Evolution of volatile byproducts during wine fermentations using immobilized cells on grape skins

A biocatalyst was prepared by immobilization of Saccharomyces cerevisiae cells on grape skins. Repeated batch fermentations were conducted using this biocatalyst as well as free cells, at 25, 20, 15, and 10 degrees C. Solid phase microextraction (SPME) was used in monitoring the evolution of volatile byproducts. The effect of immobilization and temperature on evolution patterns of volatiles was obvious. The major part of esters was formed after consumption of 40-50% of the sugars. Similar processes were observed for amyl alcohols and 2-phenylethanol, whereas 1-propanol and 2-methyl-1-propanol were formed during the whole alcoholic fermentation period at an almost constant formation rate. Acetaldehyde and acetoin were synthesized in the early stages of fermentation. Afterward, their amount decreased. In most cases, immobilized cells exhibited higher formation rates of volatiles than free cells. The final concentration of esters was higher in wines produced by immobilized biocatalyst. Their amount increased with temperature decrease. The opposite was observed for higher alcohols.     

Monitoring ester formation in grape juice fermentations using solid phase microextraction coupled with gas chromatography-mass spectrometry

Volatile esters contribute important floral and fruity sensory properties to wine. Numerous factors influence the biosynthesis and hydrolysis of esters throughout yeast fermentation; however, methods to monitor the dynamic changes in ester production that occur during winemaking processes are limited. In this study, we showed that solid phase microextraction (SPME), a rapid, solventless sampling procedure, combined with GC/MS analysis is a useful method for the nearly continuous analysis of volatile compounds such as esters that are produced during fermentation. Accuracy, precision, and limits of quantification were comparable to those of other sample preparation methods such as liquid-liquid extraction. Using GC/MS-SPME to monitor fatty acid ethyl esters and acetate esters, we obtained detailed information on the production patterns of ester formation during fermentation. This method now enables the monitoring of volatiles during fermentation and can provide greater insight into yeast metabolism and flavor formation.     

Extremely low temperature fermentations of grape must by potato-supported yeast, strain AXAZ-1. A contribution is performed for catalysis of alcoholic fermentation

This investigation announces the use of potato pieces as a suitable support for cell immobilization resulting in extremely low temperature wine making. The results showed an increase of the total esters by immobilized cells and reduction of higher alcohols. Likewise, percentages of total esters on total volatiles were increased by the drop in temperature, while percentages of higher alcohols were reduced in wines. Kinetics experiments at different temperatures allowed the calculation of activation energy (Ea) and showed reduction in the case of immobilized cells as compared with free cells. These results may lead to the conclusion that the increased productivities that are obtained by immobilized cells, can be attributed to the catalytic activity by the support to enzymes, which are involved in the process. Biocatalysts were prepared by immobilization of Saccharomyces cerevisiae, strain AXAZ-1, on whole potatoes and potato pieces, and their efficiency for alcoholic repeated batch fermentations of glucose and grape must in the range 2-30 degrees C was examined. To study the operational stability of biocatalyst, 35 repeated batch fermentations of grape must were performed without any significant reduction of the fermentation activity. Wines were analyzed for volatile byproducts determination by GC and GC-MS.     

Red wine making by immobilized cells and influence on volatile composition

Red wine making using yeast cells immobilized in two types of raisin berries, at various temperatures (6-30 degrees C), was studied. A modification of the batch bioreactor was used to separate the grape skins used for color extraction from the biocatalyst and the fermenting grape must. The evaluation of the immobilized biocatalysts was made on terms of productivity and organoleptic quality, including color intensity and formation of volatiles. The immobilized cells were found capable of low-temperature wine making, producing red wines containing more than 11% v/v alcohol in 8 days at 6 degrees C. The quality of wines was examined by gas chromatography (GC) and GC-MS analysis and sensory evaluation. Higher alcohol concentrations were decreased, and ethyl acetate concentrations increased by the drop of temperature. Many esters, alcohols, carbonyls, and miscellaneous compounds were identified in wines produced by immobilized cells, revealing no significant qualitative differences as compared to wines produced by free cells. The sensory evaluation showed that the best red wine was produced at 6 degrees C.     

Volatile compounds of wines produced by cells immobilized on grape skins

A biocatalyst was prepared by immobilization of Saccharomyces cerevisiae cells on grape skins. Repeated batch fermentations were conducted using the immobilized biocatalyst as well as the free yeast cells at 25, 20, 15, and 10 degrees C. The major volatile byproducts were determined by GC, whereas the minor volatile constituents were extracted in dichloromethane and analyzed by HRGC-MS. The qualitative profiles of the wines produced were similar in every case. Immobilized cells gave wines with higher contents of ethyl and acetate esters that increased with temperature decreases from 25 to 15 degrees C. The amount of volatile alcohols was more pronounced in wines produced by free cells and decreased dramatically at low fermentation temperatures (10 degrees C).     

Changes in the concentration of yeast-derived volatile compounds of red wine during malolactic fermentation with four commercial starter cultures of Oenococcus oeni

The effects of malolactic fermentation (MLF) on the concentration of volatile compounds released by yeasts during the production of red wine were investigated by inoculation with four commercial starters of Oenococcus oeni. Volatile compounds in wine at the end of MLF were extracted, analyzed by GC-MS and GC, and compared with those extracted form a noninoculated reference sample. Several esters known to play a role in the aroma profile of red wine, such as C4-C8 ethyl fatty acid esters and 3-methylbutyl acetate, were found to increase with MLF, and their final concentration was dependent on the bacterial starter employed for the induction of MLF. The overall increase of ethyl fatty acid esters was generally larger than the one observed for acetate esters. Ethyl lactate, 3-hydroxybutanoate, 2-phenylethanol, methionol, and gamma-butyrolactone were also increased by bacterial metabolism. The impact of MLF on other volatiles or red wine, including several higher alcohols, fatty acids, and nitrogen compounds, was generally negligible.     

Formation of volatile branched chain esters in bananas (Musa sapientum L.)

Substrates controlling the formation of branched chain volatile esters in ripening bananas were investigated by the application of alcohol and amino acid precursors to whole fruit and tissue samples. The resulting changes in the profile of the volatile esters were determined using SPME and GC. These changes revealed the selectivity characteristics of the esterification enzyme AAT, the availability of acyl CoA's for ester formation, and the role of substrate supply on volatile production. The results obtained suggest that substrate supply is a major determinant of the quantitative and qualitative composition of the resulting aroma profile.     

Screening of tropical fruit volatile compounds using solid-phase microextraction (SPME) fibers and internally cooled SPME fiber

In this study, the optimization and comparison of an internally cooled fiber [cold fiber with polydimethylsiloxane (PDMS) loading] and several commercial solid-phase microextraction (SPME) fibers for the extraction of volatile compounds from tropical fruits were performed. Automated headspace solid-phase microextraction (HS-SPME) using commercial fibers and an internally cooled SPME fiber device coupled to gas chromatography-mass spectrometry (GC-MS) was used to identify the volatile compounds of five tropical fruits. Pulps of yellow passion fruit (Passiflora edulis), cashew (Anacardium occidentale), tamarind (Tamarindus indica L.), acerola (Malphigia glabra L.), and guava (Psidium guajava L.) were sampled. The extraction conditions were optimized using two experimental designs (full factorial design and Doehlert matrix) to analyze the main and secondary effects. The volatile compounds tentatively identified included alcohols, esters, carbonyl compounds, and terpernes. It was found that the cold fiber was the most appropriate fiber for the purpose of extracting volatile compounds from the five fruit pulps studied.     

Application of a modified method for 3-mercaptohexan-1-ol determination to investigate the relationship between free thiol and related conjugates in grape juice and wine

A method has been developed for determining 3-mercaptohexan-1-ol (3-MH) in wine and grape juice using gas chromatography with conventional electron ionization (EI) mass spectrometry. The limit of quantitation of 40 ng/L was achieved with excellent precision using stable isotope dilution analysis (SIDA) combined with headspace solid-phase microextraction (SPME) of derivatized 3-MH. This method was used in combination with HPLC-MS/MS analysis of the individual diastereomers of 3-S-cysteinylhexan-1-ol (Cys-3-MH) and 3-S-glutathionylhexan-1-ol (Glut-3-MH), which are known precursors of the volatile thiol 3-MH. Commercial and small-lot winemaking trials were evaluated to determine the concentrations of precursors and free 3-MH at various stages of grape processing and winemaking. Five Sauvignon blanc clones were also assessed for precursors and free thiol during ripening, revealing the presence of 3-MH in the unfermented juices and a stark increase in precursor concentrations in the latter stage of ripening. Additionally, differences due to sample freezing and mode of juice preparation were revealed for the precursors, and a set of commercially available wines was analyzed to investigate the amounts of precursors and free 3-MH in Sauvignon blanc and other white wine varieties. There was seemingly no relationship between precursor concentrations in juice and 3-MH concentrations in wine. This was somewhat understandable, because the formation of precursors appears to be a dynamic process affected by a multitude of factors, beginning with grape ripening and continuing during vinification.     

Tequila volatile characterization and ethyl ester determination by solid phase microextraction gas chromatography/mass spectrometry analysis

Solid phase microextraction (SPME) and gas chromatography were used for tequila volatile characterization and ethyl ester quantitation. Several factors determined the differences in tequila volatile profiles obtained by the SPME technique, namely, sampling mode, fiber coating, and fiber exposure time. Each of these factors determined the most suitable conditions for the analysis of volatile profiles in tequila. Volatile extraction consisted of placing 40 mL of tequila in a sealed vial kept at 40 degrees C. A poly(dimethylsiloxane) fiber was immersed in the liquid for 60 min and desorbed for 5 min into the gas chromatograph. The identified volatiles by mass spectrometry were mainly alcohols, esters, and ketones. The calibration curves for ethyl hexanoate, octanoate, and decanoate followed linear relationships with highly significant (p < 0.001) determination coefficients (R2 = 0.99). The coefficients of variation of less than 10% for ethyl ester concentrations indicated that the technique was reproducible. The limits of quantitation for ethyl esters were 0.05 parts per million, which were below the concentration range (0.27-15.03 ppm) found for different tequila samples. Quantitative differences in ethyl esters were found for the four most commonly known tequila types: silver, gold, aged, and extra-aged.     

Stir bar sorptive extraction combined with GC-MS analysis and chemometric methods for the classification of South African Wines according to the volatile composition

A simple method for the analysis of major wine volatiles and semivolatiles by stir bar sorptive extraction in combination with thermal desorption and gas chromatography-mass spectrometry (SBSE-TD-GC-MS) was developed. Significant experimental parameters such as extraction time, temperature, salt addition, pH, and thermal desorption parameters were optimized to provide a sensitive and robust analytical method. The method provided good repeatability (%RSD < 10%) for 38 major wine volatile compounds, including alcohols, acids, esters, phenols, aldehydes, ketones, and lactones. Quantitative data for 62 South African red and white wines were used to study the suitability of major volatile data for the differentiation of wine samples according to grape variety or cultivar. Principal component analysis (PCA) and cluster analysis (CA) showed that most of the variation in volatile composition between wine samples could be ascribed to differences in wine age, wood contact, and fermentation practices. Despite the contribution of these factors, discriminant analysis (DA) was successfully applied to the classification of red and white wine samples according to cultivar.     

Metabolites of lesser grain borer in grains

Many volatile alcohol and ester metabolites of the lesser grain borer (LGB, Rhyzopertha dominica) cultured on wheat grain were identified. Volatiles from infested samples at 80 degrees C were collected on Tenax absorbent, thermally desorbed, and analyzed by gas chromatography (GC) using infrared (IR) and mass (MS) detectors for component identification. A solid-phase microextraction (SPME) technique was used to analyze selected samples with a GC-MS system set up for obtaining chemical ionization mass spectra. SPME was also used in a synthesis process required to identify ester metabolites. Predominant compounds in LGB-infested grains were 2-pentanol and its esters of 2-methyl-2-pentenoic (A) and 2,4-dimethyl-2-pentenoic (B) acids, which are known aggregation pheromones, dominicalures 1 and 2. 2-Pentanol esters of saturated A, beta-keto- and beta-hydroxy derivatives of A and B, homologues of A and B, and acid moieties lacking the 2-methyl substitution were found. Other straight- and branched-chain secondary alcohols and their esters were also observed. Reexamination of GC-MS-IR data acquired in previous investigations of LGB cultured on sorghum grain and commercial samples in a grain odor study showed the presence of many LGB metabolites in addition to the known dominicalures.     

Headspace solid phase microextraction (SPME) analysis of flavor compounds in wines. Effect of the matrix volatile composition in the relative response factors in a wine model.

The application of headspace solid phase microextraction (SPME) for flavor analysis has been studied. Headspace SPME sampling was tested for nine common wine flavor compounds in 10% (v/v) aqueous ethanol: linalool, nerol, geraniol, 3-methyl-1-butanol, hexanol, 2-phenylethanol, ethyl hexanoate, ethyl octanoate, and ethyl decanoate. The chemical groups (monoterpenoids, aliphatic and aromatic alcohols, and esters) showed specific behavior in SPME analysis. SPME sampling parameters were optimized for these components. Relative response factors (RRFs), which establish the relationship between the concentration of the compound in the matrix liquid solution and the GC peak area, were estimated for all compounds. Log(10)(RRF) varied from 0 (3-methyl-1-butanol) to 3 (ethyl decanoate), according to their molecular weight. Quantification by SPME was shown to be highly dependent on the matrix composition; the compounds with higher RRF were the less affected. As a consequence, the data obtained with this methodology should be used taking into consideration these limitations, as shown in the analysis of four monovarietal Bairrada white wines (Arinto, Bical, Cerceal, and Maria Gomes).     

Wine production using yeast immobilized on apple pieces at low and room temperatures

A biocatalyst was prepared by immobilization of Saccharomyces cerevisiae strain AXAZ-1 on apple pieces. It was examined by electron microscope and studied during the fermentation of grape must for batch wine-making. The immobilized yeast showed an important operational stability without any decrease of its activity even at low temperatures (1-12 degrees C). Specifically, at 6 degrees C the biocatalyst favored wine production within 8 days, which is less time than is required for the natural fermentation of grape must. At 1 degrees C wine production was effected in 1 month. This speeding up of the fermentation could be accepted and adopted by the industry for scaling up the wine-making process. Total and volatile acidities were similar to those found in dry wines. The concentrations of higher alcohols (propanol-1 and isobutyl alcohol) were low. The presence of amyl alcohols proved to be temperature dependent and decreased with the temperature decrease. The values of ethyl acetate concentrations were relatively high, up to 154 mg/L. This probably contributes to the fruity aroma and excellent taste of the produced wines. There was no indication of vinegar odor in the product given that the volatile acidity was <0.47 g of acetic acid/L. From the GC-MS analysis it was concluded that cell immobilization did not create serious changes in the product (wine) with regard to the qualitative composition of the aroma compounds.     

Factors limiting the synthesis of virgin olive oil volatile esters

The aim of the present work was to establish the limiting factors affecting the biosynthesis of volatile esters present in virgin olive oil (VOO). Oil volatile fractions of the main Spanish olive cultivars, Arbequina and Picual, were analyzed. It was observed that acetate esters were the most abundant class of volatile esters in the oils, in concordance with the high content of acetyl-CoA found in olive fruit, and that the content of C6 alcohols is limited for the synthesis of volatile esters during the production of VOO. Thus, the increase of C6 alcohol availability during VOO production produced a significant increase of the corresponding ester in the oils in both cultivars at two different maturity stages. However, the increase of acetyl-CoA availability had no effect on the VOO volatile fraction. The low synthesis of these C6 alcohols seems not to be due to a shortage of precursors or cofactors for alcohol dehydrogenase (ADH) activity because their increase during VOO production had no effect on the C6 alcohol levels. The experimental findings are compatible with a deactivation of ADH activity during olive oil production in the cultivars under study. In this sense, a strong inhibition of olive ADH activity by compounds present in the different tissues of olive fruit has been observed.     

戴尔有孢圆酵母调控晚采小芒森葡萄酒乙酸和香气

为降低甜型葡萄酒中的挥发酸,进一步增加其香气复杂度,该研究利用本土戴尔有孢圆酵母R12与酿酒酵母NX11424同时接种和顺序接种发酵,研究其对贺兰山东麓产区晚采小芒森葡萄酒乙酸及香气成分的调控。与酿酒酵母单菌发酵相比,本土戴尔有孢圆酵母与酿酒酵母按照5:1、20:1、50:1的不同菌体数量比例同时接种和间隔5d顺序接种发酵,均可以显著降低晚采小芒森葡萄酒的乙酸含量,其乙酸产率分别降低19.1%、21.2%、38.2%和48.9%。此外,按20:1比例同时接种发酵,可显著提高晚采小芒森葡萄酒中萜烯类和降异戊二烯类等品种香气物质含量,和乙酸异戊酯、丁酸乙酯及苯乙醇等发酵香气物质的含量。该研究表明合理的酿酒酵母接种发酵能有效降低高糖原料酿造葡萄酒挥发酸含量,为贺兰山东麓产区葡萄酒新产品的开发提供了的技术参考。     

不同酶和酵母对干红葡萄酒香气影响的差异分析

为提高甘肃河西产区蛇龙珠干红葡萄酒的香气品质,优化酿酒工艺,该文采用顶空固相微萃取和气相色谱-质谱联用技术,分析比较了添加不同浸渍酶和酵母发酵的蛇龙珠干红葡萄酒的香气构成。结果显示:蛇龙珠干红葡萄酒中初步定性香气化合物75种,主要为酯、醇、酸、萜烯和酚类物质。比较酯类、萜烯类等香气成分质量浓度和香气物质释放总量,EX-V酒样明显高于EX和HC酒样,D254酒样明显高于BDX酒样。各组酒样主要香气成分构成相似,但微量香气成分差异显著。果香是香气强度最高的香气系列,植物香、脂肪香、花香次之,其香气强度EX-V酒样高于EX和HC酒样,D254酒样高于BDX酒样。浸渍酶和酵母对甘肃河西产区蛇龙珠干红葡萄酒香气品质的影响评价显示,浸渍酶EX-V优于EX和HC,酵母D254优于BDX。研究结果可为甘肃河西产区蛇龙珠干红葡萄酒香气品质的提高及酿造工艺研究提供科学数据参考。     

加热处理对蜂蜜酒香气物质的影响

为研究适合蜂蜜酒发酵的优良工艺条件,以2批荆条蜜(白色和浅琥珀色)为原料,在酒精发酵前对发酵醪液进行加热处理,以不加热处理的样品为对照,采用酿酒酵母FX10进行发酵,发酵结束后测定蜂蜜酒的各项理化指标及挥发性化合物的含量。结果表明,供试酒样中共检测出77种挥发性物质,其中酯类39种、醇类20种、酸类8种、萜烯类4种、羰基化合物6种。加热处理可以显著增加蜂蜜酒中香气物质的种类和含量,含量较高的香气物质有乙酸乙酯、乙酸苯乙酯、乙酸异戊酯、己酸乙酯、辛酸乙酯、癸酸乙酯、月桂酸乙酯、9-十六碳烯酸乙酯、异戊醇、β-苯乙醇、辛酸和癸酸。对蜂蜜酒中香气物质进行主成分分析,发现加热处理的酒样中酯类物质对酒香贡献较大;对照酒样中酯类物质对酒香贡献较小,而醇类物质是其主要挥发性成分。本研究结果为蜂蜜酒的生产提供了一定的理论依据。     

Changes in the volatile compounds and chemical and physical properties of Kuerle fragrant pear (Pyrus serotina Reld) during storage

Volatiles from stored Kuerle fragrant pears (Pyrus serotina Reld) were studied using high-resolution gas chromatography and the solid-phase microextraction (SPME) method of gas chromatography/mass spectrometry (GC/MS). The dominant components were hexanal, ethyl hexanoate, ethyl butanoate, ethyl acetate, hexyl acetate, ethanol, alpha-farnesene, butyl acetate, and ethyl (E,Z)-2,4-decadienoate. By using GC-olfactometry, it demonstrated that the volatile compounds from SPME were responsible for the aroma of the Kuerle fragrant pear. The levels of sugars, organic acids, and phenolic acids in Kuerle fragrant pears were investigated using high-performance liquid chromatography (HPLC). Fructose was the dominant sugar, followed by glucose and sucrose. With increasing storage time, sucrose levels decreased; however, changes in fructose and glucose levels were not remarkable. There was a slight decrease in flesh firmness during storage. The general soluble solids concentration (SSC) declined slightly after 5 months storage. Some aroma-related volatile components increased during storage, while others decreased, especially the esters. The organic acids and phenolic acids also changed. The flavor of the Kuerle fragrant pears was affected by the change of volatile compounds and changes in chemical and physical properties.     

Sensory and analytical study of rose sparkling wines manufactured by second fermentation in the bottle

The sensory and analytical characteristics of five rose sparkling wines manufactured by the traditional method have been determined. Moreover, the changes that take place in the nitrogen and volatile fraction of the wines during the second fermentation and the aging with the yeasts have been studied. Each of these wines was made from a single industrial rose base wine of the Garnacha Tinta variety, with five selected yeasts strains. The base wine had a low content in free amino acids, 16 mg/L, and the yeast consumed more peptides than free amino acids during second fermentation. From the application of the two-way analysis of variance, yeast strain, and aging time factors to the data of volatile compounds, it has been found that most of the differences between these sparkling wines are due to the aging time. It has been verified that these rose sparkling wines have foam of good quality and that the grape variety Garnacha Tinta is suitable for the production of rose sparkling wines.