Lipid metabolic characteristics and marker compounds of ripened Pu-erh tea during pile fermentation revealed by LC-MS-based lipidomics.

Ripened Pu-erh tea (RPT) is a unique microbial fermented tea. Herein, we investigated the lipid composition of RPT and its metabolic changes during pile fermentation, by nontargeted lipidomics profiling and quantitative analysis using liquid chromatography-mass spectrometry (LC-MS). A total of 485 individual lipid species covering 26 subclasses were detected, and fatty acid ester of hydroxy fatty acid (FAHFA) was detected in tea for the first time. Among them, 362 species were significantly altered during fermentation. Chlorophylls decomposition, phospholipids degradation (especially phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine), formation of free fatty acid (FFA) (especially FFA18:3, FFA18:2), and formation of FAHFA, were annotated as the key pathways. Particularly, FAHFAs were undetected in raw tea and gradually enriched to 227.0 ± 9.6 nmol/g after fermentation (p < 0.001), which could serve as marker compounds of RPT associated with microbial fermentation. This study will advance understanding the lipid metabolic fate in microbial fermentation and its role in RPT quality. Chemical compounds studied in this article: Linolenic acid (PubChem CID: 5280934); Linoleic acid (PubChem CID: 5280450); Oleic acid (PubChem CID: 445639); PS(22:0/18:2) (PubChem CID: 52925820); PS(20:0/18:3) (PubChem CID: 52925629); Pheophytin a (PubChem CID: 135398712); Pheophorbide a (PubChem CID: 253193).

Insight into aroma dynamic changes during the whole manufacturing process of chestnut-like aroma green tea by combining GC-E-Nose, GC-IMS, and GC × GC-TOFMS.

Processing is the crucial factor for green tea aroma quality. In this study, the aroma dynamic changes throughout the manufacturing process of chestnut-like aroma green tea were investigated with gas chromatography electronic nose (GC-E-Nose), gas chromatography-ion mobility spectrometry (GC-IMS), and comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-TOFMS). GC-IMS identified 33 volatile compounds while GC × GC-TOFMS identified 211 volatile components. Drying exerted the greatest influence on the volatile components of chestnut-like aroma green tea, and promoted the generation of heterocyclic compounds and sulfur compounds which were commonly generated via the Maillard reaction during the roasting stage. A large number of heterocyclic compounds such as 1-methyl-1H-pyrrole, pyrrole, methylpyrazine, furfural, 2-ethyl-5-methylpyrazine, 1-ethyl-1H-pyrrole-2-carboxaldehyde, and 3-acetylpyrrole were newly formed during the drying process. This study also validated the suitability of GC-E-Nose combined with GC-IMS and GC × GC-TOFMS for tracking the changes in volatile components of green tea throughout the manufacturing process.

Volatile Analysis of Wuliangye Baijiu by LiChrolut EN SPE Fractionation Coupled with Comprehensive GC×GC-TOFMS.

Wuliangye baijiu is one of the most famous Chinese liquors with a protected geographical indication. This study used LiChrolut® EN-based solid-phase extraction (SPE) and fractionation combined with comprehensive two-dimensional chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) to unveil its volatile composition. The volatiles were isolated with LiChrolut® EN-based SPE and traditional liquid-liquid extraction (LLE). The neutral/basic fractions from LLE and the SPE were fractionated on a LiChrolut® EN SPE column and analyzed by comprehensive GC×GC-TOFMS. Compared with LLE, more esters and alcohols were detected in the SPE-based extraction. The SPE fractionation and GC×GC-TOFMS analysis resulted in the identification of about 500 volatile compounds in more than 3000 peaks of the Wuliangye baijiu. The approach simplifies the complex baijiu composition into functional group-based fractions for reliable identification and analysis. This study provided a confidence volatile identification approach for Chinese baijiu based on the SPE fractionation GC×GC-TOFMS.

Aroma dynamic characteristics during the process of variable-temperature final firing of Congou black tea by electronic nose and comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry.

The drying technology is crucial to the quality of Congou black tea. In this study, the aroma dynamic characteristics during the variable-temperature final firing of Congou black tea was investigated by electronic nose (e-nose) and comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-TOFMS). Varying drying temperatures and time obtained distinctly different types of aroma characteristics such as faint scent, floral aroma, and sweet fragrance. GC × GC-TOFMS identified a total of 243 volatile compounds. Clear discrimination among different variable-temperature final firing samples was achieved by using partial least squares discriminant analysis (R2Y = 0.95, Q2 = 0.727). Based on a dual criterion of variable importance in the projection value (VIP > 1.0) and one-way ANOVA (p < 0.05), ninety-one specific volatile biomarkers were identified, including 2,6-dimethyl-2,6-octadiene and 2,5-diethylpyrazine with VIP > 1.5. In addition, for the overall odor perception, e-nose was able to distinguish the subtle difference during the variable-temperature final firing process.

Introduction to the Second International Flavor and Fragrance Conference.

The Second International Flavor and Fragrance Conference was successfully held on May 28-31, 2018, in Wuxi, China. The congress shared the progresses and discoveries in the research areas of flavor and fragrance perception, flavor analysis, thermal and biomediated generation of flavor, biological activities of aroma and flavor, and flavor and fragrance encapsulation and delivery technologies. This special issue collected some original research papers as well as reviews on basic taste, flavor analysis, aroma and taste characterization, essential oil bioactivity, and other related topics.

Flavor and chiral stability of lemon-flavored hard tea during storage.

Flavor stability of hard tea beverage was investigated over eight weeks of storage. The volatile compounds were analyzed using solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and two-dimensional GC-MS. Quantitative analysis showed that the concentrations of linalool, citronellol, geranial, neral, geraniol, and nerol decreased dramatically during storage, whereas α-terpineol showed an increasing trend during storage. Heart-cut two-dimensional GC-MS (2D-GC-MS) chirality analysis showed that (R)-(+)-limonene, (R)-(-)-linalool, (S)-(-)-α-terpineol and (S)-(-)-4-terpineol dominated in the fresh hard tea samples, however, the configuration changed during storage for the terpene alcohols. The storage conditions did not change the configuration of limonene. A conversion of (R)-(-)-linalool to (S)-(+) form was observed during storage. Both (S)-α-terpineol and (S)-4-terpineol dominated at beginning of the storage, but (R)-(+)-α-terpineol became dominated after storage, suggested in addition to isomerization from (S)-α-terpineol, other precursors could also generate α-terpineol with (R)-isomer preference.

Aroma Stability of Lemon-Flavored Hard Iced Tea Assessed by Chirality and Aroma Extract Dilution Analysis.

The aroma of fresh and aged lemon-flavored hard tea was investigated by aroma extract dilution analysis (AEDA), quantitative comparison, and two-dimensional chirality analysis. Aroma extract dilution analysis of fresh hard tea samples showed 3-methylbutanal, isoamyl alcohol, ß-damascenone, ß-ionone, 2-phenylethanol, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, and vanillin could be the most important aroma contributors to the hard tea due to their high FD values. The analysis of the aged hard tea samples did not reveal new compound formation during storage; however, compared with fresh samples, the flavor dilution value changed substantially in the aged samples. Both AEDA and quantitative analysis demonstrated that ß-damascenone increased substantially in aged samples, whereas terpene aldehydes decreased substantially after storage. In addition, the FD value of linalool decreased dramatically in aged samples. Two-dimensional GC-MS chirality analysis revealed the FD value decrease of linalool in aged samples was largely due to the transformation of (R)-linalool to (S)-linalool, which has a higher sensory threshold.

Volatile compounds and sensory attributes of wine from Cv. Merlot (Vitis vinifera L.) grown under differential levels of water deficit with or without a kaolin-based, foliar reflectant particle film.

The volatile composition and sensory attributes of Merlot wines produced from vines under differing levels of water stress, with or without a foliar, kaolin-based particle film, were analyzed by stir bar sorptive extraction-gas chromatography-mass spectrometry (SBSE-GC-MS) and sensory evaluation. Vines were irrigated over consecutive vintages with 100, 70, or 35% of their estimated water requirements (ET(c)), or 35% until color change then 70% until harvest (35-70% ET(c)). Neither of the treatments consistently influenced ester concentrations or their relative amounts, though their concentrations varied from year to year. However, deficit irrigation had an effect on the concentration of terpene alcohols and norisoprenoids. Wines produced from vines under water deficit contained higher amounts of citronellol, nerol, geraniol, and ß-damascenone, but linalool and ß-ionone were not affected by deficit irrigation. Particle film did not affect volatile composition in the wine. Untrained panelists in 2007 and 2008 distinguished between wines from vines that received 100 or 35% ET(c) and between wines from vines that received 35 or 35-70% ET(c). Trained sensory panelists detected differences among wines for aroma, flavor, taste, and mouthfeel; however, significant interactive effects between particle film application and vine water status hindered interpretation of independent main effects.