Fresh leaves of Fuding Dabai tea (Camellia sinensis (L.)) consisting of one bud and two leaves were used to manufacture Congou black tea, and the changes in the physicochemical properties and microstructure of the bud and the two leaves were explored during the manufacturing process. It was found that during the rolling process, the color of the bud and the leaves gradually turn from green to red, but the degree of color change of the lower leaf was lower than that of the bud and the upper leaf. Besides, optical microscopic (OM) and transmission electron microscopic (TEM) analysis showed the structures of mesophyll cells and chloroplasts in both leaves were destroyed in the rolling process, indicating the beginning of fermentation. The chemical composition analysis showed that during the Congou black tea manufacturing process, the contents of tea polyphenols and catechins decreased, the contents of theaflavins and thearubigins increased at first, then decreased and finally leveled off, and the content of theabrownins kept increasing; the contents of all these compounds changed most during rolling. There was no significant difference in the oxidation degree of total catechins, epigallocatechin, epigallocatechin gallate, epicatechin gallate and theaflavins between the two leaves (P > 0.05), indicating that their fermentation degrees were similar. During the entire process, the contents of chlorophyll a, chlorophyll b and total chlorophyll decreased and the contents of pheophytin and pheophorbide increased for the bud and the leaves. The content of chlorophylls in the lower leaf was always much higher than that in the upper leaf (P < 0.05). This study provides a theoretical basis for processing high-quality congou black tea by improving the utilization rate of fresh tea leaves.

As one of the most popular beverages in the world, tea is highly susceptible to mold contamination during its planting, processing, and distribution. Toxigenic fungi produce mycotoxins under suitable conditions, and humans drinking tea may be at risk of ingesting mycotoxins. In this review, we briefly describe the sources, types, and hazards of mycotoxins in tea, summarize the current status of mycotoxin contamination in tea, discuss the advantages and disadvantages of mycotoxin detection technologies, and outline the prevention and control measures for mycotoxins in tea. This article is expected to provide a reference for the quality control of tea.

In order to investigate the changes in the characteristic aroma components of sun-dried green tea during processing, the volatile substances in fresh, fixated, rolled and sun-dried leaves of Yunnan large leaf tea were determined using solvent flavor-assisted evaporation extraction (SAFE) combined with gas chromatography-mass spectrometry (GC-MS), and the aroma active components of sun-dried green tea were identified by odor activity value (OAV). The results showed that totally 67 volatile compounds were detected, the major ones being alcohols, esters and aldehydes, and the total amount of volatile substances increased from fresh leaves to the end of fixation. The total amount of volatile substances slightly decreased in sun-dried leaves compared to fresh leaves, but the number of volatile substances increased. A total of 23 aroma active compounds with OAV > 1 were found in sun-dried green tea, with the major ones being those contributing to floral and green aromas such as linalool, geraniol and nonanal. Aldehydes were the most prominent component in each processing stage. Using gas chromatography-flame ionization detector (GC-FID) and high performance liquid chromatography-photo-diode array (HPLC-PDA), a total of 7 fatty acids were detected, with saturated fatty acids being the major components; 13 carotenoids were detected, including lutein, whose content was the highest in all processing stages. During the processing of sun-dried green tea, the total amounts of fatty acids and carotenoids decreased continuously, especially linoleic acid and linolenic acid, and the content of hexanal as their major degradation product showed the opposite trend. The contents of terpene ketones, ionone and its oxidized derivatives such as β-ionone and 5,6-epoxy-β-ionone significantly increased as a result of the degradation and transformation of carotenoids. The trends of fatty acids and carotenoid precursors during the processing of sun-dried green tea were correlated with their associated aroma products. In conclusion, the results of this study may provide theoretical guidance for the targeted aroma improvement of sun-dried green tea.

According to the results of sensory evaluation performed by experts, 14 black tea samples were divided into two groups based on their aroma quality: high-quality and quality-deficient black tea. Using fast gas chromatography-electronicnose (GC-E-Nose) and gas chromatography-mass spectrometry (GC-MS) combined with multivariate statistical analysis, discriminant analysis of the two groups were carried out, and the key differential components between these groups were selected. The results showed that 117-dimensional dataset was obtained by the fusion of the GC-E-Nose (44-dimensional) and GC-MS (73-dimensional) data and used to establish a model for accurate classification of the two types of black tea employing orthogonal partial least squares-discriminant analysis (OPLS-DA). The model’s explanatory and predictive capacity (R_Y² =0.976, Q²=0.959) were better than those of the model established based on the GC-E-Nose or GC-MS data. Based on variable important in projection (VIP) scores > 1.6 and P < 0.05, eight key aroma components including dimethyl sulfide (B3 and B25), β-ionone (A59), (3E)-4,8-dimethylnon-1,3,7-triene (A20), dihydroactinidiolide (A64), linalool (A17), phenylethyl alcohol (A19), δ-octyl lactone (A41) and γ-nonalatone (A45) were selected, which played an important role in the classification. These results showed that GC-E-Nose combined with GC-MS allows rapid and accurate discrimination between quality-deficient and high-quality black tea, which can be used as a supplement to traditional sensory evaluation, providing technical support for quality control and improvement of black tea.

In this study, sensory evaluation, headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and odor activity value (OAV) were used to evaluate the aroma quality of pearl orchid flowers in five developmental stages: bud, initial bloom, semi-bloom, full bloom, and withering. Subsequently, principal component analysis (PCA), orthogonal partial least squares-discriminant analysis (OPLS-DA) and permutation tests were performed. The results showed that there were differences in the sensory evaluation and the types and contents of volatile compounds among pearl orchid flowers at different developmental stages. The fully blooming flower had the best aroma quality, being pure and long-lasting, followed by the semi-blooming and initially blooming flowers, which had a faint flowery aroma. The withering flowers had a flowery aroma with spoilage odor and the buds had no flowery aroma, but instead had a green odor, so neither of them could be used to scent tea. A total of 98 volatile compounds were detected at levels in the range of 77.521-200.838 μg/g, including 22 alcohols, 13 aldehydes, 36 olefins, 14 esters, 4 ketones and 9 others. The content of volatile compounds in the fully blooming flowers was the highest, including 28 aroma compounds with OAV > 1 and 9 substances with OAV > 50. Due to its good appearance, aroma characteristics and aroma release capacity, the fully blooming flowers were used to scent green tea and black tea. It was found that the contents of aroma components such as methyl jasmonate of pearl orchid flowers in the scented tea were obviously increased compared with those in the plain tea, indicating improved aroma quality of tea. To sum up, the fully blooming flowers of pearl orchid is the most suitable for making scented tea.

Pu-erh ripen tea becomes popular worldwide owing to its unique taste and aroma. In the present study, volatile compounds from Pu-erh ripen tea were extracted using a solvent assisted flavor evaporation (SAFE) and analyzed with a gas chromatography-mass spectrometry (GC-MS) and a gas chromatography olfactometry (GC-O). Results demonstrated that 58 major volatile compounds and 24 aroma active substances of Pu-erh ripen tea were identified by GC-MS and GC-O analysis. Among volatile compounds identified, methoxyphenyl compounds were considered as the dominate compounds in the aroma of Pu-erh ripen tea. Further investigation showed that 6 methoxybenzenes were responsible for the aging aroma in Pu-erh ripen tea; α-ionone, 3,4-dimethoxytoluene, 1,3-dimethoxybenzene, etc. were responsible for the wood-like aroma. Linalool, α-terpineol, α-ionone, β-ionone, and benzeneacetaldehyde were responsible for the floral odor. Compared the odor detection threshold (ODT) among the 8 methoxyphenyl compounds in water, 1,2,3-trimethoxybenzene showed the highest ODT, followed by 3,4-dimethoxyphenol. 1,3-Dimethoxybenzene (105 μg/L) and 1,2,3-trimethoxy-5-methylbenzene (100 μg/L) were present at relatively low odor threshold values. The result indicated that methoxyphenyl compounds play a vital role in the unique flavor of Pu-erh ripen tea.