2-phenylethyl Acetate Research Articles

Volatile Metabolism of Wine Grape Trincadeira: Impact of Infection with Botrytis cinerea.

The aroma of grapes is cultivar dependent and is influenced by terroir, vineyard practices, and abiotic and biotic stresses. Trincadeira is a non-aromatic variety associated with low phenolic content and high sugar and organic acid levels. This cultivar, widely used in Portuguese wines, presents high susceptibility to Botrytis cinerea. This work aimed to characterise the volatile profile of Trincadeira grapes and how it changes under infection with B. cinerea. Thirty-six volatile organic compounds were identified, from different functional groups, namely alcohols, ester acetates, fatty acid esters, fatty acids, aldehydes, and products of the lipoxygenase pathway. Both free and glycosidic volatile organic compounds were analysed by Gas Chromatography and Gas Chromatography coupled to Mass Spectrometry for component quantification and identification, respectively. A multivariance analysis showed a clear discrimination between healthy and infected grapes with 2-trans-hexenal and isoamyl-acetate among the compounds identified as negative and positive markers of infection, respectively. Ester acetates such as 2-phenylethyl acetate, isoamyl acetate, and 2-methylbutyl acetate were present in higher contents in infected samples, whereas the contents of several fatty acid esters, such as ethyl decanoate and ethyl dodecanoate, decreased. These data were integrated with quantitative PCR data regarding genes involved in volatile metabolism and showed up-regulation of a gene coding for Hydroperoxide Lyase 2 in infected grapes. Altogether, these changes in volatile metabolism indicate an impact on the grape quality and may be related to defence against B. cinerea. The presence/absence of specific compounds might be used as infection biomarkers in the assessment of Trincadeira grapes’ quality.

Study on Synthesis of 1-Phenylethyl Acetate by Enzymatic Kinetic Resolution

Study on Synthesis of 1-Phenylethyl Acetate by Enzymatic Kinetic Resolution

Chemical and sensory characterization of Kalecik Karası wines produced from two different regions in Turkey using chemometrics

Kalecik Karası (KK) is one of the important native grape varieties of Turkey used in red wine production. As an extension of a previous project that profiled the sensory characteristics of KK wines from different geographic regions of Turkey, this study aimed to investigate the chemical composition and sensory properties of KK wines belonging to different vintages from two different regions (Kalecik/Ankara and Güney/Denizli) using the chemometric technique. Identification and quantification of aroma, aroma-active compounds, and sensory evaluations were carried out by GC/MS/FID, GC-O, and Descriptive Analyses. PLSR was used for determining the correlation between chemical and sensory data. A total of 26 aroma-active compounds have been identified for both regions. Based on PLSR, red fruit attribute in wines was positively correlated with isoamylacetate, ethyl-hexadecanoate, ethyl-4-hydroxybutanoate, and 2-phenylethyl acetate. Dried fruit attribute has shown a significant positive correlation with ethyl-2-methyl-propanoate, ethyl-2-methylbutanoate, and ethyl-3-methylbutanoate. The cotton candy attribute was positively correlated with 2-phenylethanol, 2-phenylethyl acetate, ethyl-4-hydroxybutanoate, and gamma-butyrolactone. Novelty impact statement This is the first study in the literature to determine the correlation between chemical and sensory data in Kalecik Karası wines. The study determined that common aroma descriptors of KK wines include red fruit (strawberry, raspberry, and apple), dried fruit, cotton candy, flower, and spice (sweet spices and nutmeg) odors. The characterization of the wines using chemometrics is an important tool. The findings obtained may constitute a source for quality Kalecik Karası wines in transition to the Geographical Indication system.

Screening and Identification of Yeasts from Fruits and Their Coculture for Cider Production

Coculturing non-Saccharomyces yeasts with Saccharomyces cerevisiae could enrich the aromatic complexity of alcoholic beverages during cider brewing. Therefore, the present study performed rapid strain screening via selective culture medium and aroma analysis and adopted a response surface methodology to optimize fermentation conditions to produce 2-phenylethyl acetate (PEA), which presents a rose and honey scent. The effects of coculturing yeasts on cider quality were evaluated through hedonic sensory analysis and the check-all-that-apply (CATA) method. Hanseniaspora vineae P5 and S. cerevisiae P1 produced ciders with high levels of PEA and 2-phenylethanol, respectively. The optimal fermentation process consisted of sequential inoculation with a 31 h delay between inoculations, followed by fermentation for 14.5 d at 18.7 °C, yielding 17.41 ± 0.51 mg/L of PEA, which was 4.6-fold higher than that obtained through the unoptimized fermentation process. Additionally, the CATA results revealed that the cider produced through coculturing was associated with descriptors such as “smooth taste”, “honey”, “pineapple”, and “fruity”, which can be attributed to the high ethyl acetate and PEA levels in the cider.

Influence of Kazachstania spp. on the chemical and sensory profile of red wines

We report the fermentative traits of two Kazachstania species (K. aerobia and K. servazzii) in non-sterile red wine and the resulting chemical and sensory properties. This builds on our previous work which revealed that Kazachstania spp. increased acetate esters in sterilised white wine. In this study Kazachstania spp. were initially evaluated in laboratory-scale fermentations (500 mL) in Merlot must to assess whether similar increases in chemical/volatile compounds would occur. The impact of malolactic fermentation (MLF) by Oenococcus oeni (VP41) on aroma composition was considered and found to reduce ester profiles in Merlot wines. The sensory implications of sequential inoculation with Kazachstania spp., followed by Saccharomyces cerevisiae, were then evaluated in small-lot fermentations (7 kg) of Shiraz must. Fungal diversity was monitored during early fermentation stages and was influenced by the early implantation of Kazachstania spp., followed by the dominance of S. cerevisiae. The effect of MLF in Shiraz wines was inconclusive due to high ethanol levels providing an inhospitable environment for lactic acid bacteria. When compared to S. cerevisiae alone, Kazachstania spp. significantly increased acetate esters, particularly phenylethyl acetate and isoamyl acetate, in both Merlot and Shiraz. The Shiraz wines fermented with Kazachstania spp. had higher jammy and red fruit aroma/flavour compared to S. cerevisiae (monoculture) wines. No influence was observed on colour one-year post-bottling. Results from this study show the contribution of Kazachstania spp. to the aroma profile of red wines and demonstrate their potential as starter cultures for improving the aromatic complexity of wines.

Nonconventional yeasts to produce aroma compounds by using agri-food waste materials.

Nowadays, biotechnological applications are emphasized to ensure sustainable development by reutilizing waste materials to prevent ecological problems and to produce or recover compounds that may have positive effects on health. Yeasts are fascinating microorganisms that play a key role in several traditional and innovative processes. Although Saccharomyces is the most important genus of yeasts, and they are major producers of biotechnological products worldwide, a variety of other yeast genera and species than Saccharomyces that are called 'non-Saccharomyces' or 'nonconventional' yeasts also have important potential for use in biotechnological applications. Some of the nonconventional yeast strains offer a unique potential for biotechnological applications to produce valuable secondary metabolites due to their characteristics of surviving and growing in such extreme conditions, e.g. wide substrate range, rapid growth, thermotolerance, etc. In this review, we aimed to summarize potential biotechnological applications of some nonconventional yeasts (Kluyveromyces spp., Yarrowia spp., Pichia spp., Candida spp., etc.) to produce industrially important aroma compounds (phenylethyl alcohol, phenylethyl acetate, isobutyl acetate, diacetyl, etc.) by reutilizing agri-food waste materials in order to prevent ecological problems and to produce or recover compounds that may have positive effects on health.

“Portugizac Mlado vino”; is the aroma of younger red wine more attractive?

“Portugizac Mlado vino” is a local red wine with Protected designation of origin and Traditional term, and it is usually consumed very soon after alcoholic fermentation as a young wine. The maturation and aging of the wine affect the aroma composition, which is generally not pronounced and specific in the case of most red wines, but, as a sensory property, it is important for the perception of quality and consumer choice. The objective of this work was to analyze the most important aroma compounds of esters and higher alcohols, with the unpleasant volatile phenols too, in “Portugizac” wines, related to aging. The 9 young wines “Portugizac”, PDO “Plešivica” were analyzed after 3 and after 15 months of bottle storage at 16 ºC. Ethyl esters of butanoic and hexanoic acid along with isoamyl acetate are considered to be the most important esters in the fruity aroma of wine, and their concentrations in all analyzed “Portugizac” young wine samples were higher than their perception thresholds. The concentration of ethyl acetate was in the range 30-123 mg/L. The concentrations of ethyl esters of octanoic and decanoic acid, as well as 2-phenyl ethyl acetate and diethyl succinate in all analyzed wines, were lower than their perception thresholds. The concentrations of higher alcohols were much higher than their perception threshold. Bottle storage significantly affected the concentrations of analyzed compounds; after 15 months, the concentrations of acetate and ethyl esters (except ethyl acetate and diethyl succinate), as well as terpene (linalool), decreased, while higher alcohols and ethyl phenols slightly increased if compared to three months. In general, the compounds responsible for the desired fresh, fruity aroma tones were altered in an undesirable manner, while, undesirable compounds of 4-ethyl-phenol and 4-ethyl-quaiacol, which were not present in young wines, were detected in aged wines. It can be concluded that the bottle aging affects the aroma profile, undesirable changes were more pronounced than positive ones and therefore the consumption of young wine “Portugizac” might be more sensory attractive.

Metabolic flux sampling predicts strain-dependent differences related to aroma production among commercial wine yeasts

BackgroundMetabolomics coupled with genome-scale metabolic modeling approaches have been employed recently to quantitatively analyze the physiological states of various organisms, including Saccharomyces cerevisiae. Although yeast physiology in laboratory strains is well-studied, the metabolic states under industrially relevant scenarios such as winemaking are still not sufficiently understood, especially as there is considerable variation in metabolism between commercial strains. To study the potential causes of strain-dependent variation in the production of volatile compounds during enological conditions, random flux sampling and statistical methods were used, along with experimental extracellular metabolite flux data to characterize the differences in predicted intracellular metabolic states between strains.ResultsIt was observed that four selected commercial wine yeast strains (Elixir, Opale, R2, and Uvaferm) produced variable amounts of key volatile organic compounds (VOCs). Principal component analysis was performed on extracellular metabolite data from the strains at three time points of cell cultivation (24, 58, and 144 h). Separation of the strains was observed at all three time points. Furthermore, Uvaferm at 24 h, for instance, was most associated with propanol and ethyl hexanoate. R2 was found to be associated with ethyl acetate and Opale could be associated with isobutanol while Elixir was most associated with phenylethanol and phenylethyl acetate. Constraint-based modeling (CBM) was employed using the latest genome-scale metabolic model of yeast (Yeast8) and random flux sampling was performed with experimentally derived fluxes at various stages of growth as constraints for the model. The flux sampling simulations allowed us to characterize intracellular metabolic flux states and illustrate the key parts of metabolism that likely determine the observed strain differences. Flux sampling determined that Uvaferm and Elixir are similar while R2 and Opale exhibited the highest degree of differences in the Ehrlich pathway and carbon metabolism, thereby causing strain-specific variation in VOC production. The model predictions also established the top 20 fluxes that relate to phenotypic strain variation (e.g. at 24 h). These fluxes indicated that Opale had a higher median flux for pyruvate decarboxylase reactions compared with the other strains. Conversely, R2 which was lower in all VOCs, had higher median fluxes going toward central metabolism. For Elixir and Uvaferm, the differences in metabolism were most evident in fluxes pertaining to transaminase and hexokinase associated reactions. The applied analysis of metabolic divergence unveiled strain-specific differences in yeast metabolism linked to fusel alcohol and ester production.ConclusionsOverall, this approach proved useful in elucidating key reactions in amino acid, carbon, and glycerophospholipid metabolism which suggest genetic divergence in activity in metabolic subsystems among these wine strains related to the observed differences in VOC formation. The findings in this study could steer more focused research endeavors in developing or selecting optimal aroma-producing yeast stains for winemaking and other types of alcoholic fermentations.

Effect of co-inoculation and sequential inoculation of Lactobacillus fermentum and Pichia kluyveri on pork hydrolysates fermentation

This is the first study on exploiting a LAB - Lactobacillus fermentum PCC and a yeast Pichia kluyveri (FrootZen) as starter cultures in meat-based sauce fermentation. An apparent antagonistic relationship was observed between these two cultures. P. kluyveri proliferated with an increased cell count of only 1.14 log CFU/mL and dropped to the original level (approx. 5.8 log CFU/mL), while the LAB growth was stimulated by increasing the cell count by 1.67 log CFU/mL in simultaneous inoculation. More pleasant fruity aromatic esters such as hexyl acetate and 2-phenylethyl acetate were detected in the sequential inoculation, while more acetic acid was detected in the simultaneous inoculation. However, there were no significant differences (P ≥ 0.05) in the glucose usage, production of organic acids, and amino acids in the fermented pork hydrolysates between these two inoculation methods.

Rational Selection of Mixed Yeasts Starters for Agave Must Fermentation

Tequila and mezcal are both traditional Mexican liquors that are produced from cooked Agave spp. must fermentation and usually rely on spontaneous or pure Saccharomyces cerevisiae strain inoculation. In order to contribute to the rational selection of yeast starters for tequila and mezcal productions, we tested a collection of 25 yeasts originally isolated from mezcal musts, spanning 10 different yeast species. These strains were first characterized in a semi synthetic medium (labeled as M2, having 90 g/L fructose and 10 g/L glucose of initial hexoses) at 48 h of culture, observing a differential pattern in the consumption of sugars and productivity. Selected Saccharomyces strains left around 10 g/L of fructose and showed higher fermentation performance. However, some non-Saccharomyces strains, specifically from Torulospora (Td), Kluyveromyces (Km), and Zygosaccharomyces (Zb) genera, consumed almost all the sugar (i.e., Km1Y9 with <5 g/L) and had a high productivity of ethanol. In general, all Saccharomyces strains presented a high production of ethyl-butyrate, ethyl-decanoate, and ethyl-hexanoate with peaks of 10, 38, and 3 μg/L, respectively. In addition, some Kluyveromyces and Torulospora strains showed a high production of phenyl ethyl acetate (i.e., Km1D5 with up to 1400 μg/L); isoamyl acetate (i.e., Km1D5 and Td1AN2 with more than 300 μg/L), and hexyl acetate (i.e., Td1AN2 with 0.3 μg/L). Representative strains of the most productive genera (Saccharomyces, Torulospora, and Kluyveromyces) were selected to evaluate their fermentative performance and survival in a mixed culture on a medium based on Agave tequilana must, and their population kinetics was characterized using specific fluorescent in situ hybridization (FISH) probes in a qualitative and semi-quantitative analysis during fermentation. We observed that the mixture ratios of 0.1:1:1 or 1:1:1 (Saccharomyces:Kluyveromyces:Torulospora), maintained good fermentation productivities, with alcohol yields above 0.45 g/g, and allowed a high survival rate of the non-Saccharomyces strains during the fermentation process. Finally, mixed inoculum fermentations on A. tequilana must medium, including different Saccharomyces strains and the finally selected Torulospora and Kluyveromyces strains, showed the best production parameters in terms of ethanol, carbon dioxide, glycerol, and acetic acid values, as well as improved volatile metabolite profiles as compared to the pure cultures. All these data were used to propose a methodology of selection of strains to be used as a pure or mixed starter for tequila and mezcal fermentations, with high primary metabolite productivity and desired aromatic profile.

Tasting the Italian Terroir through Craft Beer: Quality and Sensory Assessment of Cascade Hops Grown in Central Italy and Derived Monovarietal Beers.

The present study aimed to chemically and sensorially characterize hop samples, cv Cascade, grown in two different Italian regions (Latium and Tuscany) as well as their derived beers by a multi analytical approach. Significant differences in bitter acid, oil and polyphenol content were observed for hop samples according to their origin. Gas chromatography-olfactometry analysis pointed out floral notes for Tuscany samples, where hops from Latium were characterized by spicy and resinous notes, correlated to the presence of sesquiterpenes. Differences in the molecular fingerprinting were also highlighted by Fourier–Transform Infrared Spectroscopy. The differences found in the hops were reflected in the beers, which were clearly recognized as distinct by a sensory panel. Both beer samples were mainly characterized by six aroma compounds (linalool, geraniol and β-damascenone, citronellol, 2-phenylethyl acetate, and 2-phenylethanol), three of which were potentially responsible for the geographic origin of the hops given their significantly different concentrations.

Bioprospecting of indigenous yeasts involved in cocoa fermentation using sensory and chemical strategies for selecting a starter inoculum

Cocoa fermentation is the key and most relevant process in the synthesis of aroma and flavor precursor molecules in dry beans or raw material for producing chocolate. Because this process occurs in an uncontrolled manner, the chemical and sensory quality of beans can vary and be negatively affected. One of the strategies for the standardization and improvement of the sensory quality of chocolate is the introduction of microbial starter cultures. Among these, yeasts involved in fermentation have been studied because of their pectinolytic and metabolic potential in the production of volatile compounds. This study was aimed at isolating and characterizing, both sensory and chemically, yeasts involved in cocoa fermentation that could be used as starter cultures from two agro-ecological regions for the cultivation of cocoa in Colombia. The microbiological analyses identified 22 species represented mostly by Saccharomyces cerevisiae, Wickerhamomyces anomalus and Pichia sp. The preliminary sensory analysis of eight of these species showed that Hanseniaspora thailandica and Pichia kluyveri presented sensory profiles characterized by high intensity levels of fruity notes, which could be ascribed to the production of ethyl acetate, isoamyl acetate, and 2-phenylethyl acetate.

Antioxidant capacity, phytochemical compounds, and volatile compounds related to aromatic property of vinegar produced from black rosehip (Rosa pimpinellifolia L.) juice

Black rosehip (Rosa pimpinellifolia L.) is an edible fruit belonging to the large Rosaceae family. Processing this and similar fruits that have low water into vinegar generates added values. Besides, vinegar consumption has beneficial effects on human health. This study aimed to produce vinegar with enormous functional properties from the black rosehip fruits, which is disadvantaged due to its low water content, and high functional activities, and to convert from this fruit into a high value-added product. As a result, it was showed that the wine and vinegar had higher values of antioxidant activities than the juice; however, the highest values of total phenolic content, total anthocyanin content, total flavonoid content, and antioxidant activity were found in the wine. Gallic acid, catechin, ellagic acid, protocatechuic acid, and epicatechin were the most important bioactive compounds in wine and vinegar. Vitamin-C content increased significantly in the vinegar, giving a positive feature to the vinegar. Especially, the vinegar stood out in terms of volatile aroma compounds, including a total of 28 volatile compounds whose major components were 2-phenylethanol, acetic acid, octanoic acid, ethyl acetate, phenylethyl acetate, and 3-methyl-1-butanol. Also, hexyl-salicylate, 4-terpineol, and dihydro-methyl jasmonate. The present study showed the richness of black rosehip vinegar in aroma compounds and functional aspects. Black rosehip fruit was revealed to be a suitable raw material mainly for vinegar production. A new product was obtained to take advantage of the enormous antioxidant activity of black rosehip fruit, which has limited consumable and processability due to its low water content.

Characterization of the flavor and nutritional value of coconut water vinegar based on metabolomics

Tender Coconut water is popular for its deliciousness and nutrition. Mature coconut water, usually discarded as waste in the coconut kernel-based food industry due to its unpleasant flavor, was used as a raw material to make vinegar by liquid-state fermentation. The compounds in fresh coconut water with high odor activity values (OAVs) were isovaleric acid and acetic acid, with pungent sour tastes. The compounds with high OAVs in aged coconut water vinegar were phenylethyl acetate, isoamyl acetate and benzaldehyde, with almond, banana or pear-like aromas. Coconut water vinegar was rich in essential amino acids, especially phenylalanine. Through pathway analysis, seventeen key metabolic pathways and three key metabolic substrates (aspartate, glutamate and pyruvate) were found. According to sensory evaluation, the aged vinegar tastes better. Coconut water vinegar is delicious and nutritious, so reprocessing mature coconut water into vinegar is an appropriate way to reuse waste coconut water.

Volatile composition and sensory properties of wines from vineyards affected by iron chlorosis

Recent studies have shown that mild to moderate iron chlorosis can have positive effects on grape quality potential, including volatile profile. The main objective of this work was to investigate, for the first time, how moderate iron stress in grapevines affects the presence of volatile organic compounds (VOCs) in wines. The study was carried out during 2018–2019 seasons, in 20 Tempranillo vineyard subzones with different degree of iron deficiency, located in Ribera del Duero (North-Central Spain). The results showed that moderate iron stress increased in wines the concentrations of VOCs associated with floral notes, such as 2-phenylacetaldehyde, 2-phenylethanol and 2-phenylethyl acetate, while reducing the presence of C6-alcohols, responsible for green-herbaceous aroma.A favourable reduction of pH and a betterment of parameters related to colour were detected in wines from iron deficient subzones. Chlorosis incidence was associated to improvements in wine sensory attributes as layer intensity, black fruit and aroma intensity.

Application of Hanseniaspora vineae Yeast in the Production of Rosé Wines from a Blend of Tempranillo and Albillo Grapes

Hanseniaspora vineae is an apiculate yeast that can be used for the production of interesting commercial wines, due to its contribution of fermentative volatiles. This paper presents a detailed comparative study of the use of H. vineae, compared to pure fermentations of S. cerevisiae in Tempranillo and Albillo rosé wines. Fermentations were carried out in oak barrels and stainless steel barrels. The results indicated that fermentation with H. vineae resulted in wines with residual sugars below 3.4 g/L and similar general characteristics, compared to S. cerevisiae. However, H. vineae wines contain up to 44% more total anthocyanins, resulting in an appreciable improvement in colour. In addition, H. vineae produced up to 65% more 2-phenylethyl acetate in stainless steel barrels and 2.5 times more terpene alcohols in oak barrels. Therefore, the use of H. vineae results in a more attractive colour, as well as fruity and floral organoleptic characteristics of rosé wines.

Self‐healing in high impact polystyrene (HIPS) composites via embedded non‐toxic solvent‐filled microcapsules

AbstractPolymer composites are widely used in many industries due to their desirable, and commonly superior properties. However, the replacement of damaged composite materials can be very costly and time‐consuming, motivating the development of self‐healing composites that recover their properties after a damage event. This work demonstrates the microcapsule‐based self‐healing of compression molded thermoplastic high impact polystyrene (HIPS) composites using a non‐toxic and environmentally friendly solvent, ethyl phenylacetate (EPA). EPA is incorporated within double‐walled polyurethane‐poly(urea‐formaldehyde) (PU/UF) microcapsules which are then integrated within the HIPS specimens. Flexure and fracture behavior, with and without microcapsules, is used to investigate the microcapsules' impact on composite physical properties and to determine the composite's self‐healing efficiency (up to 64%) after healing in response to fracture. Overall, this work demonstrates the inclusion of self‐healing properties in a commercially important polymer material with a non‐toxic and environmentally friendly solvent and motivates further development of thermoplastic self‐healing composites for industrial applications.

Cocoa bean turning as a method for redirecting the aroma compound profile in artisanal cocoa fermentation

Two artisanal fermentation processes for Criollo cocoa beans with different turning start times (24 h and 48 h) were studied. The aromatic profile of cocoa turned every 24 h (B1) displayed volatile compounds associated with fermented, bready, and fruity aromas. When cocoa beans were fermented with a different turning technique with a start time of 48 h (B2), they provided volatile compounds mainly associated with descriptors of floral, woody, sweet, fruity and chocolate aromas. The turning start time of 48 h stimulated a microbial profile dominated by yeast such as Hanseniaspora opuntiae, Pichia manshurica, and Meyerozyma carpophila, favoring the production of several key aroma markers associated with cocoa bean fermentation quality, such as phenylethyl acetate, 2-phenylacetaldehyde, 3-methylbutanal, 2-phenylethyl alcohol, 2,3-butanedione, 3-methylbutanoic acid, and 2-methylpropanoic acid, while an immediate turning start time (24 h) favored an aerobic environment that stimulated the rapid growth of Acetobacter pasteurianus, Bacillus subtilis and a higher biodiversity of lactic acid bacteria (LAB) (e.g., Lactobacillus plantarum and Pediococcus acidilactici), which increased the production of ethyl acetate and 3-hydroxy-2-butanone. Volatile compound generation and microbial populations were evaluated and analyzed by multivariate analysis (principal component analysis and partial least squares discriminant analysis) to find correlations and significant differences. This study shows that the method of turning Criollo cacao beans can lead to the formation of desirable aromatic compounds.

Unique volatile chemical profiles produced by indigenous and commercial strains of <i>Saccharomyces uvarum</i> and <i>Saccharomyces cerevisiae</i> during laboratory-scale Chardonnay fermentations

Each wine growing region hosts unique communities of indigenous yeast species, which may enter fermentation and contribute to the final flavour profile of wines. One of these species, Saccharomyces uvarum, is typically described as a cryotolerant yeast that produces relatively high levels of glycerol and rose-scented volatile compounds as compared with Saccharomyces cerevisiae, the main yeast in winemaking. Comparisons of fermentative and chemical properties between S. uvarum and S. cerevisiae at the species level are relatively common; however, a paucity of information has been collected on the potential variability present among S. uvarum strains. The objective of this study was to compare the fermentation kinetics and production of volatile compounds between indigenous and commercial Saccharomyces strains at different temperatures. We compared laboratory-scale fermentation of Chardonnay juice at 15 °C and 25 °C for 11 Saccharomyces yeast strains (six indigenous S. uvarum, one commercial S. uvarum, one indigenous S. cerevisiae and three commercial S. cerevisiae). Fermentation kinetics and the production of volatile compounds known to affect the organoleptic properties of wine were determined. The indigenous S. uvarum strains showed comparable kinetics to commercially sourced strains at both temperatures. Volatile compound production among the strains was more variable at 15 °C and resulted in unique chemical profiles at 15 °C as compared with 25 °C. Indigenous S. uvarum strains produced relatively high levels of 2-phenylethyl acetate and 2-phenylethanol, whereas these compounds were found at much lower levels in fermentations conducted by commercial strains of both S. cerevisiae and S. uvarum. Production of glycerol by indigenous S. uvarum strains did not differ from commercial strains in this study. Our findings demonstrate that indigenous strains of S. uvarum show functional variation among themselves. However, when compared with commercial S. cerevisiae and S. uvarum strains, they have comparable fermentation kinetics but unique volatile compound profiles, especially at low fermentation temperatures.

Coupling electronic nose with GC–MS improves flavor recognition and grade differentiation of Zhenjiang aromatic vinegar

AbstractIn this study, the flavor volatile profiles of five grades of Zhenjiang aromatic vinegar (ZAV) were compared using a gas chromatography‐mass spectrometer (GC–MS) and electronic nose (E‐nose). A total of 55 volatile compounds were identified, with 14 volatile compounds, including furfural, acetic acid, tetramethylpyrazine, phenethyl acetate, and phenylethyl alcohol, being identified as the key volatile compounds causing significant differences between different grades of ZAV samples. Principal component analysis (PCA) analysis of E‐nose data revealed that the W5S, W1W, W2W, W1S, and W2S sensors with high signal intensity to all ZAV samples correctly categorized the five grades of ZAV samples. The correlation analysis results suggested that the response signal intensities of W5S, W1W, and W2W had significant positive correlations with the abundances of acetic acid, isobutyric acid, ethyl phenylacetate, 3‐hydroxy‐2‐butanone, 2,3‐butanedione, 2‐acetylfuran, etc., adding to the evidence that W5S, W1W, and W2W sensors were sensitive to nitrogen oxides, sulfur compounds, pyrazines, and aromatic components. Based on the findings, it is possible to conclude that E‐nose, in conjunction with chemometric pattern recognition methods, can be used to differentiate between different grades of ZAV based on volatile compounds.Practical ApplicationsDifferent grades of Zhenjiang aromatic vinegar (ZAV) were distinguished by physical and chemical detection of total acid, nonvolatile acid, amino acid nitrogen and other indicators. In order to simplify the detection work, this study was to establish a rapid and feasible method for achieving ZAV grades differentiation according to their flavor volatile compounds. PCA of E‐nose data showed that the five grades of ZAV samples were well classified by the W5S, W1W, W2W, W1S, and W2S sensors. The correlation analysis results suggested that the response signal intensities of W5S, W1W, and W2W had significant positive correlations with the abundances of acetic acid, isobutyric acid, ethyl phenylacetate, 3‐hydroxy‐2‐butanone, etc., which adds to the proof that W5S, W1W, and W2W sensors were sensitive to nitrogen oxides, sulfur compounds, pyrazines and aromatic components. Therefore, E‐nose can be used as a rapid and nondestructive testing tool for quality measurements of ZAV.