Unpruning improvement the quality of tea through increasing the levels of amino acids and reducing contents of flavonoids and caffeine

Abstract

Tea tree [Camellia sinensis var. sinensis or assamica (L.) O. Kuntze], an important crop worldwide, is usually pruned to heights of 70 to 80 cm, forming pruned tea tree (PTT) plantations. Currently, PTTs are transformed into unpruned tea tree (UPTT) plantations in Yunnan, China. This has improved the quality of tea products, but the underlying reasons have not been evaluated scientifically. Here, 12 samples of sun-dried green teas were manufactured using fresh leaves from an UPTT and the corresponding PTT. Using sensory evaluation, it was found that the change reduced the bitterness and astringency, while increasing sweetness and umami. Using high performance liquid chromatography detection showed that the contents of free amino acids (theanine, histidine, isoleucine and phenylalanine) and catechin gallate increased significantly (P < 0.05), whereas the content of alanine decreased significantly (P < 0.05). A liquid chromatography–mass spectrometry-based metabolomics analysis showed that the transformation to UPTT significantly decreased the relative levels of the majority of flavonols and tannins (P < 0.05), as well as γ-aminobutyric acid, caffeine and catechin (epigallocatechin, catechin, epigallocatechin gallate, gallocatechin gallate), while it significantly increased the relative contents of catechins (gallocatechin, epicatechin, epicatechin gallate and catechin gallate), phenolic acids and some amino acids (serine, oxidized glutathione, histidine, aspartic acid, glutamine, lysine, tryptophan, tyramine, pipecolic acid, and theanine) (P < 0.05). In summary, after transforming to UPTT, levels of amino acids, such as theanine increased significantly (P < 0.05), which enhanced the umami and sweetness of tea infusions, while the flavonoids (such as kaempferol, myricetin and glycosylated quercetin), and caffeine contents decreased significantly (P < 0.05), resulting in a reduction in the bitterness and astringency of tea infusions and an increase in tea quality.

An In Vitro Catalysis of Tea Polyphenols by Polyphenol Oxidase

“…Samples were injected into an LC-ESI-MS/MS system (UPLC, Shim-pack UFLC Shimadzu CBM30A system, MS, Applied Biosystems 4500 Q-Trap). The LC-ESI-MS/MS system analytical method was performed as described previously [ 45 ]. The chromatographic separation was performed on a Waters ACQUITY UPLC HSS T3 C18 column (2.1 × 100 mm, 1.8 μm; Waters Corporation, Milford, MA, USA) at 40 ℃, and the LC parameters were as follows: injection volume, 4μL; flow rate, 0.35 mL/min; The mobile phase was a mixture of (A) 0.04% acetic acid in water and (B) 0.04% acetic acid in acetonitrile; the gradient elution was carried out: 5–95% B for 0–10 min, 95% B for 10–11 min, 5% B for 11–11.1 min, 5% B for 11.1–14 min, and 100% B for 35–45 min.…”

Application of Multi-Perspectives in Tea Breeding and the Main Directions

“…The diurnal temperature difference at 10 °C clearly affected primary and secondary metabolites, with the lowest levels of polyphenols and catechins and higher levels of amino acid and theanine synthase expression, but the actual application on a certain scale was still constrained by the environment and climate [ 180 ]. Different pruning processes also affect the quality of tea leaves, and in Yunnan tea plantations, metabolite data from the unpruned tea (UPTT) revealed that levels of amino acids leading to sweetness increased, while levels of bitter and astringent catechins and caffeine decreased [ 181 ]. The plant-growth regulator treatment of tea guava tissues located in cell suspension system subserved the accumulation of tea polyphenols and offered support for application in practical tea garden cultivation [ 182 ].…”