Polyphenols, the most abundant components in tea, determine the quality and health function of tea. The analysis of polyphenols in tea is a topic of increasing interest. However, the complexity of the tea matrix, the wide variety of teas, and the difference in determination purposes puts forward higher requirements for the detection of tea polyphenols. Many efforts have been made to provide a highly sensitive and selective analytical method for the determination and characterization of tea polyphenols. In order to provide new insight for the further development of polyphenols in tea, in the present review we summarize the recent literature for the detection of tea polyphenols from the perspectives of determining total polyphenols and individual polyphenols in tea. There are a variety of methods for the analysis of total tea polyphenols, which range from the traditional titration method, to the widely used spectrophotometry based on the color reaction of Folin–Ciocalteu, and then to the current electrochemical sensor for rapid on-site detection. Additionally, the application of improved liquid chromatography (LC) and high-resolution mass spectrometry (HRMS) were emphasized for the simultaneous determination of multiple polyphenols and the identification of novel polyphenols. Finally, a brief outline of future development trends are discussed.

Xinyang Maojian (XYMJ) is one of the premium green teas and originates from Xinyang, which is the northernmost green tea production area in China. The special geographic location, environmental conditions, and manufacturing process contribute to the unique flavor and rich nutrition of XYMJ green tea. Aroma is an important quality indicator in XYMJ green tea. In order to illustrate the aroma of XYMJ green tea, the key odorants in XYMJ green tea and their dynamic changes during the manufacturing processes were analyzed by headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS). A total of 73 volatile compounds of six different chemical classes were identified in the processed XYMJ green tea samples, and the manufacturing processes resulted in the losses of total volatile compounds. Among the identified volatile compounds, twenty-four aroma-active compounds, such as trans-nerolidol, geranylacetone, nonanal, (+)-δ-cadinene, linalool, (Z)-jasmone, cis-3-hexenyl butyrate, cis-3-hexenyl hexanoate, methyl jasmonate, and β-ocimene, were identified as the key odorants of XYMJ green tea based on odor activity value (OAV). The key odorants are mainly volatile terpenes (VTs) and fatty acid-derived volatiles (FADVs). Except for (+)-δ-cadinene, copaene, cis-β-farnesene, (Z,E)-α-farnesene and phytol acetate, the key odorants significantly decreased after fixing. The principal coordinate analysis (PCoA) and the hierarchical cluster analysis (HCA) analyses suggested that fixing was the most important manufacturing process for the aroma formation of XYMJ green tea. These findings of this study provide meaningful information for the manufacturing and quality control of XYMJ green tea.

Xinyang Maojian (XYMJ) green tea is one of the top ten teas in China, and the consumers prefer spring tea due to its umami taste and pleasurable aroma. However, the knowledge about temporal variation of the volatile compounds in XYMJ green teas harvested during different seasons is very limited. In the present work, the main non-volatile compounds that endowed the taste and volatile compounds responsible for the aroma in XYMJ green teas harvested during the spring and autumn seasons were determined. The average contents of free amino acids (FAA) were significantly higher and gradually declined in the spring teas, whereas the caffeine was significantly lower and gradually increased in the spring teas. A total of 39 volatile compounds of six chemical classes were detected in XYMJ green teas, and they displayed various change trends during the spring and autumn seasons, among which 15 volatile compounds were identified as the key odorants based on odor activity value (OAV). The highest OAV of 2195.05 was calculated for the violet-like smelling trans-β-ionone followed by decanal, nonanal, dimethyl sulfide, linalool, geraniol and naphthalene. The OAVs of geraniol, (Z)-3-hexenyl hexanoate, heptanal, benzaldehyde and hexanal in XYMJ spring teas were higher than XYMJ autumn teas. The hierarchical clustering analysis indicated that XYMJ green teas were divided into three clusters and the quality of XYMJ green teas changed greatly within spring season. Harvest season is a crucial factor affecting the flavor quality of XYMJ green teas.