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.     

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.     

Investigation of volatiles evolution during the alcoholic fermentation of grape must using free and immobilized cells with the help of solid phase microextraction (SPME) headspace sampling

A biocatalyst was prepared by immobilization of Saccharomyces cerevisiae strain AXAZ-1 on delignified cellulosic material (DCM). Repeated batch fermentations were conducted using these biocatalysts and free cells, separately, at temperatures of 20, 15, and 10 degrees C. Solid phase microextraction (SPME) was used in monitoring the formation of volatile alcohols, acetate esters, and ethyl esters of fatty acids. The kinetics of volatile production were similar for free and immobilized cells. In all cases immobilized cells showed a better rate of volatile production, which was directly connected to sugar consumption. The main difference observed was in propanol production, which increased with temperature decrease for the immobilized cells, whereas it remained constant for the free ones. In the case of immobilized cells significant amounts of esters were also produced. It is well-known that esters contribute to the fruity aroma of wine. It was also established that SPME is a very sensitive, accurate, and reliable technique and can be used without any reservation in the characterization of volatile constituents of wine.     

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.     

Storage of immobilized yeast cells for use in wine-making at ambient temperature

A comparative study of the storage and reuse of immobilized yeast cells on apple pieces, kissiris, and gamma-alumina was carried out. The immobilized biocatalysts were allowed to remain in the fermented alcoholic liquid after the end of each fermentation batch for extended periods at 30 degrees C before reactivation in batch fermentation for wine-making. The results showed that the biocatalysts were able to reactivate and ferment after successively increased periods of storage compared to free cell systems both on glucose medium and on grape must. In glucose medium, apple-, kissiris-, and gamma-alumina-supported biocatalysts reactivated after 120, 80, and 83 days, respectively. Possible storage periods for grape must were lower but remained high. Immobilized yeast biocatalyst on apple pieces produced wines with an improved volatiles composition compared to kissiris- and gamma-alumina-supported biocatalysts. There were no significant negative effects on the fermentation activity and volatile byproduct composition.     

Selection of yeast starter culture strains for the production of marula fruit wines and distillates

Juice of the Sclerocarya birrea subsp. caffra (marula) fruit was fermented by indigenous microflora and different commercial Saccharomyces cerevisiae yeast strains at different temperatures, namely, 15 and 30 degrees C. Volatile acids, esters, and higher alcohols were quantified in the wine and distillates, and the results were interpreted using a multivariate analysis of variance and an average linkage cluster analysis. Significant differences between 15 and 30 degrees C and also among yeasts with respect to volatile compounds were observed. Yeast strains VIN7 and FC consistently produced wines and final distillates significantly different from the other strains. A panel of tasters and marula and brandy producers was asked to select wines and distillates that had an acceptable and typical marula "nose". They were also asked to detect the differences among wines and distillates fermented with the same yeast strain at different temperatures.     

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.     

Low-temperature brewing by freeze-dried immobilized cells on gluten pellets

A biocatalyst, prepared by the immobilization of a cryotolerant strain of Saccharomyces cerevisiae on gluten pellets, was freeze-dried without any protecting medium and used for repeated batch fermentations of wort for each of the temperatures 15, 10, 5, and 0 degrees C. The fermentation time for freeze-dried immobilized cells was about 2-fold that of the corresponding time for wet immobilized cells on gluten pellets, and lower than the corresponding time for freeze-dried free cells, especially at 5 and 0 degrees C. Beers produced by freeze-dried immobilized cells contained alcohol levels in the range of 5.0-5.5% v/v, diacetyl concentrations lower than 0.5 mg/L, polyphenol concentrations lower than 145.5 mg/L, and free cell concentrations lower than 3 g/L. As a result, they had a very good clarity after the end of primary fermentation. The amounts of amyl alcohols were lower than 129.1 mg/L and reduced as the temperature was decreased. Ethyl acetate concentrations were found in the range of 22.1-29.2 mg/L, giving a very good aroma and taste in the produced beers.     

Low-temperature brewing using yeast immobilized on dried figs

Dried figs, following exhaustive extraction of their residual sugars with water, were used for immobilization of Saccharomyces cerevisiae AXAZ-1. The immobilized biocatalyst was used in repeated batch fermentations of glucose at 30 degrees C, where significant reduction of the fermentation time was observed, falling from 65 h in the first batch to 7 h after the sixth batch. Repeated fermentations of wort at room and low temperatures resulted in fermentation times that fell from 26 to 20 h and from 27 to 24 days at 18 and 3 degrees C, respectively. Ethanol and beer productivities were high, showing suitability of the biocatalyst for low-temperature brewing. Diacetyl concentrations were low (0.3-0.5 mg/L), and polyphenols were lower than in commercial products and decreased as the fermentation temperature was decreased (126-50 mg/L). Ethyl acetate concentrations increased from 53 to 88 mg/L as the temperature was decreased, while the concentration of amyl alcohols at 3 degrees C (58 mg/L) was lower than half of that at 18 degrees C (125 mg/L). The beers produced at the end of the main fermentation had a fine clarity and a special fruity figlike aroma and taste, distinct from commercial products and more intense than beers produced by cells immobilized on other food-grade supports (gluten pellets or delignified cellulosic materials). GC-MS analysis did not show significant differences in the qualitative composition of the aroma compounds of the beers produced by immobilized and free cells.     

Influence of prefermentative treatments to the major volatile compounds of Assyrtiko wines

A study of the volatile fraction of Assyrtiko wines, using gas chromatography coupled with olfactometry, was realized. Twenty-seven volatile compounds were identified as potent odorants, most of them originating from the fermentation process. Quantification of the major volatile compounds was realized developing a rapid analytical method based on fractionation of a 50 mL wine aliquot using C 18-reversed phase adsorbent. After elution of the volatile compounds with pentane-diethyl ether and concentration under nitrogen, the final wine extract was injected in a gas chromatography-flame ionization detection system. The method allows satisfactory determination of more than 15 volatile compounds of wine. The linearity of the method gave a typical r (2) between 0.990 and 0.999, while reproducibility ranged from 5.1 to 12.2% (as relative standard deviation) with 9.5% as the average. The method was applied to wines produced by Assyrtiko grapes (AOC Santorini), for two consecutive years, to compare the effect of skin contact prior to fermentation and the must clarification process. Direct press and skin contact wines were differentiated analytically; however, highly significant differences were not. Inversely, the differences found between direct press/clarified and nonclarified wines were significant. Wines produced by direct press and clarified must presented significantly higher levels of ethylic esters and fusel alcohol acetates but lower fusel alcohol levels, leading probably to more fruity wines. This difference, between clarified and nonclarified grape musts, was not significant in the case of the wines produced by skin contact of Assyrtiko berries. These findings were validated by preference sensory analysis tests.     

Changes in volatile flavor components of guava juice with high-pressure treatment and heat processing and during storage.

The changes in volatile flavor components of guava juice during pressure processing (25 degrees C, 600 MPa, 15 min), heat processing (95 degrees C, 5 min), and storage at 4 and 25 degrees C were evaluated by purge and trap/gas chromatography/mass spectrometry. Esters were the major volatile fraction in guava juice, and alcohols were the second. Pressure processing could maintain the original flavor distribution of the juice. Heat processing (95 degrees C, 5 min) caused decreases in the majority of flavor components in the juice when compared with freshly extracted juice. High-pressure treatment at 600 MPa for 15 min can effectively sterilize microbes but partially inactivate enzymes of guava juice; therefore, volatile components in pressure-treated juice gradually changed during storage periods. Pressure-treated guava juice showed increases in methanol, ethanol, and 2-ethylfuran with decreases in the other components during storage period. Nevertheless, the volatile distribution of 600 MPa treated guava juice was similar to that of freshly extracted juice when stored at 4 degrees C for 30 days.     

Changes in the polyphenolic and volatile contents of "fino" sherry wine exposed to ultraviolet and visible radiation during storage

Experiments of accelerated oxidation of "fino" sherry wines have been conducted at 25 degrees C and under the influence of UV-visible radiation (a xenon lamp of 1500 W). With the aim of determining the contribution of UV-vis radiation to the browning phenomenon, two types of glass bottles were employed: topaz bottles (with low values of transmittance in the UV-visible range) and transparent bottles. To identify significant differences between the wine before and after being subjected to the influence of the UV-vis radiation, the values of absorbance at 420 nm and the concentrations of various polyphenolic and volatile compounds were submitted to a multivariate variance analysis. Both factors considered (time and type of bottle) had a statistically significant effect on the values of absorbance at 420 nm and on the concentration of most of the polyphenolic compounds, whereas only the "time" factor was significant for volatile compounds. All wines showed losses in several polyphenolic compounds, which were more severe for the wines bottled in transparent glasses. However, these wines exhibited a lower degree of visual browning (abs 420 nm). In the case of volatile compounds, most of these presented increases during storage exposed to the influence of the UV-vis radiation.     

Evaluation of the thermally dried immobilized cells of Lactobacillus delbrueckii subsp. bulgaricus on apple pieces as a potent starter culture

The aim of the present study was to evaluate the impact of thermal drying of immobilized Lactobacillus delbrueckii subsp. bulgaricus on apple pieces on the use of the derived biocatalyst in whey fermentation. The thermally dried immobilized biocatalyst was compared to wet and freeze-dried immobilized cells, in respect to maintenance of cell viability and fermentation efficiency. The thermal drying process appeared to be more efficient on survival rate as an 84% of the cells used for immobilization survived the process, while the freeze-drying process led to a 78% rate. The thermally dried immobilized biocatalyst was used in 12 repeated batch fermentations of synthetic lactose medium and whey at 37, 45, and 50 degrees C in order to evaluate its metabolic activity. The high number of repeated batch fermentations showed a tendency for high operational stability. Fermentations continued for up to 2 months without any significant loss of metabolic activity. SPME GC/MS analysis of aroma-related compounds revealed the distinctive character of fermented whey produced by the thermally dried immobilized bacterium cells. The effect of storage at 4-6 degrees C for up to 165 days of the biocatalyst, held directly after drying and after repeated batch fermentations, on fermentation activity was also studied. After storage, reactivation in whey was immediate, and the immobilized biocatalyst was able to produce up to 51.7 g/L lactic acid at 37 degrees C. The potential of thermally dried immobilized L. delbrueckii as a starter culture for food production was subsequently evaluated.     

Volatile fatty acid production with alfalfa (Medicago sativa) and glucose in denitrifying soil at different temperatures

Summary A laboratory study was done to determine how, if at all, temperatures affect the production of volatile fatty acids and the rate of denitrification in soil. Glucose and alfalfa were compared as C substrates at temperatures of -2, 10, and 25°C under anaerobic conditions. At -2°C (soil not frozen), the denitrification rate was slow but was as rapid with alfalfa as glucose. This indicated that the production of volatile fatty acids by fermenters or other C substrates from alfalfa were adequate to sustain denitrifiers. No volatile fatty acids were apparently produced with glucose at -2°C whereas acetate and propionate were produced with alfalfa during the 26-day incubation period. During the 8-day incubation period at 10°C, there were also greater accumulations of acetate and propionate with alfalfa than with glucose. At 25°C, there was no major difference in the denitrification rate between glucose and alfalfa over a 4-day period. In a contrast to the other temperatures, more butyrate than propionate was produced at 25°C, especially with alfalfa. Acetate was the dominant volatile fatty acid produced and generally increased with temperature, especially after NO₃ exhaustion at 10 and 25°C. This indicated that acetate was a source of C for denitrifiers.     

Influence of fatty acids on wine foaming

The influence of fatty acids (free and bound as ethyl esters) on wine foaming was studied in different white wines and the corresponding sparkling wines. Moreover, from three of these wines the foam formed by CO(2) injection was separated, and two fractions were then obtained: foam wine (FW) and remainder wine (RW). In these fractions and the sparkling wines produced from them, foam properties and fatty acids were also determined. The free fatty acids C8, C10, and C12 were negatively correlated with foamability (HM), whereas the ethyl esters of hexanoic, octanoic, and decanoic acids were positively related to HM. The value of HM was directly proportional to the ratio of esterified to unesterified fatty acids. This was confirmed by the changes that occur in the esterification ratio during the second fermentation and aging. No influence was observed on either the Bikerman coefficient or the stability time of foam.     

Effect of antioxidant protection of must on volatile compounds and aroma shelf life of Falanghina (Vitis vinifera L.) wine

Two vinification methods involving different degrees of antioxidant protection of Falanghina must during prefermentative steps, and referred as HAMP (high antioxidant must protection) and LAMP (low antioxidant must protection), were compared in terms of fermentation performances of four different yeast strains, composition of the volatile fraction of wines at the end of alcoholic fermentation, and shelf life of wines during storage. The use of HAMP technology resulted in wines with lower volatile acidity and higher concentrations of medium-chain fatty acid ethyl esters, acetates, and volatile fatty acids. For two of the four strains a lower concentration of isoamyl alcohol was also observed. HAMP wines also revealed increased shelf life because of the higher concentration of odor active esters at the end of storage and better preservation of varietal aromas.     

Influence of aging conditions on the quality of red Sangiovese wine

A red Sangiovese wine was stored in barrels of different woods (oak and chestnut) and types (225-L "barriques" and 1000-L barrels) at 12 and 22 degrees C for 320 days to evaluate the effects of different aging conditions on wine quality. Chestnut barrels led to wines richer in phenolics, and which were more tannic, colored, and fruity. Oak barrels gave wines with more monomeric phenolics, but less astringent, with higher vanilla smell, and more harmonious. The type of barrel could be used as a parameter to regulate the extraction of wood components and the polymerization of monomeric phenolics. Storage at 22 degrees C favored the formation of polymerized phenolics and the increase of color density and color hue. The temperature produced less pronounced effects on aroma and taste, even if wines stored at 12 degrees C showed more harmony.     

Ellagic acid and flavonoid antioxidant content of muscadine wine and juice

Antioxidant properties of flavonoids and ellagic acid were characterized in eight wines and juices produced by various processing methodologies from red and white muscadine grape cultivars (Vitis rotundifolia). Juices and wines were produced by hot- and cold-pressed techniques, and additional wine was produced following on-hull fermentation for 3, 5, and 7 days. Chromatographic conditions were developed to simultaneously separate anthocyanins, ellagic acid, and flavonols and correlated to a measurement of overall antioxidant capacity (AOX), and their changes were monitored after storage for 60 days at 20 and 37 degrees C. Regression coefficients between concentrations of individual polyphenolics and AOX ranged from 0.55 for ellagic acid to 0.90 for kaempferol. Both red and white wines had higher AOX values after storage than juices made from an identical grape press, despite lower concentrations of individual polyphenolic compounds. Red wines fermented on-hull had higher initial concentrations of antioxidant polyphenolics as compared to a corresponding hot-pressed juice, but changes in AOX during storage were more affected by time than by storage temperature despite lower concentrations of flavonoids and ellagic acid present at 37 degrees C as compared to 20 degrees C. Oxidative or polymerization reactions significantly decreased levels of monomeric anthocyanins during storage with the greatest losses observed for delphinidin and petunidin 3,5-diglucosides. Processing methods for muscadine wine and juice production were important factors influencing concentrations of antioxidant flavonoids and ellagic acid, while the role of fermentation and time had the greatest influence on retention of AOX properties during storage.     

Phenolic and volatile composition of wines made from Vitis vinifera cv. Muscat lefko grapes from the island of Samos

A study of the phenolic and volatile composition of wines produced from the white cultivar Muscat lefko from the island of Samos was conducted. Dry, fortified, naturally sweet wines and mistelles (aged and nonaged) have been studied. The phenolic components (flavan-3-ols, hydroxycinnamates, and flavonols) were measured by high-performance liquid chromatography after solid phase extraction (SPE). The terpenes (free and glycosidically linked) were determined by the use of gas chromatography-mass spectrometry (GC-MS) after SPE. The fermentation aroma components were analyzed by GC-MS after liquid-liquid extraction. It was found that the dry wines contained lower amounts of most of the phenolics and higher quantities of terpenes and fermentation aroma compounds than the sweet wines. The aged mistelle wines contained lower levels of coutaric and caftaric acids, higher concentrations of the free acids, and markedly fewer free and bound terpenes and fermentation aroma components compared to the other sweet wines. The naturally sweet wine contained relatively increased amounts of phenolics, 2,3-butanediol, and glycosidically linked terpenes.