Ester Aroma Research Articles

Evaluation of the perceptual interaction among ester aroma compounds in cherry wines by GC–MS, GC–O, odor threshold and sensory analysis: An insight at the molecular level

The ester aroma profiles of five Chinese cherry wines and the perceptual interaction among esters were investigated in this study. 24 esters were identified by Gas chromatography-olfactometry (GC–O) and Gas Chromatography-Mass Spectrometer (GC–MS). According to addition/omission analysis, seven volatile compounds among them were selected and studied using sensory profiling and multivariate statistic methods such as Principal Component Analysis (PCA). In sensory analysis, a significant reduction of olfactory threshold for total aromatic reconstitution was induced by the addition among each of them in Feller’s additive model, which demonstrated their synergistic effects. The σ/τ plot showed that most of them were followed by a partial addition behavior. Furthermore, PCA indicated that the addition among each of them had a significant effect on fruity, floral, sweet and fermentation aroma intensity. Specifically, ethyl decanoate and methyl salicylate at sub-threshold concentrations were also likely to contribute to overall aroma. The results of perceptual interaction were mainly influenced by chemical structure and molecular polarity.

Effect of mixed yeast starter on volatile flavor compounds in Chinese rice wine during different brewing stages

The volatile compounds of Chinese rice wine fermented by Saccharomyces cerevisiae FC 15 and S. cerevisiae BR 30 and their combination (MIX) were investigated. The results showed that the wines fermented with different starters differed mainly in the numbers of alcohols and esters. Furthermore, the amounts of volatile compounds among three starters were also obviously different. After clarification, the loss of esters was greater than that of alcohols and aldehydes, whereas after sterilization, the loss of aldehydes was the greatest. PCA showed diethyl succinate to be the key flavor component. Moreover, short-chain fatty acid ethyl esters were main flavor substances during fermentation, whereas long-chain fatty acid ethyl esters were typical compounds after clarification and sterilization. Analysis of the ratio of higher alcohols to esters showed that BR 30 wine presented a stronger ester aroma than MIX wine, whereas FC 15 wine exhibited an outstanding alcohol flavor. Sensory evaluation indicated that FC 15 wine was intense in alcohol-aroma, whereas BR 30 wine exhibited high levels of cereal-aroma. Furthermore, both MIX and BR 30 wine were highly assessed in continuation and full body mouth-feel. It means that flavor characteristic of Chinese rice wine could be adjust by combination of yeast starters.

Olfactory Impact of Higher Alcohols on Red Wine Fruity Ester Aroma Expression in Model Solution

This study focused on the impact of five higher alcohols on the perception of fruity aroma in red wines. Various aromatic reconstitutions were prepared, consisting of 13 ethyl esters and acetates and 5 higher alcohols, all at the average concentrations found in red wine. These aromatic reconstitutions were prepared in several matrices. Sensory analysis revealed the interesting behavior of certain compounds among the five higher alcohols following their individual addition or omission. The "olfactory threshold" of the fruity pool was evaluated in several matrices: dilute alcohol solution, dilute alcohol solution containing 3-methylbutan-1-ol or butan-1-ol individually, and dilute alcohol solution containing the mixture of five higher alcohols, blended together at various concentrations. The presence of 3-methylbutan-1-ol or butan-1-ol alone led to a significant decrease in the "olfactory threshold" of the fruity reconstitution, whereas the mixture of alcohols raised the olfactory threshold. Sensory profiles highlighted changes in the perception of fruity nuances in the presence of the mixture of higher alcohols, with specific perceptive interactions, including a relevant masking effect on fresh- and jammy-fruit notes of the fruity mixture in both dilute alcohol solution and dearomatized red wine matrices. When either 3-methylbutan-1-ol or butan-1-ol was added to the fruity reconstitution in dilute alcohol solution, an enhancement of butyric notes was reported with 3-methylbutan-1-ol and fresh- and jammy-fruit with butan-1-ol. This study, the first to focus on the impact of higher alcohols on fruity aromatic expression, revealed that these compounds participate, both quantitatively and qualitatively, in masking fruity aroma perception in a model fruity wine mixture.

Enhanced acetate ester production of Chinese liquor yeast by overexpressing ATF1 through precise and seamless insertion of PGK1 promoter.

As the most important group in the flavor profiles of Chinese liquor, ester aroma chemicals are responsible for the highly desired fruity odors. Alcohol acetyltransferase (AATase), which is mainly encoded by ATF1, is one of the most important enzymes for acetate ester synthesis in Saccharomyces cerevisiae. In this study, we overexpressed ATF1 in Chinese liquor yeast through precise and seamless insertion of PGK1 promoter (PGK1p) via a novel fusion PCR-mediated strategy. After two-step integration, PGK1p was embedded in the 5'-terminal of ATF1 exactly without introduction of any extraneous DNA sequence. In the liquid fermentation of corn hydrolysate, both mRNA level and AATase activity of ATF1 in mutant were pronounced higher than the parental strain. Meanwhile, productivity of ethyl acetate increased from 25.04 to 78.76mg/l. The self-cloning strain without any heterologous sequences residual in its genome would contribute to further commercialization of favorable organoleptic characteristics in Chinese liquor.

Effects of Salt Stress on Growth, Ion Concentration, and Quality of Pineapple Fruits

This work was aimed to investigate the growth, ion contents, quality, and aroma components of pineapple fruits as affected by salinity stress. Pot experiments with four levels of salinity [0, 0.25%, 0.50%, and 0.75% sodium chloride (NaCl)] and eight replications were conducted in a plastic shed. The results suggested that the transverse diameter and longitudinal diameter as well as weight per fruit of pineapple fruits declined with increasing salinity. Salt stress caused the increasing of sodium (Na+). Salt stress resulted in the significant decreasing of potassium (K+)/Na+ and calcium (Ca2+)/Na+ with decreasing contents of K+ and Ca2+. Salt stress slightly affected the chemical quality of pineapple fruits. The firmness of fruit was significantly decreased. The total relative content of ester aroma components was increased by lower salt stresses at 0.25% and 0.50% and was decreased by high salt stress at 0.75%. The characteristic aroma component was not identified in the salt-stressed fruits.

Effect of Pasteurization on the Protein Composition and Oxidative Stability of Beer during Storage

The impacts of pasteurization of a lager beer on protein composition and the oxidative stability were studied during storage at 22 °C for 426 days in the dark. Pasteurization clearly improved the oxidative stability of beer determined by ESR spectroscopy, whereas it had a minor negative effect on the volatile profile by increasing volatile compounds that is generally associated with heat treatment and a loss of fruity ester aroma. A faster rate of radical formation in unpasteurized beer was consistent with a faster consumption of sulfite. Beer proteins in the unpasteurized beer were more degraded, most likely due to proteolytic enzyme activity of yeast remnants and more precipitation of proteins was also observed. The differences in soluble protein content and composition are suggested to result in differences in the contents of prooxidative metals as a consequence of the proteins ability to bind metals. This also contributes to the differences in oxidative stabilities of the beers.

Influences of organic manure addition on the maturity and quality of pineapple fruits ripened in winter

Abstract A field experiment was conducted to investigate the influence of the addition of or-ganic manure on the maturity stage and quality of pineapple fruits ripened in winter. Fertilization was performed with 200 mL peanut-press pulp liquid fertilizer + 20 g compound fertilizer per plant (T1) or 100 mL peanut press pulp liquid fertilizer + 20 g compound fertilizer per plant (T2). Fertilization with 20 g compound fertilizer per plant (T0) was used as the control. The results indicated that organic fertilizer addition promoted maturity. The weight per fruit was increased, and the contents of TSS and total sugars were enhanced, whereas the titratable acid contents were decreased. A sensory evaluation indicated that, after the addition of organic manure, the pineapple fruits were sweeter and more fragrant. More types of ester aroma com-ponents having a higher total relative content were identified in T1, and more types of alkenes having a higher total relative content were identified in T2. The relative contents of propanoic acid, 3-(methylthio)-, and methyl ester were increased by or-ganic manure treatments, with the highest being noted in T1 (5.79%), followed by T2 (5.59%), and the lowest was documented in T0 (4.36%).Keywords: pineapple, fruits ripened in winter, organic manure, maturity stage, quality

Gene cloning of phenolic acid decarboxylase from Bacillus subtilis and expression in top-fermenting yeast strain

Phenolic acid decarboxylase ( PADC ) gene, encoding phenolic acid decarboxylase, was cloned from Bacillus subtilis and ligated with a shuttle vector YEp352 to generate a novel plasmid YPADC. By analysis of sequencing and the restriction endonuclease digestion, the validity of construction was proved. Subsequently, the new vector was successfully transformed into wild-type top-fermenting yeast strain W303-1A; the mutant yeast strain W303+padc was obtained, which was tested on the laboratoryscale mashing and fermentation experiments. At the end of fermentation, the results showed an obvious increase of 4-vinylguaiacol content in top-fermented beers brewed with mutant yeasts. The final 4-vinylguaiacol concentration obtained with wild-type and mutant yeasts was 1.20 and 1.70mg/l, respectively. Additionally, the level of esters produced by the mutant strain was higher than that of the wild-type; there were therefore a marked clove-like and ester aroma in top-fermented beers brewed with the former. However, no evident differences were found in brewing characteristic between wild-type and mutant strains, especially the ability of utilizing fermentable sugar and reducing diacetyl. Taken together, these approaches indicated the possibility of cloning PADC gene and enhancing the concentration of 4-vinylguaiacol in top-fermented beers.size. Keywords : Clone, phenolic acid decarboxylase, top-fermenting yeast, 4-vinylguaiacol African Journal of Biotechnology Vol. 9(33), pp. 5284-5291, 16 August, 2010

An Esterification Kinetics Experiment That Relies on the Sense of Smell

This experiment involves an esterification synthesis to study reaction kinetics where students explore these topics utilizing the sense of smell rather than the traditional approach of using spectroscopic methods. Students study the effects of various factors including the concentration of the carboxylic acid and the amounts of the catalyst or alcohols added. The kinetics in relation to the molecular structure is studied by changing the chain lengths and branching of alcohols or the carboxylic acids and inferring the effects on rates of the reaction from the rates of ester detection. Since many esters have naturally occurring aromas that are pleasant and easily recognized, this experiment studies esterification kinetics using the sense of smell to detect the emergence of the ester aroma formed during the reaction. Feedback from students strongly suggests their interest in the experiment as they discovered that their sense of smell could be used as an analytical tool.

Biochemical and Catalytic Properties of Three Recombinant Alcohol Acyltransferases of Melon. Sulfur-Containing Ester Formation, Regulatory Role of CoA-SH in Activity, and Sequence Elements Conferring Substrate Preference

Alcohol acyltransferases (AAT) play a key role in the biosynthesis of ester aroma volatiles in fruit. Three ripening-specific recombinant AATs of cantaloupe Charentais melon fruit (Cm-AAT1, Cm-AAT3, and Cm-AAT4) are capable of synthesizing thioether esters with Cm-AAT1 being by far the most active. All proteins, as well as AAT(s) extracted from melon fruit, are active as tetramers of around 200 kDa. Kinetic analysis demonstrated that CoA-SH, a product of the reaction, is an activator at low concentrations and an inhibitor at higher concentrations. This was confirmed by the addition of phosphotransacetylase at various concentrations, capable of modulating the level of CoA-SH in the reaction medium. Site-directed mutagenesis of some amino acids that were specific to the Cm-AAT sequences into amino acids that were consensus to other characterized AATs greatly affected the selectivity of the original protein and the number of esters produced.

Yeast ADHI Disruption: A Way to Promote Carbonyl Compounds Reduction in Alcohol-Free Beer Production

Alcohol-free beers are usually characterized by worty off-flavors and the lack of the pleasant fruity or ester aroma found in regular beers. Enhancing yeast reduction of 3-methylthiopropionaldehyde, 3-methylbutanal, and 2-methylbutanal appears to be a good means of improving the organoleptic quality of alcohol-free beers. Upon screening of various Saccharomyces cerevisiae yeasts for in vitro reductase activity, a haploid adh0 strain emerged as the most efficient yeast for nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH)-dependent Strecker aldehyde reduction. Tetrad analysis of diploids (adh0 × 15D wild-type) demonstrated the predominant role of adh1 mutation to enhance aldehyde reductase. Consequent to such alcohol dehydrogenase gene disruption, acetaldehyde accumulates, although partly oxidized into acetic acid by the NADP cofactor. We propose that regeneration of this cofactor in adh1 strains can be improved by promoting NADPH-dependent aldehyde reductase activity.