, II, III, IV: corresponding to the 4 classes in Fig. 4, V: three Camellia tea (green tea, black tea and pu-erh tea).

Figure 3

Principal component analysis of amino acids in teas. (A) Scores plot of 36 teas; (B) loading plot of 36 teas; (C) scores plot of 33 non-Camellia teas; (D) loading plot of 33 non-Camellia teas. I, II, III, IV: corresponding to the 4 classes in Fig. 4.

Figure 4

Hierarchical cluster dendritic diagram of 33 non-Camellia teas. Cluster (A) is divided into I and IV, cluster (B) is divided into II and III, respectively.

Figure 5

Total phenolic content, DPPH EC₅₀ of non-Camellia tea and their relationship. (A) Total phenolic content of non-Camellia tea; (B) antioxidative activity of non-Camellia tea (mean±SD); (C) Pearson correlation between total phenolic content and antioxidative activity of non-Camellia tea. I, II, III, IV: corresponding to the 4 classes in Fig. 4, V: 3 Camellia teas (green tea, black tea and pu-erh tea).^*EC₅₀ was too high to be detected in this study conditions.

Figure 6

Chromatograms of three purine alkaloids in standard solution and different tea samples. (A) Three purine alkaloid standard solution: 1, theobromine (0.76 μmol/L); 2, theophylline (0.78 μmol/L); 3, caffeine (1.6 μmol/L); (B) green tea; (C) Ampelopsis grossedentata; (D) Mallotus oblongifolius.