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

Ruoyu Li; Kunyi Liu; Zhengwei Liang; Hui Luo; Teng Wang; Jiangshan An; Qi Wang; Xuedan Li; Yanhui Guan; Yanqin Xiao; Caiyou Lv; Ming Zhao

doi:10.3389/fnut.2022.1017693

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

Front Nutr. 2022 Sep 29:9:1017693. doi: 10.3389/fnut.2022.1017693. eCollection 2022.

Authors

Ruoyu Li^{1

2}, Kunyi Liu^{1

2

3}, Zhengwei Liang^{1

2}, Hui Luo^{1

2}, Teng Wang^{1

2}, Jiangshan An^{1

2}, Qi Wang^{1

2}, Xuedan Li¹, Yanhui Guan^{1

2}, Yanqin Xiao^{1

2}, Caiyou Lv¹, Ming Zhao^{1

2}

Affiliations

¹ College of Tea Science and College of Food Science and Technology and College of Agronomy and Biotechnology, Yunnan Agricultural University, Kunming, China.
² The Key Laboratory of Medicinal Plant Biology of Yunnan Province and National and Local Joint Engineering Research Center on Germplasm Innovation and Utilization of Chinese Medicinal Materials in Southwestern China, Yunnan Agricultural University, Kunming, China.
³ College of Wuliangye Technology and Food Engineering, Yibin Vocational and Technical College, Yibin, China.

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.

Keywords: Camellia sinensis; metabolomics analysis; pruning; sensory characteristic; sun-dried green tea.