Combined multi-omics approach to analyze the flavor characteristics and formation mechanism of gabaron green tea.

Gabaron green tea (GAGT) has unique flavor and health benefits through the special anaerobic treatment. However, how this composite processing affects the aroma formation of GAGT and the regulatory mechanism was rarely reported. This study used nontargeted metabolomics and molecular sensory science to overlay screen differential metabolites and key aroma contributors. The potential regulatory mechanism of anaerobic treatment on the aroma formation of GAGT was investigated by transcriptomics and correlation analyses. Five volatiles: benzeneacetaldehyde, nonanal, geraniol, linalool, and linalool oxide III, were screened as target metabolites. Through the transcriptional-level differential genes screening and analysis, some CsERF transcription factors in the ethylene signaling pathway were proposed might participate the response to the anaerobic treatment. They might regulate the expression of related genes in the metabolic pathway of the target metabolites thus affecting the GAGT flavor. The findings of this study provide novel information on the flavor and its formation of GAGT.

Flavor perception and health benefits of tea.

As one of the most consumed non-alcoholic beverages in the world, tea is acclaimed for its pleasant flavor and various health benefits. Different types of tea present a distinctive flavor and bioactivity due to the changes in the composition and proportion of respective compounds. This article aimed to provide a more comprehensive understanding of tea flavor (including aroma and taste) and the character of tea in preventing and alleviating diseases. The recent advanced modern analytical techniques for revealing flavor components in tea, including enrichment, identification, quantitation, statistics, and sensory evaluation methodologies, were summarized in the following content. Besides, the role of tea in anti-cancer, preventing cardiovascular disease and metabolic syndrome, anti-aging and neuroprotection, and regulating gut microbiota was also listed in this article. Moreover, questions and outlooks were mentioned to objectify tea products' flavor quality and health benefits on a molecular level and significantly promote our understanding of the comprehensive value of tea as a satisfactory health beverage in the future.

Contribution of theanine to the temperature-induced changes in aroma profile of Wuyi rock tea.

Theanine is a distinctive amino acid in tea that plays a vital role in tea flavor during the roasting process. Model thermal reactions of total amino acids and sugars with different roasting conditions (low-fire, middle-fire, and high-fire) showed theanine competitively inhibited the formation of indole, skatole, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, and Strecker aldehydes, while greatly stimulated the production of roasty pyrazines. In addition, highest amounts of pyrazines were obtained under high-fire degree. Quantification of these reaction products in Wuyi rock tea (WRT) was realized in different roasted Dahongpao teas by means of sensomics approach. The quantitative data revealed the biggest influence of roasting temperatures on the formation of reaction products among indole, lipid oxidation products, and pyrazines, while other reaction products were only slightly affected. The findings of this study provide a fresh perspective on the impact of theanine on aroma formation during the roasting process, which will help to explore the formation of key odorants during tea production.

Insights into the Key Odorants in Large-Leaf Yellow Tea (Camellia sinensis) by Application of the Sensomics Approach.

Large-leaf yellow tea (LYT) is a yellow tea product with a specific aroma characteristic and is enjoyed with increasing enthusiasm in China. However, its key odorants are still unknown. In this study, 46 odorants in the headspace and vacuum-distillate of the tea infusion were identified via aroma extract dilution analysis. Sixteen compounds were newly found in LYT infusion. They were present in the highest flavor dilution factors together with 2-ethyl-3,5-dimethylpyrazine. All odorants were quantitated to evaluate their own odor activity values (OAVs). High OAVs were found for 2-methylbutanal (malty, 210), (E,E)-2,4-heptandienal (fatty/flowery, 170), 2-methylpropanal (malty, 120) and 2,3-diethyl-5-methylpyrazine (earthy/roasty, 110). An aroma recombinate consisting of 17 odorants (all OAVs ≥ 1) in an odorless nonvolatile LYT matrix mimicked the overall aroma of the original infusion, verifying the successful characterization of key aroma components in a LYT beverage. The knowledge of key odorants obtained showed potential for simplifying industrial flavor optimization of the LYT product.

Formation of dimethyl sulfide from the decomposition of S-methylmethionine in tea (Camellia sinensis) during manufacturing process and infusion brewing.

Dimethyl sulfide (DMS) is a typical odorant contributing a cooked corn-like odor to tea (Camellia sinensis). In the study, noticeable increases of DMS (>350%) occurred in green, black, yellow, and white tea during brewing. Thermal model and quantitative analysis of S-methylmethionine (SMM) confirmed the thermal decomposition of SMM into DMS (44-80%) in tea infusion. The quantitative analysis on green and black tea manufacturing processes demonstrated thermal decomposition of SMM (12% and 9.0%, respectively) leads to DMS formation during the drying step. Besides, DMS was firstly suggested to be biosynthesed from yet unknown precursors due to high concentrations in fresh leaves (180 and 1700 µg/kg) and increases during rolling (190 and 2800 µg/kg) and fermentation (6400 µg/kg in black tea). The findings provided new insight of DMS formation from the decomposition of SMM in tea during manufacturing process and infusion brewing, which also help exploring its biosynthetic pathway during tea production.

Effect of brewing conditions on phytochemicals and sensory profiles of black tea infusions: A primary study on the effects of geraniol and ß-ionone on taste perception of black tea infusions.

As a worldwide popular drink, black tea has always been one of the main focuses of tea studies. However, few studies have addressed the flavor profiles and related components, and most researches were based on a single factor. This study investigated the effects of multiple brewing conditions (temperature, time, water/tea ratio, and particle size) on the phytochemicals (non-volatile and volatile compounds) and sensory profiles of black tea infusions through response surface methodology. The regression models describing the brewing of detected indexes were significant (p ≤ 0.01) and reliable (R2 ≥ 0.902). The particle size led to the greatest variation of non-volatile compounds and presented negative correlations, while the water/tea ratio affected the composition of volatile compounds the most. Meanwhile, through the addition of the selected aroma compounds (geraniol and ß-ionone), an enhancement of black tea infusion sweetness was observed, proved the existence of odor-taste interaction in black tea infusions.