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Decaffeinated teas (DTs) are preferred for their low caffeine content, but their flavor was unsatisfactory. To explore and optimize the flavor of DT decaffeinated by supercritical carbon dioxide (SCD), the volatiles and non-volatiles were analyzed using mass spectrometry. Results showed that SCD results in the loss of the original tea flavor by reducing the volatiles associated with floral aroma and non-volatiles related to sweet and mellow. Scenting significantly optimized the comprehensive flavor of DTs by blending DTs with fresh jasmine. The aroma of DTs was improved by absorbing the high concentration of volatiles released by jasmine, and their jasmine taste resulted from the subsequent release of methyl anthranilate dissolved in tea infusion. Jasmine decaffeinated tea with a powerful and long-lasting jasmine aroma can be obtained with 100 % amount of flowers. The scenting provided in this study can effectively optimize the flavor of DTs, thereby positively impacting the development of DTs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Ltd.)

Fu Brick Tea (FBT) is a unique fermented tea produced in multiple regions of China, whose aroma qualities, key odor-active compounds and bacterial communities are not well characterized. By optimizing HS-SPME methods, utilizing GC-MS, GC-O, sensory analysis, aroma recombination and omission experiments, and bacterial sequencing, we revealed the primary volatiles and bacterial communities in 41 samples from 7 major producing regions. A total of 63 volatiles and 32 odor-active compounds were quantitatively analyzed using GC-MS and GC-O, respectively. Sensory analyses discriminated the quality of the samples. Differential analysis indicated that poor aroma FBTs had either low volatile content or excessive "green" notes. Key odor-active compounds in high-quality aroma FBTs include 1-octen-3-ol, phenylethylalcohol, β-ionone, dihydroactindiolide, and 1,2,3-trimethoxybenzene. Sequencing results identified Bacillus, Pseudomonas, and Streptococcus as dominant genera. Functional prediction analyses suggest that bacteria contribute to the formation of FBT aroma. This study offers new insights into the quality characteristics of FBT., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Dark tea (DT) holds a rich cultural history in China and has gained sizeable consumers due to its unique flavor and potential health benefits. In this study, headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS), relative odor activity value (ROAV), and chemometrics approaches were used to detect and analyze aroma compounds differences among five dark teas from different geographical regions. The results revealed that the five DTs from different geographical regions differed in types, quantities, and relative concentrations of volatile compounds. A total of 1372 volatile compounds of were identified in the 56 DT samples by HS-SPME-GC-MS. Using ROAV and chemometrics approaches, based on ROAV>1 and VIP>1. Eighteen key aroma compounds can be used as potential indicators for DT classification, including dihydroactinidiolide, linalool, 1,2,3-trimethoxybenzene, geranyl acetone, 1,2,4-trimethoxybenzene, cedrol, 3,7-dimethyl-1,5,7-octatrien-3-ol, β-ionone, 4-ethyl-1,2-dimethoxybenzene, methyl salicylate, α-ionone, geraniol, linalool oxide I, linalool oxide II, 6-methyl-5-hepten-2-one, α-terpineol, 1,2,3-trimethoxy-5-methylbenzene, and 1,2-dimethoxybenzene. These compounds provide a certain theoretical basis for distinguishing the differences in five DTs from different geographical regions. This study provides a potential method for identifying the volatile substances in DTs and elucidating the differences in key aroma compounds. Abbreviations: DT, dark tea; FZT, Fuzhuan tea; LPT, Guangxi Liupao tea; QZT, Hubei Qingzhuan tea; TBT, Sichuan Tibetan tea; PET, Yunnan Pu-erh tea; ROAV, Relative odor activity value; OT, Odor threshold; HS-SPME, Headspace solid-phase microextraction; GC-MS, Gas chromatography-mass spectrometry; PCA, Principal components analysis; PLS-DA, Partial least squares-discriminant analysis; HCA, Hierarchical clustering analysis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

This study investigates the dynamic changes in the aroma profile of Tuo tea during long-term storage, a process not well understood yet critical to the formation of aged tea's unique characteristics. Aroma profiling of Tuo tea samples stored for 2 to 25 years was conducted using sensory evaluation and the HS-SPME/GC × GC-QTOFMS technique, revealing a progressive transition from fresh, fruity, and floral scents to more stale, woody, and herbal notes. Among 275 identified volatiles, 55 were correlated with storage duration (|r| > 0.8, p < 0.05), and 49 differential compounds (VIP > 1, FC > 1.2, FC < 0.833, p < 0.05) were identified across three storage stages (2-4, 5-10, and 13-25 years). Furthermore, theaspirane, eucalyptol, o-xylene, and 1-ethylidene-1H-indene were selected as potential markers of Tuo tea aging, incorporating the implementation of a Random Forest (RF) model. Additionally, our model exhibited high accuracy in predicting the age of Tuo tea within a prediction error range of -2.51 to 2.84 years. This research contributes to a comprehensive understanding of the impact of storage time on tea aroma and aids in the precise identification of tea age., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Aroma is one of the significant quality factors of dark tea (DT). However, for a single large-leaf tea variety, there are few studies analyzing the effect of pile-fermentation on the aroma quality of DT. The GC × GC-QTOFMS, electronic nose (E-nose) and GC-olfactometry (GC-O) techniques were employed to analysis the difference of tea products before and after pile-fermentation. A total of 149 volatile metabolites (VMs) were identified, with 92 VMs exhibiting differential characteristics. Among these, 31 VMs with OAV > 1.0 were found to be correlated with E-nose results (|r| > 0.8). Additionally, GC-O analysis validated seven major differential metabolites. Notably, naphthalene, 2-methylnaphthalene, and dibenzofuran were found to enhance the woody aroma, while (Z)-4-heptenal, 2-nonenal and 1-hexanol were associated with an increase in mushroom, fatty and sweet odors, respectively. Moreover, 1-octen-3-ol was linked to reducing pungent fishy smell. These findings could provide a certain theoretical basis for understanding the influence of pile-fermentation on the aroma quality of dark tea., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Fu brick tea (FBT) is popular for its unique 'fungal flower' aroma, however, its key odor-active compounds are essentially unknown. In this study, the odor-active compounds of "stale-fungal" aroma (CJX), "fresh-fungal" aroma (QJX), and "fermentation-fungal" aroma (FJX) types FBT were extracted and examined by headspace solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and gas chromatographyolfactometry (GC-O). A total of 43 volatile and 38 odor-active compounds were identified by these methods. Among them, the content of dihydroactindiolide (4596-13189 µg/L), (E)-linalool oxide (2863-6627 µg/L), and benzyl alcohol (4992-6859 µg/L) were highest. Aroma recombination experiments further verified that these odor-active compounds could be simulated the overall aroma profile of FBT successfully. Furthermore, omission experiments confirmed that 15, 20, and 15 key odor-active compounds in CJX, QJX, and FJX FBT, respectively. This study will provide a theoretical basis for comprehensively understanding the formation of characteristic aromas in FBT., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The aroma quality of jasmine tea refers to the strength and freshness of jasmine fragrance and its coordination with tea aroma, which is regulated by various volatile compounds. In this study, seventy volatile compounds of jasmine tea scented by different scenting technology were analyzed qualitatively and quantitatively by gas chromatography-mass spectrometry (GC-MS). And seven compounds were identified as the key volatile compounds by weighted gene co-expression network analysis (WGCNA), orthogonal partial least squares discriminant analysis (OPLS-DA) and odor activity value (OAV). According to the equation describing seven key volatile compounds and quality of jasmine tea, the optimal scenting technology was obtained, that is, the amount of flowers (AF) was 65-78%, scenting time (ST) was 15-17 h, and scenting temperature (SW) was 35-40 °C. This study lays a foundation for the study of aroma characteristics of jasmine tea, and guides enterprises to improve jasmine tea processing technology., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Changes in key odorants and aroma profiles of Qingzhuan tea (QZT) during its manufacture were determined using headspace solid-phase microextraction gas chromatography-mass spectrometry/olfactometry. An aroma profile was constructed to illustrate sensory changes during manufacture. The characteristic aroma of QZT was aged fragrance, which was mostly developed during pile fermentation and was enhanced during the aging and drying stages. Using volatile compounds found in the raw materials, sun-dried green tea and QZT finished product were compared by orthogonal partial least square-discriminant analysis. Among 108 detected volatiles, 19 were significantly upregulated and 15 were downregulated. (E)-β-Ionone, (E,Z)-2,6-nonadienal, 1-octen-3-one, (E,E)-2,4-heptadienal, (E,E)-2,4-nonadienal, safranal, (E)-2-nonenal, α-ionone, and 1,2,3-trimethoxybenzene were found to be significant contributors to the aged QZT fragrance, reflecting their high odor-activity values and aroma intensities. Finally, the metabolic transformation of key aroma-active compounds was systematically analyzed. This study provided a theoretical basis for improving the processing and quality of QZT., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Liupao tea is a representative Chinese dark tea. Stale-aroma type, betelnut-aroma type and fungal-aroma type were the main aroma types of Liupao tea. In this study, aroma profiles and fungal communities of the three aroma types of Liupao tea were examined by HS-SPME/GC-MS and Illumina MiSeq analysis. A total of 102 volatiles were identified and quantified in Liupao tea. Indicated by OPLS-DA analysis, six aroma compounds with stale, woody, roasted notes in stale-aroma type samples, five aroma compounds possessing smoky, minty, pungent notes in betelnut-aroma type samples, and nine aroma compounds owned minty, floral, fruity, woody, green notes in fungal-aroma type samples were responsible for the different aroma characteristics formation of Liupao tea. In addition, a total of 60 fungal genera were identified in Liupao tea. Aspergillus, Wallemia, Xeromyces were the predominant fungal genera in Liupao tea. Ten fungal genera, including Wallemia, Tritirachium, Debaryomyces, Trichomonascus, unclassified&#95;o&#95;Hypocreales in betelnut-aroma type, Rasamsonia, Candida, Blastobotrys, Acremonium in stale-aroma type, and Xeromyces in fungal-aroma type, were identified as the biomarkers in the three aroma types of Liupao tea. Furthermore, fungal genera including Aspergillus, Wallemia, Xeromyces, and Blastobotrys were identified as the core functional microorganisms contributing to the variation of volatile profiles based on O2PLS analysis. This study provided useful information on the key aroma compounds and core functional microorganisms that drive the different aroma characteristics formation of Liupao tea., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Jasmine tea is widely loved by the public because of its unique and pleasant aroma and taste. The new scenting process is different from the traditional scenting process, because the new scenting process has a thin pile height to reduce the high temperature and prolong the scenting time. We qualified and quantified volatiles in jasmine and jasmine tea during the scenting process by gas chromatography-mass spectrometry (GC-MS) with a headspace solid-phase microextraction (HS-SPME). There were 71 and 78 effective volatiles in jasmine and jasmine tea, respectively, including 24 terpenes, 9 alcohols, 24 esters, 6 hydrocarbons, 1 ketone, 3 aldehydes, 2 nitrogen compounds, and 2 oxygen-containing compounds in jasmine; 29 terpenes, 6 alcohols, 28 esters, 8 nitrogen compounds, 1 aldehyde, and 6 other compounds in jasmine tea. The amounts of terpenes, esters, alcohols, nitrogen compounds, and hydrocarbons in jasmine and tea rose and then fell. The amount of oxygenated compounds of tea in the new scenting process first rose and then fell, while it showed a continuous upward trend during the traditional process. The amount of volatiles in jasmine and tea produced by the new scenting process were higher than that of the traditional scenting process at the same time. This study indicated that jasmine tea produced by the new scenting process had better volatile quality, which can provide proof for the new scenting process.

Most of the research on nanofluids focus on the heat/mass transfer or solar collection, while little consideration is given to the synergistic use of the properties of the nanoparticles themselves. Considering that the hybrid nanofluids are the key to realizing the multi-function of various nanoparticle characteristics, in this paper, an experimental system was built to study the combined applications of different nanofluids in the air refinement and heat recovery field. The results showed that the hybrid nanofluids have better long-term stable operating ability, the heat transfer efficiency of 0.01% TiO2-Ag nanofluids is increased by 1.033% compared with deionized water, and the concentrations of total volatile organic compounds and HCHO (formaldehyde) are reduced to 59.1 and 25.3 μg m−3, confirming the excellent heat recovery and air purification performance. Simultaneously, hybrid nanofluids also have good functions of removing PM2.5, PM10, and sterilization. It is expected that this study can guide the multifunctional usage of nanofluids technology in the field of air refinement and heat recovery. [ABSTRACT FROM AUTHOR]

As tea is one of the most popular beverages consumed worldwide, it is important for customers and business investigators to develop an easy and reliable method to discriminate between different types of teas from each other. A total of eighty-seven types of various white, green, oolong, black and Puer teas were collected from the major tea estates in China, and their catechin contents and volatile compounds were compared by high performance liquid chromatograph and gas chromatograph mass spectrometer. It was found green tea contained the highest concentrations of total catechins, (−)-epicatechin gallate (ECG) and (−)-epigallocatechin gallate (EGCG), while oolong teas contained the highest concentrations of (−)-epigallocatechin (EGC) among these five types of teas. The aroma composition and their quantities in different types of teas varied quite widely. The concentration of ECG, EGCG, pentanal, hexanal, methyl jasmonate, indole, (E,E)-2,4-hexadienal and 1,2,3-trimethoxybenzene was shown to be different and could be used to discriminate white, green, oolong, black and Puer teas. The result showed that different types of teas could be partially classified by cluster analysis using index of individual catechins and volatile components. [ABSTRACT FROM AUTHOR]