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Despite being present in trace amounts, ethyl esters play a crucial role as flavour compounds in lager beer. In yeast, ethyl hexanoate, ethyl octanoate and ethyl decanoate, responsible for fruity and floral taste tones, are synthesized from the toxic medium chain acyl-CoA intermediates released by the fatty acid synthase complex during the fatty acid biosynthesis, as a protective mechanism. The aim of this study was to enhance the production of ethyl esters in the hybrid lager brewing yeast Saccharomyces pastorianus by improving the medium chain acyl-CoA precursor supply. Through CRISPR-Cas9-based genetic engineering, specific FAS1 and FAS2 genes harbouring mutations in domains of the fatty acid synthesis complex were overexpressed in a single and combinatorial approach. These mutations in the ScFAS genes led to specific overproduction of the respective ethyl esters: overexpression of ScFAS1 I306A and ScFAS2 G1250S significantly improved ethyl hexanoate production and ScFAS1 R1834K boosted the ethyl octanoate production. Combinations of ScFAS1 mutant genes with ScFAS2 G1250S greatly enhanced predictably the final ethyl ester concentrations in cultures grown on full malt wort, but also resulted in increased levels of free medium chain fatty acids causing alterations in flavour profiles. Finally, the elevated medium chain fatty acid pool was directed towards the ethyl esters by overexpressing the esterase ScEEB1. The genetically modified S. pastorianus strains were utilized in lager beer production, and the resulting beverage exhibited significantly altered flavour profiles, thereby greatly expanding the possibilities of the flavour palette of lager beers. • Ethyl esters play a crucial role as flavour compounds in lager beer. • Enhancing medium chain acyl-CoA improves production of ethyl esters in lager yeast. • Alleles ScFAS1 I306A and ScFAS2 G1250S improves ethyl hexanoate production in lager yeast. • Allele ScFAS1 R1834K boosted ethyl octanoate production in S. pastorianus. • Engineering of ethyl ester synthesis aids customizing aroma profiles lager yeast. [ABSTRACT FROM AUTHOR]

Aims Ethyl hexanoate, one of the key flavor compounds in strong-flavor Baijiu. To improve the content of ethyl hexanoate in strong-flavor Baijiu, a functional strain with high yield of ethyl hexanoate was screened and its ester-producing performance was studied. Methods and results Upon identification, the strain was classified as Candida sp. and designated as ZY002. Under optimal fermentation conditions, the content of ethyl hexanoate synthesized by ZY002 can be as high as 170.56 mg L−1. A fermentation test was carried out using the ZY002 strain bioaugmented Daqu to verify the role of the strain applied to Baijiu brewing. It was found that strain ZY002 could not only improve the moisture and alcohol contents of fermented grains but also diminish the presence of reducing sugar and crude starch. Furthermore, it notably amplified the abundance of flavor compounds. Conclusion In this study, Candida sp. ZY002 with a high yield of ethyl hexanoate provided high-quality strain resources for the actual industrial production of Baijiu. [ABSTRACT FROM AUTHOR]

The current work illustrates microwave-assisted synthesis of ethyl hexanoate without a solvent system using cationic resin (Amberlyst-15) as a catalyst. The effect of various parameters was evaluated, and a maximum equilibrium conversion of 84.2% was achieved in 50 min. The optimized parameters were 1:02 mole ratio of acid to alcohol, temperature 328 K, and 9% (w/w) catalyst loading. The impact of mole ratio and catalyst loading on the reaction rate was predicted by developing an empirical correlation. The activation energy was determined as 17.63 kJ/mol. The experimental data fitted well with Eley-Rideal mechanism, in which the surface reaction was a rate-limiting step. Thermodynamic parameters were evaluated, including standard enthalpy, Gibbs free energy, and reaction entropy. The energy consumption for microwave reaction was predicted as 15.357 × 105 kJ/kg. These results have been compared with that of conventional as well as ultrasound-assisted synthesis of ethyl hexanoate. This novel technique shows an enhancement in reaction rates and higher yields. [ABSTRACT FROM AUTHOR]

[Display omitted] • Application of cellar mud-sourced acid-producing bacteria and acid-tolerant esterifying yeast. • Co-culture solid-state fermentation of functional microbial to improve key flavor ethyl esters. • Ethyl hexanoate and ethyl butyrate were correlated with a cluster of interactions dominated by lactic acid bacteria. • Positive synergistic relationship between Clostridium tyrobutyricum and Saccharomyces cerevisiae. • Conversion of acids to esters by microorganisms in a high-acid fermentation system by stress reactions. Ethyl hexanoate and ethyl butyrate are indispensable flavor metabolites in strong-flavor Baijiu (SFB), but batch production instability in fermenting grains can reduce the quality of distilled Baijiu. Biofortification of the fermentation process by designing a targeted microbial collaboration pattern is an effective method to stabilize the quality of Baijiu. In this study, we explored the metabolism under co-culture liquid fermentation with Clostridium tyrobutyricum DB041 and Saccharomyces cerevisiae YS219 and investigated the effects of inoculation with two functional microorganisms on physicochemical factors, flavor metabolites, and microbial communities in solid-state simulated fermentation of SFB for the first time. The headspace solid-phase microextraction-gas chromatography-mass spectrometry results showed that ethyl butyrate and ethyl hexanoate significantly increased in fermented grain. High-throughput sequencing analysis showed that Pediococcus , Lactobacillus , Weissella , Clostridium _ sensu _ stricto _12, and Saccharomyces emerged as the dominant microorganisms at the end of fermentation. Co-occurrence analysis showed that ethyl hexanoate and ethyl butyrate were significantly correlated (|r| > 0.5, P < 0.05) with a cluster of interactions dominated by lactic acid bacteria (Pediococcus , Lactobacillus , Weissella , and Lactococcus), which was driven by the functional C. tyrobutyricum and S. cerevisiae. Mantel test showed that moisture and reducing sugars were the main physicochemical factor affecting microbial collaboration (|r| > 0.7, P < 0.05). Taken together, the collaborative microbial pattern of inoculation with C. tyrobutyricum and S. cerevisiae showed positive results in enhancing typical flavor metabolites and the synergistic effects of microorganisms in SFB. [ABSTRACT FROM AUTHOR]

Carob liqueur is an alcoholic drink (minimum 15% v/v of ethanol and 100 g/L of sugar) typical for the Mediterranean countries. In the current work, carob macerate produced by maceration of carob pods in hydroalcoholic base at different maceration conditions was characterized for the first time based on its aroma compounds/profile, physicochemical parameters, and chromatic characteristics. The results confirm the migration process of bioactive compounds, aroma compounds, and sugars flowing from the carob pod to the hydroalcoholic base. Changes in ethanol concentration modify the physical properties of the solvent and influence the phenolic and aroma compounds extraction, color, and acidity of the obtained samples. The higher content of phenolic compounds was determinate in the samples obtained in the darkness. The amounts of phenols were in the range of some red fruit liqueurs or walnut liqueurs, and sugars (mostly sucrose) ranging between 96 and 107 g/L. Twenty‐six (out of total 94) aroma compounds were detected in all samples, of which 17 esters, 3 alcohols, 4 ketones, and 2 acids. Low molecular weight ethyl esters, ethyl hexanoate, ethyl 2‐methyl propanoate, ethyl octanoate, ethyl benzoate, ethyl butanoate, and ethyl cinnamate, were the most abundant. Carob pod maceration in 50% v/v hydroalcoholic base (1:5 solid to liquid ratio) in darkness at room temperature during 8 weeks can be recommended as optimal maceration conditions for production of the aromatic carob macerate with functional properties. [ABSTRACT FROM AUTHOR]

BACKGROUND: Strawberries are perishable fruits that decay quickly after harvest, but are valued for their distinctive taste and aroma. Melatonin is involved in plant resistance against stress, plant senescence and fruit ripening, and was shown to delay post-harvest spoilage of strawberries. OBJECTIVE: The effects of melatonin postharvest treatment on shelf-life and volatile organic compound profile were assessed in strawberry fruits cv "Luca". METHODS: Strawberry fruit were treated with 100 μM melatonin and stored at 4°C for 12 days to assess whether melatonin treatment could delay spoilage without adversely affecting aroma. RESULTS: Melatonin treatment delayed fruit deterioration by reducing weight loss and incidence of decay as well as maintaining total soluble solids, titratable acidity, anthocyanin, and taste. Melatonin treatment also significantly reduced CO2 production compared to control fruits. The relative abundance of the majority of volatile organic compounds (VOCs) was not affected, however abundance of two VOCs that are important components of strawberry aroma were affected by melatonin treatment. CONCLUSIONS: Post-harvest treatment of strawberries with 100 μM melatonin improved strawberry quality and conserved bioactive compounds after 12 d of storage. However, components of the aroma profile were altered in a way which may affect consumer perception of quality. [ABSTRACT FROM AUTHOR]

This study was conducted to extract scarce natural liquor flavorings desired by many liquor factories from yellow water. Five straight-chain saturated fatty acids were firstly extracted from 15 fractions of yeHow water, forming 1 fraction of the ethanol solution composed of the mixture of the five straight-chain saturated fatty acids. Then, 100 fractions of the ethanol solution could produce 94. 857 6 fractions of esterification liquid through catalytic esterification at 80 m. The esterification liquid contains five esters: ethyl acetate, ethyl propionate, ethyl butyrate, ethyl valerate and ethyl caproate, with contents of 17. 68V, 2. 58V, 6. 32%, 0.06V and 19.40V, respectively. The esterification liquid prepared from 1 fraction of yeHow water could blend 10. 54 fractions of white liquor into top-grade Luzhou-flavor liquor after esterification. It indicates that yeHow water has very good recycling and utilization value. [ABSTRACT FROM AUTHOR]

Yeast cells ( Saccharomyces cerevisiae ), from which β-glucans have been partially extracted, were used to encapsulate flavor inside the lipid bilayer membrane as natural encapsulant. The focus of this study was to investigate the release and stability of flavors ( d -limonene and ethyl hexanoate) encapsulated in yeast cells and maltodextrin (MD) (DE = 19) by spray drying. The release behavior of encapsulated flavors from yeast cells was measured at 40, 60, 80, and 105 °C with different moisture content (0, 50, 100, and 200% of powder). Water affected flavor release from the yeast cells. The release rate constants were correlated using Gaussian distribution of the activation energy of the release rate constants. The release of d -limonene from the spray-dried MD powder showed a different trend than that of yeast cells at various temperatures. The activation energies of the release rate constant for ethyl hexanoate and d -limonene from yeast were 55 and 49 kJ/mol, respectively, under a wet condition. The formation rates of limonene oxide and carvone were slower in yeast than that of MD powder at 30 °C after 2 months. [ABSTRACT FROM AUTHOR]

Flavor encapsulation was investigated by spray drying with dried Saccharomyces cerevisiae cells. The yeast cells, Saccharomyces cerevisiae , which were by-products in the production of β-glucan, were used in the encapsulation of d -limonene and ethyl hexanoate. Effects of incubation time, temperature, and spray drying conditions on the encapsulated flavor content after spray drying were investigated. The encapsulation rate constant was 0.69 h −1 for d- limonene and ethyl hexanoate. High contents of both flavors were obtained at an incubation temperature of 40 °C for 4 h and an inlet air temperature of 200 °C for spray drying. Inlet air temperature did not significantly affect encapsulation of flavor content for ethyl hexanoate. Flavor content obtained was 37 wt% for d -limonene and 49 wt% for ethyl hexanoate at an inlet air temperature 200 °C. Thus, yeast could be used as a successful flavor-encapsulant by spray drying. [ABSTRACT FROM AUTHOR]

This study aimed at isolating and culturing Bacilli from the omagari, pit mud, and fermented grains used in Luzhou-flavor liquor in an effort to produce better flavor and quality. After an enrichment culture of Bacillus in the omagari, pit mud, and fermented grains of Luzhou-flavor liquor, 52 total strains were obtained. Based on the standard of producing high-yield ethyl hexanoate and low-yield propanol, one strain named YB-1 was screened out. It was shown that YB-1 produced ethyl hexanoate at 214.7 mg/100 mL and propanol at 0 mg/100 mL. Based on strain morphology, and physiological and biochemical characteristics, YB-1 was identified as Bacillus. According to DNA sequencing and the constructed phylogenetic tree, YB-1 and Bacillus cereus strain CCM 2010 clustered into a branch and were each other's closest relatives. Thus, YB-1 was identified as Bacillus cereus. Through this research, it is expected that the application of Bacillus cereus strain YB-1 to the traditional brewing process of Luzhou-flavor liquor could improve the flavor and quality, and enrich microbial resources for Luzhou-flavor liquor fermentation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Grape pomace was exploited for the obtainment of highly concentrated hexanoic acid. • Hexanoic acid was reacted with ethanol by using AlCl 3 ·6H 2 O as a catalyst. • Ethyl hexanoate was obtained in high yields (>90 %). • AlCl 3 ·6H 2 O was recoverable and reusable, with no loss in its catalytic effectiveness. • AlCl 3 ·6H 2 O increased reaction yield and it promoted a process intensification. A novel viable route for obtaining ethyl hexanoate-rich streams from grape pomace, an agro by-product generated from the winery industry, was investigated. Highly concentrated hexanoic acid (87 wt%) was efficiently produced through the chain elongation fermentation of red and white grape pomace, easily separated, recovered and reacted with ethanol by using AlCl 3 ·6H 2 O as a catalyst. Under the optimised mild reactive conditions (molar ratio acid:ethanol:catalyst of 1:2:0.1, 5 h, 348 K), a high conversion equal to 93.5 % was achieved in a single step. AlCl 3 ·6H 2 O was very effective in catalysis, playing an additional key role in the separation of products, shifting the equilibrium of the reaction and making products' recovery easier. After the reaction cycle, the catalyst was easily recoverable and reusable without losing effectiveness. According to this simple layout of processes, including the anaerobic digestion of the residual part of grape pomace, a specific production cost of 0.935 €·kg−1 was calculated related to the final products. This proposed approach could represent a promising green and sustainable route to produce ethyl esters of volatile fatty acids from agro by-products. [ABSTRACT FROM AUTHOR]

Ethyl hexanoate is one of the most important esters in the strong aromatic Baijiu. In this study, Saccharomyces cerevisiae AY14α was engineered to improve the production of ethyl hexanoate. The CRISPR/Cas9 system was constructed for strain AY14α, and the gene expression intensity was compared at the different integration sites. The hexanoyl-CoA synthesis pathway and alcohol acyltransferase gene were introduced into AY14α, and the recombinant strain Rb-HCSTB accumulated 8.76 ± 1.53 mg/L of ethyl hexanoate. The genes of the hexanoyl-CoA synthesis pathway from different microorganisms and the genes encoding alcohol acyltransferase from different fruits were introduced into AY14α to study their functions. The synthetic pathway of ethyl hexanoate was optimized, and the production of ethyl hexanoate reached 42.35 ± 1.75 mg/L by using the recombinant strain Ck-HCVB-2CbeTer. This work provided a reference for the construction of microorganisms producing ethyl hexanoate and the improvement of ethyl hexanoate production in Baijiu fermentation. • AY14α was engineered to produce ethyl hexanoate for improvement of Baijiu quality. • Some foreign genes are more helpful for ethyl hexanoate synthesis in AY14α. • Ethyl hexanoate production increases to 42.35 mg/L in AY14α after the optimization. [ABSTRACT FROM AUTHOR]

Abstract: The composition of the essential oils of pequi fruits gathered from the Brazilian Cerrado ecosystem in the states of Maranhão (MA), Minas Gerais (MG) and Tocantins (TO) was investigated. The oils were obtained by steam distillation, and each component was speciated using GC-MS. The oil content varied from 0.13% to 1.15%. Interestingly, the major substance found within samples from two of the states was ethyl hexanoate (MA, MG), whereas isopropyl hexanoate and isopentyl-2-methylbutanoate were specific for the samples from TO. Both principal components analysis (PCA) and hierarchical cluster analysis (HCA) were used for exploratory analysis of the oils, and, consequently, the pequi fruits were classified according to their place of origin. The PCA showed that 51.5% of the variance accumulated in the PC1 and PC3, and the group formation obtained using HCA confirmed that the oil composition is influenced by geographic and/or plant genetic factors. Such analyses could assist in the selection of more flavoursome and healthy variants of pequi. [Copyright &y& Elsevier]

In this study, the effects of texture modification and aroma-induced sweetness enhancement were systematically investigated in apple-flavored semi-solid Na-caseinate gels. Gels containing apple juice as a basic flavor were developed differing in stiffness, brittleness and serum release (texture modification), aroma, and sugar concentration (flavor modification). In a full factorial design (2 × 2 × 2), eight samples were evaluated by a sensory panel on ten attributes (five texture, five flavor). Sweetness was enhanced significantly by modification of texture, aroma, and sugar concentration. Texture modification was found to be by far the greatest contributor to overall sweetness. In comparison to texture modifications, aroma modification and changes of sugar concentration resulted only in small sweetness enhancement. When texture and aroma modifications are combined, a small additive effect of aroma modification on sweetness enhancement was found in addition to the sweetness enhancement caused by texture modification. This suggests that the relationship between texture (modification) and flavor (modification) and sweetness is additive in a nonlinear manner. It can be concluded that texture modification is a valid tool to enhance taste intensity. Hence, texture modification can compensate for a loss of sweet taste intensity induced by sugar reduction, while aroma-induced sweetness enhancement can contribute to further taste enhancement in order to develop healthier products. [ABSTRACT FROM AUTHOR]

The volatile composition of different parts (whole fruit, peel and flesh) of a rare wild red apple named "Mela Rossa Val Metauro" was established by SPME (Solid Phase Micro-Extraction) sampling, followed by GC-MS analysis. The most prominent constituent in all the three parts was the sesquiterpene (E,E)-α-farnesene. The presence of the ester ethyl hexanoate particularly in the flesh (39.8%) gives a special exotic flavor to the fruit. [ABSTRACT FROM AUTHOR]

The aim of the current study is to predict the release kinetics of organic molecules entrapped in sol-gel-made silica particles using both pulsed field gradient-nuclear magnetic resonance (PFG-NMR) techniques and model calculations to describe restricted diffusion. The macroscopic release profile of aroma molecules from sol-gel-made particles is measured directly by UV-VIS spectroscopy, while the release kinetics are calculated by the Crank equation. The microscopic restricted pore diffusion coefficient of the aroma molecules in the Crank equation is obtained in situ by pulsed field gradient (PFG) magic angle spinning (MAS) nuclear magnetic resonance (NMR). Furthermore, restricted pore diffusion coefficients obtained by model calculations are in agreement with those measured by PFG-MAS-NMR, indicating the potential of the latter for characterization and screening of encapsulation formulations. Measured and calculated release profiles agree within experimental error. [Copyright &y& Elsevier]

Abstract: The aroma volatiles of Caryocar brasiliense, the “pequi” fruit, were analyzed by GC and GC–MS. It is rich on vitamins, lipids and proteins and an edible fruit after cooking. The “pequi” flavor has been used to aromatize many foods eaten up in the Central West and South Eastern of Brazil. The ethyl esters prevailed in the aroma concentrate of “pequi” followed by other analogous esters, saturated fatty acids and long chain hydrocarbons. The major component was ethyl hexanoate (52.9%) followed of minor amounts of ethyl octanoate (4.6%), tetrahydrofurfurylalcohol (4.3%), ethyl butanoate (4.1%), butyl palmitate (3.7%), isobutyl stearate (2.6%) and 3-methylvaleric acid (2.6%). The fatty acids and their derivatives varied from C-8 (caprylic acid and ethyl octanoate) to C-18 (stearyl acetate and isobutyl stearate). The existing homologous series of hydrocarbons ranged from C-11 (undecane) to C-26 (hexacosane). [Copyright &y& Elsevier]

The thermophysical properties of biodiesel surrogates are of great importance for the development of the new and clean fuel substitutes or additives. Experimental investigation and molecular dynamic simulation of the related thermophysical properties such as the liquid density, kinematic viscosity and surface tension over a sufficient wide temperature range will facilitate the corresponding researches of selecting the proper fuel surrogates and designing the spray system of the internal combustion engine. Therefore, the present study investigated liquid surface tension and kinematic viscosity of the proposed physical biodiesel surrogates of n-hexadecane with ethyl hexanoate and ethyl heptanoate by the surface light scattering method at three mole fractions (0.25, 0.50 and 0.75) over the temperature range from (353.15 to 433.15) K. Additionally, the liquid density was also determined by a U-tube densimeter in the temperature range between (293.15 and 433.15) K. Meanwhile, three force fields including OPLS-AA, GROMOS and AMBER were selected and validated with n-hexadecane and ethyl heptanoate in a wide temperature range and the GROMOS force field was demonstrated to be the best one for the description of the three thermophysical properties of the two fluids. A further molecular dynamic simulation with GROMOS force field was applied to the proposed binary surrogates of n-hexadecane with ethyl hexanoate and ethyl heptanoate, and the results for the three properties agreed well with their experimental values over the entire temperature range. • The binary mixtures of two FAEEs and n-dodecane might be used as model fuels. • Thermophysical properties of the selected systems were investigated. • Surface light scattering method was used for the determination of surface properties. • Molecular dynamic simulation method was used for the simulation of thermophysical properties. • Correlations were proposed for the investigated thermophysical properties. [ABSTRACT FROM AUTHOR]

• Ethyl hexanoate injection increase brown adipose tissue sympathetic nerve activity. • Ethyl hexanoate injection increase white adipose tissue sympathetic nerve activity. • Ethyl hexanoate injection enhances thermogenesis and lipolysis. • Autonomic changes due to Ethyl Hexanoate a realize via afferent vagal nerve. The autonomic nervous system (ANS) is implicated in maintaining homeostasis of the internal environment in mammals. Therefore, changes occurring in the ANS can cause alterations of physiological phenomena. Ethyl hexanoate (EH) is known as the aroma component of apples. To study the action of ethyl hexanoate on physiological phenomena, we examined the effect of an intragastric (IG) injection of 1 mL/kg body weight of 0.1 ppm EH solution on sympathetic nerve activity innervating the brown adipose tissue (BAT) and white adipose tissue (WAT) in anesthetized rats. Consequently, IG administration of EH increased activity of the sympathetic nerves innervating both the BAT and WAT. In addition, the effects of the IG injection on body temperature above the interscapular BAT and plasma free fatty acid (FFA) concentration were also examined in conscious rats. In this attempt IG injection of EH elevated both the body temperature and plasma FFA levels. Furthermore, subdiaphragmatic vagotomy eliminated the effects of EH on sympathetic nerves innervating BAT and WAT. These findings suggest that EH causes excitations of sympathetic nerves innervating BAT and WAT, and enhances thermogenesis and lipolysis via the afferent vagus nerve. Thus, these present findings also suggest the possibility that EH might have anti-obesity effects. [ABSTRACT FROM AUTHOR]

• Vapor pressures of two key apple odorants were measured. • Measurements were made over the temperature range of (340 to 441) K. • The parameters of Antoine and Wagner type equations were estimated. • The relative deviations from the three vapor pressure equations were <0.9%. • Vaporization enthalpies were estimated using the Clapeyron equation. Vapour pressure complementary data for two key apple aroma esters, ethyl butyrate and ethyl hexanoate, two compounds with high relevance to the food industry, were measure with a dynamic recirculation apparatus. For pressures from (15 to 105) kPa the temperatures experimentally assessed were from (340.1 to 395.2) K for ethyl butyrate, and from (378.4 to 440.9) K for ethyl hexanoate. Results of the vapour pressures were correlated using Antoine's, extended Antoine's and Wagner's equations. Relative root mean square deviations were lower than 0.38% and 0.94% for ethyl butyrate and ethyl hexanoate, respectively. Experimental data of dibutoxymethane showed reasonable consistency with the information available in the literature. The vaporisation enthalpies were evaluated using the Clapeyron equation, together with the Virial equation of state to estimate the vapour compressibility factor, as well a correlation for saturated liquid molar volume. The results for both esters were comparable with data from the literature. [ABSTRACT FROM AUTHOR]