The effect of maturity of tea leaves and processing methods on the formation of milky flavor in white tea - A metabolomic study.

Targeted metabolomics combined with chemometrics were applied to investigate the flavor profiles of 4 white tea samples, which were produced from different maturity fresh tea leaves with different withering methods. Mature leaves that underwent novel withering process at higher temperature (28-30℃) and humidity (75 ± 3 %) (MN) were characterized by intense milky flavor. The content of free amino acids, catechins, and soluble sugars in MN were significantly lower than that in the other 3 tea samples, resulting in a sweet and mellow taste with low bitterness. Meanwhile, MN possessed the highest intensity of milky aroma, which could be mainly attributed to the existence of dihydro-5-pentyl-2(3H)-furanone and 2-pentyl-furan as the key volatile substances with coconut and creamy fragrance. These findings provide insight into the substance foundations of milky flavor, and identified leaf maturity and processing method as the determining factors of the milk-flavored white tea (MFWT).

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.

Impact of phenylalanine on Hanseniaspora vineae aroma metabolism during wine fermentation.

Hanseniaspora vineae exhibits extraordinary positive oenological characteristics contributing to the aroma and texture of wines, especially by its ability to produce great concentrations of benzenoid and phenylpropanoid compounds compared with conventional Saccharomyces yeasts. Consequently, in practice, sequential inoculation of H. vineae and Saccharomyces cerevisiae allows to improve the aromatic quality of wines. In this work, we evaluated the impact on wine aroma produced by increasing the concentration of phenylalanine, the main amino acid precursor of phenylpropanoids and benzenoids. Fermentations were carried out using a Chardonnay grape juice containing 150 mg N/L yeast assimilable nitrogen. Fermentations were performed adding 60 mg/L of phenylalanine without any supplementary addition to the juice. Musts were inoculated sequentially using three different H. vineae strains isolated from Uruguayan vineyards and, after 96 h, S. cerevisiae was inoculated to complete the process. At the end of the fermentation, wine aromas were analysed by both gas chromatography-mass spectrometry and sensory evaluation through a panel of experts. Aromas derived from aromatic amino acids were differentially produced depending on the treatments. Sensory analysis revealed more floral character and greater aromatic complexity when compared with control fermentations without phenylalanine added. Moreover, fermentations performed in synthetic must with pure H. vineae revealed that even tyrosine can be used in absence of phenylalanine, and phenylalanine is not used by this yeast for the synthesis of tyrosine derivatives.

Rapid classification of coffee origin by combining mass spectrometry analysis of coffee aroma with deep learning.

Mislabeling the geographical origin of coffee is a prevalent form of fraud. In this study, a rapid, nondestructive, and high-throughput method combining mass spectrometry (MS) analysis and intelligence algorithms to classify coffee origin was developed. Specifically, volatile compounds in coffee aroma were detected using self-aspiration corona discharge ionization mass spectrometry (SACDI-MS), and the acquired MS data were processed using a customized deep learning algorithm to perform origin authentication automatically. To facilitate high-throughput analysis, an air curtain sampling device was designed and coupled with SACDI-MS to prevent volatile mixing and signal overlap. An accuracy of 99.78% was achieved in the classification of coffee samples from six origins at a throughput of 1 s per sample. The proposed approach may be effective in preventing coffee fraud owing to its straightforward operation, rapidity, and high accuracy and thus benefit consumers.

Release characteristics and risk assessment of volatile sulfur compounds in a municipal wastewater treatment plant with odor collection device.

Due to the malodorous effects and health risks of volatile sulfur compounds (VSCs) emitted from wastewater treatment plants (WWTPs), odor collection devices have been extensively utilized; however, their effectiveness has rarely been tested. In the present investigation, the characteristics of VSCs released in a WWTP equipped with gas collection hoods are methodically examined by gas chromatography. The obtained results indicate that the concentration of VSCs in the ambient air can be substantially reduced, and the primary treatment unit still achieves the highest concentration of VSCs. Compared to WWTPs without odor collection devices, the concentration of H2S in this WWTP is not dominant, but its sensory effects and health risks are still not negligible. Additionally, research on the emission of VSCs from sludge reveals that the total VSCs emitted from dewatering sludge reaches the highest level. Volatile organic sulfur compounds play a dominant role in the component and sensory effects of VSCs released by sludge. This study provides both data and theoretical support for analyzing the effectiveness of odor collection devices in WWTPs, as well as reducing the source of VSCs. The findings can be effectively employed to optimize these devices and improve their performance.

Testing detectability, attractivity, hedonic specificity, extractability, and robustness of colostrum odor-Toward an olfactory bioassay for human neonates.

Human milk odor is attractive and appetitive for human newborns. Here, we studied behavioral and heart-rate (HR) responses of 2-day-old neonates to the odor of human colostrum. To evaluate detection in two conditions of stimulus delivery, we first presented the odor of total colostrum against water. Second, the hedonic specificity of total colostrum odor was tested against vanilla odor. Third, we delivered only the fresh effluvium of colostrum separated from the colostrum matrix; the stability of this colostrum effluvium was then tested after deep congelation; finally, after sorptive extraction of fresh colostrum headspace, we assessed the activity of colostrum volatiles eluting from the gas chromatograph (GC). Regardless of the stimulus-delivery method, neonates displayed attraction reactions (HR decrease) as well as appetitive oral responses to the odor of total colostrum but not to vanilla odor. The effluvium separated from the fresh colostrum matrix remained appetitive but appeared labile under deep freezing. Finally, volatiles from fresh colostrum effluvium remained behaviorally active after GC elution, although at lower magnitude. In sum, fresh colostrum effluvium and its eluate elicited a consistent increase in newborns' oral activity (relative to water or vanilla), and they induced shallow HR decrease. Newborns' appetitive oral behavior was the most reproducible response criterion to the effluvium of colostrum. In conclusion, a set of unidentified volatile compounds from human colostrum is robust enough after extraction from the original matrix and chromatographic processing to continue eliciting appetitive responses in neonates, thus opening new directions to isolate and assay specific volatile molecules of colostrum.

Exploring aromatic components differences and composition regularity of 5 kinds of these 4 aroma types Phoenix Dancong tea based on GC-MS.

Different aromatic components do indeed give different tea flavors. There is still little research on whether there is a certain regularity in the combination and content of aromatic components in different aroma types of Phoenix Dancong (PDC) tea. This potential regularity may be a key factor in unraveling the relationship between reproduction and evolution in PDC tea. Here, the 5 kinds of these 4 aroma types PDC tea (Zhuye, Tuofu, Jianghuaxiang, Juduo, Yashixiang) were used as research materials in this study, the headspace solid-phase microextraction combined with gas chromatography-mass spectrometry was used to analyze the aromatic components of these PDC teas. The results showed a total of 36 aromatic components identified in this study. When conducting cluster analysis, it was found that similarity degree arrangement sequence of 5 PDC teas was Juduo, Tuofu, Yashixiang, Zhuye and Jianghuaxiang. Among these aromatic components, the 7,9-Di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione, the 2-Cyclopenten-1-one, 3-methyl-2-(2-pentenyl)-,(Z)-, the 2,4-Di-tert-butylphenol, the 3,7-dimethyl-1,5,7-Octatrien-3-ol, and the 2-Furanmethanol,5-ethenyltetrahydro-.alpha.,.alpha.,5-trimethyl-,cis- are common to 5 PDC teas. This study aims to elucidate the similarities in the aromatic components of 5 PDC teas, revealing the major aroma-endowed substances of various aroma, and providing theoretical reference for further exploring the relationship between aroma type discrimination, variety selection, and evolution of PDC teas.

Artificial Intelligence Sensing: Effective Flavor Blueprinting of Tea Infusions for a Quality Control Perspective.

Tea infusions are the most consumed beverages in the world after water; their pleasant yet peculiar flavor profile drives consumer choice and acceptance and becomes a fundamental benchmark for the industry. Any qualification method capable of objectifying the product's sensory features effectively supports industrial quality control laboratories in guaranteeing high sample throughputs even without human panel intervention. The current study presents an integrated analytical strategy acting as an Artificial Intelligence decision tool for black tea infusion aroma and taste blueprinting. Key markers validated by sensomics are accurately quantified in a wide dynamic range of concentrations. Thirteen key aromas are quantitatively assessed by standard addition with in-solution solid-phase microextraction sampling followed by GC-MS. On the other hand, nineteen key taste and quality markers are quantified by external standard calibration and LC-UV/DAD. The large dynamic range of concentration for sensory markers is reflected in the selection of seven high-quality teas from different geographical areas (Ceylon, Darjeeling Testa Valley and Castleton, Assam, Yunnan, Azores, and Kenya). The strategy as a sensomics-based expert system predicts teas' sensory features and acts as an AI smelling and taste machine suitable for quality controls.

Exploration of Raw Pigmented-Fleshed Sweet Potatoes Volatile Organic Compounds and the Precursors.

Sweet potato provides rich nutrients and bioactive substances for the human diet. In this study, the volatile organic compounds of five pigmented-fleshed sweet potato cultivars were determined, the characteristic aroma compounds were screened, and a correlation analysis was carried out with the aroma precursors. In total, 66 volatile organic compounds were identified. Terpenoids and aldehydes were the main volatile compounds, accounting for 59% and 17%, respectively. Fifteen compounds, including seven aldehydes, six terpenes, one furan, and phenol, were identified as key aromatic compounds for sweet potato using relative odor activity values (ROAVs) and contributed to flower, sweet, and fat flavors. The OR sample exhibited a significant presence of trans-ß-Ionone, while the Y sample showed high levels of benzaldehyde. Starch, soluble sugars, 20 amino acids, and 25 fatty acids were detected as volatile compounds precursors. Among them, total starch (57.2%), phenylalanine (126.82 ± 0.02 g/g), and fatty acids (6.45 µg/mg) were all most abundant in Y, and LY contained the most soluble sugar (14.65%). The results of the correlation analysis revealed the significant correlations were identified between seven carotenoids and trans-ß-Ionone, soluble sugar and nerol, two fatty acids and hexanal, phenylalanine and 10 fatty acids with benzaldehyde, respectively. In general, terpenoids and aldehydes were identified as the main key aromatic compounds in sweet potatoes, and carotenoids had more influence on the aroma of OR than other cultivars. Soluble sugars, amino acids, and fatty acids probably serve as important precursors for some key aroma compounds in sweet potatoes. These findings provide valuable insights for the formation of sweet potato aroma.

Metabolomics analysis of flavor differences in Shuixian (Camellia sinensis) tea from different production regions and their microbial associations.

Shuixian is renowned for its "rock flavor". However, the variations in Shuixian flavor are unclear, as the discussion mainly considers regional factors and overlooks the role of microorganisms. Sensory evaluation of Shuixian from three different regions (Zhengyan, Banyan, and Waishan) revealed that each had unique flavor characteristics: a woody aroma with slight acidity, a strong floral and fruity aroma with good freshness, and a distinct sweet aroma and sourness. Metabolomic analyses have revealed that 2-methylpyrazine was a crucial component of the woody aroma, whereas other metabolites contributed to sweet aroma, freshness, and acidity. Moreover, examinations of the relationship between flavor metabolites and microorganisms revealed that fungi had a more pronounced influence on the metabolite content of Shuixian. The study evaluated the role of fermentation microorganisms in shaping the flavor based on Shuixian flavor analyses, contributing to further research into the "rock flavor", as well as potential microbial interventions.

Effects of Monascus purpureus on ripe Pu-erh tea in different fermentation methods and identification of characteristic volatile compounds.

The present study aimed to explore the key volatile compounds (VCs) that lead to the formation of characteristic flavors in ripe Pu-erh tea (RIPT) fermented by Monascus purpureus (M. purpureus). Headspace solid-phase microextraction coupled with gas chromatography/mass spectrometry (HS-SPME-GC-MS), orthogonal partial least square-discriminant analysis (OPLS-DA) were employed for a comprehensive analysis of the VCs present in RIPT fermented via different methods and were further identified by odor activity value (OAV). The VCs 1,2-dimethoxybenzene, 1,2,3-trimethoxybenzene, (E)-linalool oxide (pyranoid), methyl salicylate, linalool, ß-ionone, ß-damascenone were the key characteristic VCs of RIPT fermented by M. purpureus. OAV and Gas chromatography-olfactometry (GC-O) further indicated that ß-damascenone was the highest contribution VCs to the characteristic flavor of RIPT fermented by M. purpureus. This study reveals the specificities and contributions of VCs present in RIPT under different fermentation methods, thus providing new insights into the influence of microorganisms on RIPT flavor.

Evaluation of spontaneous fermentation impact on the physicochemical properties and sensory profile of green and roasted arabica coffee by digital technologies.

There is a growing demand for specialty coffee with more pleasant and uniform sensory perception. Wet fermentation could modulate and confer additional aroma notes to final roasted coffee brew. This study aimed to assess differences in volatile compounds and the intensities of sensory descriptors between unfermented and spontaneously fermented coffee using digital technologies. Fermented (F) and unfermented (UF) coffee samples, harvested from two Australia local farms Mountain Top Estate (T) and Kahawa Estate (K), with four roasting levels (green, light-, medium-, and dark-) were analysed using near-infrared spectrometry (NIR), and a low-cost electronic nose (e-nose) along with some ground truth measurements such as headspace/gas chromatography-mass spectrometry (HS-SPME-GC-MS), and quantitative descriptive analysis (QDA ®). Regression machine learning (ML) modelling based on artificial neural networks (ANN) was conducted to predict volatile aromatic compounds and intensity of sensory descriptors using NIR and e-nose data as inputs. Green fermented coffee had significant perception of hay aroma and flavor. Roasted fermented coffee had higher intensities of coffee liquid color, crema height and color, aftertaste, aroma and flavor of dark chocolate and roasted, and butter flavor (p < 0.05). According to GC-MS detection, volatile aromatic compounds, including methylpyrazine, 2-ethyl-5-methylpyrazine, and 2-ethyl-6-methylpyrazine, were observed to discriminate fermented and unfermented roasted coffee. The four ML models developed using the NIR absorbance values and e-nose measurements as inputs were highly accurate in predicting (i) the peak area of volatile aromatic compounds (Model 1, R = 0.98; Model 3, R = 0.87) and (ii) intensities of sensory descriptors (Model 2 and Model 4; R = 0.91), respectively. The proposed efficient, reliable, and affordable method may potentially be used in the coffee industry and smallholders in the differentiation and development of specialty coffee, as well as in process monitoring and sensory quality assurance.

Effect of industrial wastewater treatment system upgrade on the composition of emitted odorants and volatile organic compounds from a cheese production facility.

This study investigates the rarely studied volatile organic compound emissions from a cheese production facility and the impact of its wastewater treatment system upgrade on the composition of emitted odorants. Wastewater grab samples were collected from six separate wastewater channels before (2019) and after (2021) the system upgrade and analyzed for volatile organic compounds, pH, total dissolved solids, and electrical conductivity. Results showed that the channel from hard cheese production in 2021 had the highest number of volatile organic compounds (35), followed by the fresh cheese production channel (22). Following the industrial wastewater treatment system upgrade, a mineral oil contamination occurred; however, the number of odorants with nasal impact frequency (NIF) ≥ 0.5 in the effluent decreased from 11 to 5. 2-Propenoic acid butyl ester (NIF 0.75) stood out as the most prominent compound, described as fruity, waxy, or green. After the industrial wastewater treatment system upgrades, we observed a decrease in the number of odorants. However other measures must be taken to ensure proper wastewater processing. PRACTITIONER POINTS: More than 60 VOCs were identified in 6 channels from the cheese production facility.15 odorants in cheese production wastewater were detected by SPME-GC-MS/O. The most potent odorants before and after the system upgrade were 1-octen-3-ol and 2-propenoic acid butyl ester, respectively. The upgrades of the industrial wastewater treatment system had a positive impact on reducing the number of odorants and their odor intensity.

Unraveling the contributing factors of stale odor in Longjing tea through a sensomics approach.

Longjing tea is renowned for its fresh aroma and high value. However, during storage, the emergence of an off-flavor known as "stale odor" can significantly impact the flavor quality and economic benefits of Longjing tea. Yet, the specific volatiles responsible for this stale odor in Longjing tea remain unknown. In this study, Longjing tea samples with varying degrees of stale odor intensity were analyzed using simultaneous distillation extraction coupled with gas chromatography-mass spectrometry (SDE-GC-MS). Through odor activity value (OAV) and fractional omission testing, hexanoic acid and trans-2-nonenal were identified as the primary contributors to the stale odor. Moreover, the concentration of hexanoic acid was found to be valuable in predicting the intensity of the stale odor in Longjing tea. The oxidative degradation of linoleic acid was proved as the generation pathway of stale odor in Longjing tea. These findings provide essential theoretical principles for Longjing tea production and preservation.

Aroma and taste analysis of pickled tea from spontaneous and yeast-enhanced fermentation by mass spectrometry and sensory evaluation.

Anaerobically fermented pickled tea (PT) can be produced by spontaneous fermentation (SF) or yeast-enhanced fermentation (YF). Aroma and taste characteristics of PT during YF and SF were investigated using sensory evaluation, odour activity, aroma character impact values, HS-SPME-GC-MS, UPLC-QQQ-MS/MS, and spectrophotometry, annotating 198 volatile and 115 non-volatile components. The main contributing volatile components were ß-ionone, and 1-octanol, promoted by YF and SF, and yielding floral and fruity aromas respectively. Additionally, compared with SF, YF promoted the formation of citronellol yielding a floral aroma, inhibited the stale aroma of methoxybenzenes, and reduced bitter, astringent, and sour tastes. Furthermore, partial least-squares regression analysis identified the main components related to the 'acides aroma' of PT as linalool oxide, n-decanoic acid, hexanoic acid, 3,7-dimethyl-2,6-octadienoic acid, 3-methyl-1-dodecyn-3-ol, and nerolidol. This application could be used as methodology for the comprehensive analysis of tea aroma and taste and these results can act as guidelines for PT production and quality control.

The key aroma components of steamed green tea decoded by sensomics and their changes under different withering degree.

Steamed green tea has a long history and unique aroma, but little is known about its key aroma components. In this study, 173 volatiles in steamed green tea were identified using solvent-assisted flavor evaporation and headspace-solid phase microextraction plus two chromatographic columns of different polarities. Aroma extract dilution analysis revealed 48 highly aroma-active compounds with flavor dilution factors 64-1024. Internal standards were used to calculate odorant active value (OAV), and 11 OAV > 1 key aroma compounds were determined. Omission test identified eight substances, including dimethyl sulfide, (E)-ß-ionone, cis-jasmone, linalool, nonanal, heptanal, isovaleraldehyde and (Z)-3-hexenol, as the key aroma active compounds of steamed green tea. With the increase of withering degree, the content of these substances increased first and then decreased except for heptanal and cis-jasmone. Moreover, the water content of 62 % was suggested to be an appropriate withering degree during the processing of steamed green tea.

Study on color, aroma, and taste formation mechanism of large-leaf yellow tea during an innovative manufacturing process.

This study used samples processed with an innovative manufacturing process to explore the dynamic changes of large-leaf yellow tea (LYT) in color, aroma, and taste substances, and the quality components were most significantly affected in the stages of first pile-yellowing (FP) and over-fired drying (TD). In this process, the moisture and temperature conditions caused chlorophyll degradation, Maillard reactions, caramelization reactions, and isomerization of phenolic substances, forming the quality of LYT. Specifically, chlorophyll degradation favored the formation of color quality; the taste quality was determined by the content of soluble sugars, amino acids, catechins, etc.; the aroma quality was dependent on the content changes of alcohols and aldehydes, as well as the increase of sweet and roasting aroma substances in the third drying stage. Additionally, twelve key aroma components, including linalool, (E)-ß-ionone, 2,3-diethyl-5-methyl-pyrazine, etc., were identified as contributors to revealing LYT rice crust-like and sweet aroma formation mechanism.

Effect of enzymatic Maillard reaction conditions on physicochemical properties, nutrition, fatty acids composition and key aroma compounds of fragrant rapeseed oil.

BACKGROUND: A new enzymatic hydrolysis-based process inspired by the Maillard reaction can produce strong flavored, high-value rapeseed oil that meets safety requirements. In the present study, the effect of reaction time (10-30 min) and temperature (130-160 °C) on the physicochemical properties, nutritional status, fatty acids composition and key aroma compounds of fragrant rapeseed oil (FRO) was investigated. RESULTS: An increasing reaction time and temperature substantially decreased the total tocopherol, polyphenol and sterol contents of FRO, but increased benzo[a]pyrene content, as well as the acid and peroxide values, which did not exceed the European Union legislation limit. Among the volatile components, 2,5-dimethyl was the main substance contributing to the barbecue flavor of FRO. The 150 °C for 30 min reaction conditions produced a FRO with a strong, fragrant flavor, with high total tocopherol (560.15 mg kg-1 ), polyphenol (6.82 mg kg-1 ) and sterol (790.65 mg kg-1 ) contents; acceptable acid (1.60 mg g-1 ) and peroxide values (4.78 mg g-1 ); and low benzo[a]pyrene (1.39 mg g-1 ) content. These were the optimal conditions for the enzymatic Maillard reaction, according to the principal component analysis. Furthermore, hierarchical cluster analysis showed that reaction temperature had a stronger effect on FRO than reaction time. CONCLUSION: The optimal enzymatic Maillard reaction conditions for the production of FRO are heating at 150 °C for 30 min. These findings provide new foundations for better understanding the composition and flavor profile of FRO, toward guiding its industrial production. © 2023 Society of Chemical Industry.

Monitoring the dynamic changes in aroma during the whole processing of Qingzhuan tea at an industrial scale: From fresh leaves to finished tea.

Aroma is one of the most outstanding quality characteristics of Qingzhuan tea (QZT), but its formation is still unclear. Thus, the volatile organic compounds (VOCs) during the whole processing of QZT were investigated by headspace solid-phase microextraction/gas chromatography-mass spectrometry. Based on 144 identified VOCs, the results showed that de-enzyming, sun-drying, and piling fermentation were the key processes of QZT aroma formation. Furtherly, 42 differential VOCs (VIP > 1.0 and p < 0.05) and 16 key VOCs (rOAV > 1.0 and/or ROAV > 1.0) were screened. Especially, sulcatone and ß-ionone (rOAV > 100 and ROAV > 10) were considered the most important contributors to the aroma of QZT. The metabolisms of key VOCs were mainly involved in oxidative degradation of fatty acids, degradation of carotenoids, and methylation of gallic acid. This study could help to more comprehensively understand the aroma formation in QZT processing at an industrial scale.

Moisture content of tea dhool for the scenting process affects the aroma quality and volatile compounds of osmanthus black tea.

To improve the quality of osmanthus black tea, samples produced with different scenting methods were prepared. The sensory quality was assessed and the characteristic aromatic components were explored using solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry. According to the results, osmanthus black tea obtained by adding osmanthus scenting in the fermentation process had the strongest floral aroma. The major contributors to the aroma of osmanthus black tea were identified as ß-ionone, dihydro-ß-ionone, benzeneacetaldehyde, citral, geraniol, and linalool by calculating their relative odor activity values. An analysis of the causes revealed that the moisture content of tea dhool significantly affected the adsorption of fresh flower aroma by tea. The experimental results showed that osmanthus black tea produced using tea dhool containing 30% moisture content had the highest content of crucial aroma components, suggesting the tea dhool under this condition had the strongest adsorption capacity for osmanthus aroma.