The mouth-feel properties of polysaccharides and anthocyanins in a wine like medium

Use of non-Saccharomyces wine yeasts as novel sources of mannoproteins in wine

Eight non-Saccharomyces wine strains, previously selected for their ability to modulate the final concentrations of various volatile compounds and to persist with Saccharomyces cerevisiae in mixed inocula fermentations of grape juice, have been analyzed in the present work to test their ability to release mannoproteins. The eight strains were members of different genera originally isolated from grape: Hansensiaspora osmophila, Lachancea thermotolerans, Metschnikowia pulcherrima, Pichia fermentans, Saccharomycodes ludwigii, Starmerella bacillaris, Torulaspora delbrueckii and Zygosaccharomyces florentinus. A synthetic polysaccharide-free grape juice, was used to characterize the mannoproteins released during the alcoholic fermentation. Mannoproteins profiles were characterized by gel electrophoresis and carbohydrate composition was analyzed both by HPLC and by mass spectrometry. The eight non-Saccharomyces yeasts demonstrated a higher capacity to release polysaccharides compared to S. cerevisiae. The proteins released by the eight yeast strains showed a wide variety of protein sizes, ranging from 25 kDa to greater than 250 kDa. The mass spectrometric profile of the N-glycans ranged from 1600 to 4000 Da and was characteristic for each strain. Detailed investigation of the degree of polymerization of released N-glycans revealed variable composition from 8 to 15 units of monosaccharides.

Changes in polysaccharide composition during sparkling wine making and aging

The evolution in polysaccharide composition and molecular weights during sparkling wine making and aging was studied for the first time in this work. Different autochthonous grape varieties from Spain (Verdejo, Viura, Malvası́a, Albarı́n, Godello, Garnacha and Prieto Picudo) were used to elaborate sparkling wines following the champenoise method. Principal component analysis showed differentiation of wines according to polysaccharide families. This differentiation was due to the process of aging on yeast lees, but not to the variety employed. The content of mannoproteins during aging was positively correlated (r = 0.792) with total polysaccharides from grapes. After six months of aging the highest content of mannoproteins and polysaccharides rich in arabinose and galactose was obtained. Also a shift to lower molecular weights was observed. The combination of these two characteristics could imply a better foam stability and thus sensory quality of sparkling wines.

Polysaccharide composition of Monastrell red wines from four different Spanish terroirs: effect of wine-making techniques

Monastrell wines made from grapes grown in four different Spanish "terroirs" (Cañada Judı́o, Albatana, Bullas, and Montealegre) were studied. Different wine-making techniques were also used, including different refrigeration techniques (prefermentative cold maceration and dry ice addition) and the addition of two different enzymes (β-galactosidase and commercial pectinase enzyme). The results pointed to significant differences in the Monastrell wine polysaccharide fractions according to the geographical origin of the grapes. The Rhamnogalacturonan II (RG-II) concentration was 2-fold higher in the Montealegre terroir than in the Bullas terroir. The use of enzymes also modified the polysaccharide content of the wines. RG-II levels were higher in the wines from three terroirs when commercial enzymes were added. The arabinose/galactose ratio of one of the wines was modified by the use of enzymes during wine-making, and some prefermentative cold maceration samples showed high values for several polysaccharides. This study shows the great importance of the "terroir effect" in the polysaccharide composition of wines.

Compositional and sensory characterization of red wine polymers

After isolation from red wine by means of ultrafiltration and gel adsorption chromatography, the composition of the highly astringent tasting high-molecular weight polymers was analyzed by means of HPLC-MS/MS, HPLC-UV/vis, and ion chromatography after thiolytic, alkaline, and acidic depolymerization and, on the basis of the quantitative data obtained as well as model incubation experiments, key structural features of the red wine polymers were proposed. The structural backbone of the polymers seems to be comprised of a procyanidin chain with (-)-epicatechin, (+)-catechin, (-)-epicatechin-3-O-gallate units as extension and terminal units as well as (-)-epigallocatechin as extension units. In addition, acetaldehyde was shown to link different procyanidins at the A-ring via an 1,1-ethylene bridge and anthocyanins and pyranoanthocyanins were found to be linked to the procyanidin backbone via a C-C-linkage at position C(6) or C(8), respectively. Alkaline hydrolysis demonstrated the polymeric procyanidins to be esterified with various organic acids and phenolic acids, respectively. In addition, the major part of the polysaccharides present in the red wine polymeric fraction were found not to be covalently linked to procyanidins. Interestingly, sensory evaluation of individual fractions of the red wine polymers did not show any significant difference in the astringent threshold concentrations, nor in the astringency intensity in supra-threshold concentrations and demonstrated the mean degree of polymerization as well as the galloylation degree not to have an significant influence on the astringency perception.

Sensory properties of wine tannin fractions: implications for in-mouth sensory properties

Different molecular structures of grape tannins have been shown to influence astringency, however, the in-mouth sensory effects of different molecular structures in red wine tannins remains to be established. The objective of this research was to assess the impact of wine tannin structure on in-mouth sensory properties. Wine tannin was isolated from Cabernet Sauvignon wines of two vintages (3 and 7 years old) and separated into two structurally distinct subfractions with liquid-liquid fractionation using butanol and water. The aqueous subfractions had greater mean degree of polymerization (mDp) and contained a higher proportion of epigallocatechin subunits than the butanol-soluble subfractions, while the older wine tannin fractions showed fewer epicatechin gallate subunits than the younger tannin fractions. The red wine had approximately 3:1 mass ratio of the aqueous and butanol tannin subfractions which approximated an equimolar ratio of tannin in each subfraction. Descriptive sensory analysis of the tannin subfractions in model wine at equimolar concentrations revealed that the larger, more water-soluble wine tannin subfractions from both wines were perceived as more astringent than the smaller, more hydrophobic and more highly pigmented butanol-soluble subfractions, which were perceived as hotter and more bitter. Partial least squares analysis indicated that the greater hydrophobicity and color incorporation in the butanol fractions was negatively associated with astringency, and these characteristics are also associated with aged wine tannins. As the larger, water-soluble tannins had a greater impact on the overall wine astringency, winemaking processes that modulate concentrations of these are likely to most significantly influence astringency.

Sensory quality and compositional characteristics of blackcurrant juices produced by different processes

Effects of enzymatic and non-enzymatic juice pressing on key orosensory and chemical quality factors of blackcurrant juices were studied in laboratory scale using berries of five different cultivars (Mortti, Mikael, Marski, Ola and Breed15). Enzymatic processing increased the juice yield by 10-22% and the content of various phenolic compounds in juice by 4-10-fold as compared to the non-enzymatic process. Higher intensity of the mouth-drying astringency of the enzyme-aided juice was the most significant orosensory difference between the processes. Juices of different blackcurrant cultivars varied in sweetness, sourness and bitterness. The most intensive sensory attributes of the juices were sourness and puckering astringency regardless of processing method. They correlated positively with each other and were contributed by acid content and pH. In enzyme-aided juices, the contents of flavonol glycosides and hydroxycinnamic acids were associated with mouth-drying astringency, and sugar/acid ratio correlated with sweetness. These correlations were less clear in non-enzyme juices possibly due to lower content of phenolic compounds and the high content of pectin.

Quantification and characterization of cell wall polysaccharides released by non-Saccharomyces yeast strains during alcoholic fermentation

In order to improve knowledge about the oenological characteristics of non-Saccharomyces yeast strains, and to reconsider their contribution to wine quality, we studied the release of polysaccharides by 13 non-Saccharomyces strains of different species (three wine yeasts, six grape yeasts, and three spoilage yeasts) during alcoholic fermentation in synthetic must. Three Saccharomyces cerevisiae strains were included for comparison. All of the non-Saccharomyces strains released polysaccharides into fermentation medium; the amount released depended on the yeast species, the number of cells formed and their physiological conditions. Normalizing the quantity of macromolecules released to the cell biomass revealed that most non-Saccharomyces strains produced a greater quantity of polysaccharides compared to S. cerevisiae strains after 7 and 14days of fermentation. This capacity was particularly expressed in the studied wine spoilage yeasts (Saccharomycodes ludwigii, Zygosaccharomyces bailii, and Brettanomyces bruxellensis). Chemical characterization of exocellular polysaccharides produced by non-Saccharomyces yeasts revealed them to essentially be mannoproteins with high mannose contents, ranging from 93% for S'codes. ludwigii to 73-74% for Pichia anomala and Starmerella bombicola. Protein contents varied from 9% for P. anomala to 29% for Z. bailii. These compositions were very similar to those of the S. cerevisiae strains, and to the chemical composition of the cell wall mannoproteins of different yeast species. The presence of galactose, in addition to mannose and glucose, in the exocellular polysaccharides released by Schizosaccharomyces pombe, confirmed the parietal nature of the polysaccharides released by non-Saccharomyces yeasts; only this species has a galactomannan located in the outer layer of the cell wall.

Influence of grape maturity and maceration length on color, polyphenolic composition, and polysaccharide content of Cabernet Sauvignon and Tempranillo wines

The aim of this paper was to study how maturity and maceration length affect color, phenolic compounds, polysaccharides, and sensorial quality of Cabernet Sauvignon and Tempranillo wines at three stages of grape ripening. Ripeness increased color extractability, phenolic compounds, and polysaccharide concentrations. Moreover, the proanthocyanidin mean degree of polymerization (mDP) and the percentage of prodelphinidins also increased with maturity, whereas the percentage of galloylation decreased. In general, wines from riper grapes contain higher proportions of skin proanthocyanidins. Color and anthocyanin concentration decreased when the maceration was longer, whereas polysaccharide and proanthocyanidin concentrations did the opposite. It was also detected that the mDP and the percentage of prodelphinidins decreased when the maceration was extended, whereas the percentage of galloylation increased. These data seem to indicate that proanthocyanidin extraction from seeds is clearly increased throughout the maceration time.

A simple method for total quantification of mannoprotein content in real wine samples

Mannoproteins released by yeast cells throughout the winemaking process contribute in several ways to improve wine quality. For this reason, some winemaking practices have been developed in order to increase the mannoprotein content of wine. However, monitoring of mannoprotein content of wine during these processes, or even mannoprotein quantification in the final wines, is an analytical problem not easily solved so far. Here, we report a simple and accurate method for mannoprotein quantification in wines. The method involves isolation of wine polysaccharides by size exclusion chromatography, acid hydrolysis, elimination of acid by weak anionic exchange solid phase extraction, and analysis of monosaccharides by ion exclusion HPLC. Advantages over previously existing methods include low sample volumes, possibility of parallel processing for multiple samples, absence of precipitation steps, and clear distinction between mannoproteins and other wine polysaccharides.

Anthocyanins and their variation in red wines. II. Anthocyanin derived pigments and their color evolution

Originating in the grapes, anthocyanins and their derivatives are the crucial pigments responsible for the red wine color. During wine maturation and aging, the concentration of monomeric anthocyanins declines constantly, while numerous more complex and stable anthocyanin derived pigments are formed, mainly including pyranoanthocyanins, polymeric anthocyanins produced from condensation between anthocyanin and/or flavan-3-ols directly or mediated by aldehydes. Correspondingly, their structural modifications result in a characteristic variation of color, from purple-red color in young red wines to brick-red hue of the aged. Because of the extreme complexity of chemical compounds involved, many investigations have been made using model solutions of know composition rather than wine. Thus, there is a large amount of research still required to obtain an overall perspective of the anthocyanin composition and its change with time in red wines. Future findings may well greatly revise our current interpretation of the color in red wines. This paper summarizes the most recent advances in the studies of the anthocyanins derived pigments in red wines, as well as their color evolution.

Anthocyanins and their variation in red wines I. Monomeric anthocyanins and their color expression

Originating in the grapes, monomeric anthocyanins in young red wines contribute the majority of color and the supposed beneficial health effects related to their consumption, and as such they are recognized as one of the most important groups of phenolic metabolites in red wines. In recent years, our increasing knowledge of the chemical complexity of the monomeric anthocyanins, their stability, together with the phenomena such as self-association and copigmentation that can stabilize and enhance their color has helped to explain their color representation in red wine making and aging. A series of new enological practices were developed to improve the anthocyanin extraction, as well as their color expression and maintenance. This paper summarizes the most recent advances in the studies of the monomeric anthocyanins in red wines, emphasizing their origin, occurrence, color enhancing effects, their degradation and the effect of various enological practices on them.

Effect of the aging on lees and other alternative techniques on the low molecular weight phenols of Tempranillo red wine aged in oak barrels

The effect of different alternative techniques to the traditional aging on lees on the low molecular weight phenolic compounds of red wines was study as well as their evolution during the aging in oak wood barrels for six months. The study was carried out with Tempranillo red grapes from two consecutive vintages. The techniques assayed were the traditional aging on lees with or without the addition of exogenous β-glucanase enzymes, the use of yeast derivative preparations also with or without the addition of exogenous β-glucanase enzymes, the micro-oxygenation applied together with the aging on lees, and the use of non-toasted oak wood chips. Hydroxycinnamic acids were the compounds most affected by these treatments, mainly in the wines treated with chips and commercial yeast derivative products, which showed higher concentrations of the free acids, compounds that play an important role in wine stabilization color since they can act as anthocyanin copigments. The differences found between the assayed treatments were more important in the 2007 vintage than in the 2008. However, a more significant effect of micro-oxygenation in the 2008 vintage was observed, which could be related to the fact that in this vintage the treatment was longer. In the 2008 vintage, the differences between treatments decreased along the aging in barrel. This vintage effect could be associated to the differences in the phenolic concentration of the initial wines. In this sense more research should be done to corroborate this fact.

Genetic mechanisms underlying the methylation level of anthocyanins in grape (Vitis vinifera L.)

BACKGROUND

Plant color variation is due not only to the global pigment concentration but also to the proportion of different types of pigment. Variation in the color spectrum may arise from secondary modifications, such as hydroxylation and methylation, affecting the chromatic properties of pigments. In grapes (Vitis vinifera L.), the level of methylation modifies the stability and reactivity of anthocyanin, which directly influence the color of the berry. Anthocyanin methylation, as a complex trait, is controlled by multiple molecular factors likely to involve multiple regulatory steps.

RESULTS

In a Syrah × Grenache progeny, two QTLs were detected for variation in level of anthocyanin methylation. The first one, explaining up to 27% of variance, colocalized with a cluster of Myb-type transcription factor genes. The second one, explaining up to 20% of variance, colocalized with a cluster of O-methyltransferase coding genes (AOMT). In a collection of 32 unrelated cultivars, MybA and AOMT expression profiles correlated with the level of methylated anthocyanin. In addition, the newly characterized AOMT2 gene presented two SNPs associated with methylation level. These mutations, probably leading to a structural change of the AOMT2 protein significantly affected the enzyme specific catalytic efficiency for the 3'-O-methylation of delphinidin 3-glucoside.

CONCLUSION

We demonstrated that variation in methylated anthocyanin accumulation is susceptible to involve both transcriptional regulation and structural variation. We report here the identification of novel AOMT variants likely to cause methylated anthocyanin variation. The integration of QTL mapping and molecular approaches enabled a better understanding of how variation in gene expression and catalytic efficiency of the resulting enzyme may influence the grape anthocyanin profile.

Exploration of phenomena contributing to the diversity of Oenococcus oeni exopolysaccharides

Many food-grade bacteria produce exopolysaccharides (EPS) that may modify the food texture or affect their survival rate during food processing. This is the case of O. oeni, a bacterial species who drives malolactic fermentation in wine. The five strains analyzed in the present study all display both isolated genes dedicated to homopolysaccharide synthesis and gene clusters potentially associated with heteropolysaccharide synthesis. The number of isolated glycosyltransferase gene present and the gene composition of one of the operons change from one strain to the other. The soluble EPS yields and the EPS monomer composition vary depending on the strain and or the medium composition. O. oeni appears as a bacterium able to synthesize both homo and heteropolysaccharides. This unique property has rarely been described. Moreover, the abundance of the genetic determinants associated with EPS metabolism suggests that it is very important for the adaptation of the bacteria to wine.

Flocculation and transcriptional adaptation to fermentation conditions in a recombinant wine yeast strain defective for KNR4/SMI1

KNR4 defective recombinant wine yeast strains were previously shown to oversecrete mannoproteins during alcoholic fermentation and, depending on the genetic background, to contribute to protein stability of white wines. We have tried to get a deeper insight into the consequences of KNR4 deletion in a wine yeast strain, from both a biological and an enological standpoint, and to understand the mechanisms leading to improved mannoprotein release. In fermentation experiments, followed by aging on lees, and compared to the parent strain, the recombinant strain shows increased release of mannoproteins during the fermentation but little increase during aging. Mannoprotein release by the recombinant strain takes place mainly during the fermentation step. In contrast, autolysis of the recombinant strain keeps going after aging for 78 days. In addition, the recombinant strain is moderately flocculent, which would be interesting for the production of sparkling wines. This might be related to changes in the expression of Flo1p-regulated genes. The new biological processes affected by KNR4 deletion in wine yeasts, as revealed by this transcriptomic study are flocculation, adaptation to anaerobiosis, oxidative stress response, and ethanol tolerance, as well as FKS1 overexpression; but no overexpression was detected for genes coding for major structural mannoproteins of the cell wall.

Characterization and antioxidant activity of the complex of tea polyphenols and oat β-glucan

Few data are available about the effects of complexation of polyphenols with polysaccharide on their bioavailability. The complex of tea polyphenols (TP) with oat β-glucan was characterized by ultraviolet-visible spectrometry, Fourier transform infrared spectrometry, differential scanning calorimetry, atomic force microscopy, and solid-state (13)C NMR spectroscopy. The results indicated that the bonds which governed the interaction between TP and oat β-glucan were strong hydrogen bonds. The in vitro antioxidant activity of TP, β-glucan, their complex, and physical mixture was assessed using four systems, namely, DPPH(•), OH(•), and O(2)(•-) scavenging activities and reducing power. The complexation and blending of TP and β-glucan exhibited different impacts on the index of in vitro and in vivo antioxidant capacities. In the concentration range of 0.5-2.5 mg mL(-1), the complex had highest O(2)(•-) scavenging activity, whereas the highest OH(•) scavenging activity was found with the physical mixture. For antioxidant testing in vivo, there was no significant difference between the complex and the physical mixture in terms of glutathione peroxidase activity and levels of malondialdehyde and total antioxidant capacity in serums. However, the complex exhibited much higher activities of superoxide dismutase and glutathione peroxidase in livers than the physical mixture. The present study provided a deeper understanding of the influence of molecular interaction between TP and oat β-glucan on their antioxidant activities.

Reconstitution of the flavor signature of Dornfelder red wine on the basis of the natural concentrations of its key aroma and taste compounds

By application of aroma extract dilution analysis (AEDA) on the volatile fraction isolated from a Dornfelder red wine, 31 odor-active compounds were identified by means of HRGC-MS and comparison with reference compounds. A total of 27 odorants, judged with high FD factors by means of AEDA, was quantitated by means of stable isotope dilution assays, and acetaldehyde was determined enzymatically. In addition, 36 taste-active compounds were analyzed by means of HPLC-UV, HPLC-MS/MS, and ion chromatography. The quantitative data obtained for the identified aroma and taste compounds enabled for the first time the reconstruction of the overall flavor of the red wine. Sensory evaluation of both the aroma and taste profiles of the authentic red wine and the recombinate revealed that Dornfelder red wine was closely mimicked. Moreover, it was demonstrated that the high molecular weight fraction of red wine is essential for its astringent taste impression. By comparison of the overall odor of the aroma recombinate in ethanol with that of the total flavor recombinate containing all tastants, it was shown for the first time that the nonvolatile tastants had a strong influence on the intensity of certain aroma qualities.

Quantitative colorimetric assay for total protein applied to the red wine Pinot noir

A standard method for assaying protein in red wine is currently lacking. The method described here is based on protein precipitation followed by dye binding quantification. Improvements over existing approaches include minimal sample processing prior to protein precipitation with cold trichloroacetic acid/acetone and quantification based on absorbance relative to a commercially available standard representative of proteins likely to be found in wine, the yeast mannoprotein invertase. The precipitation method shortened preparation time relative to currently published methods and the mannoprotein standard yielded values comparable to those obtained by micro-Kjeldahl analysis. The assay was used to measure protein in 48 Pinot noir wines from 6 to 32 years old. The protein content of these wines was found to range from 50 to 102 mg/L with a mean value of 70 mg/L. The availability of a simple and relatively rapid procedure for assaying protein provides a practical tool to quantify a wine component that has been overlooked in routine analyses of red wines.

Wine and grape tannin interactions with salivary proteins and their impact on astringency: a review of current research

Astringency is an important characteristic of red wine quality. The sensation is generally thought to be produced by the interaction of wine tannins with salivary proteins and the subsequent aggregation and precipitation of protein-tannin complexes. The importance of wine astringency for marketability has led to a wealth of research on the causes of astringency and how tannins impact the quality of the sensation, particularly with respect to tannin structure. Ultimately, the understanding of how tannin structure impacts astringency will allow the controlled manipulation of tannins via such methods as micro-oxygenation or fining to improve the quality of wines.

Optimization of adsorption of tea polyphenols into oat β-glucan using response surface methodology

Information on interactions between oat β-glucan and tea polyphenols (TP) is not available in the published literatures. Equilibrium dialysis was applied to determine the adsorption of TP into β-glucan, and response surface methodology (RSM) was employed to optimize the absorbing variables (pH, temperature, and phosphate buffered saline (PBS) buffer concentration). The equilibrium data at constant temperature were fitted with the Langmuir, Freundlich, and Redlich-Peterson models. The results showed that the Freundlich model was the best method to describe the experimental data. Parabolic curves were obtained for pH and temperature. In terms of adsorption capacity, factors including temperature, pH/temperature, and buffer concentration/temperature had the greatest influence on the response. The highest adsorption capacity of TP into β-glucan was 134.55 μg mg(-1) at the following optimized conditions: pH 5.56, PBS buffer concentration 0.13 M, and temperature 40 °C. No significant differences (p > 0.05) between the experimental and predicted values confirmed the adequacy of the response surface equations.

Interactions between yeast autolysates and volatile compounds in wine and model solution

The addition of a commercial yeast autolysate to a model solution of five typical wine aroma compounds (ethyl octanoate, linalool, 2-phenylethanol, β-ionone and octanoic acid) was investigated considering different variables, such as temperature, pH and the presence of highly concentrated natural volatile substances in wine (e.g. 3-methyl-1-butanol). The interactions of such compounds with both yeast walls and released colloids were studied using gas chromatography, with liquid-liquid extraction and solid-phase microextraction. The results were compared with those obtained by adding the commercial product to a white table wine, spiked with the five standard compounds. The data confirmed that yeast walls mainly bind less polar molecules: their loss in synthetic medium seemed to increase at higher pH values. Temperature and pH affected differently the interactions between yeast colloids and volatile compounds in wine and model solution: in complex solutions (as the addition of 3-methyl-1-butanol demonstrated) the interaction mechanisms could be influenced by competitive or other matrix-related effects, which can reduce the binding of single compounds, or even enhance their volatility.

Biosynthesis of anthocyanins and their regulation in colored grapes

Anthocyanins, synthesized via the flavonoid pathway, are a class of crucial phenolic compounds which are fundamentally responsible for the red color of grapes and wines. As the most important natural colorants in grapes and their products, anthocyanins are also widely studied for their numerous beneficial effects on human health. In recent years, the biosynthetic pathway of anthocyanins in grapes has been thoroughly investigated. Their intracellular transportation and accumulation have also been further clarified. Additionally, the genetic mechanism regulating their biosynthesis and the phytohormone influences on them are better understood. Furthermore, due to their importance in the quality of wine grapes, the effects of the environmental factors and viticulture practices on anthocyanin accumulation are being investigated increasingly. The present paper summarizes both the basic information and the most recent advances in the study of the anthocyanin biosynthesis in red grapes, emphasizing their gene structure, the transcriptional factors and the diverse exterior regulation factors.

Systematic identification of yeast proteins extracted into model wine during aging on the yeast lees

Total protein and protein-associated mannan concentrations were measured, and individual proteins were identified during extraction into model wines over 9 months of aging on the yeast lees following completion of fermentations by seven wine strains of Saccharomyces cerevisiae. In aged wines, protein-associated mannan increased about 6-fold (+/-66%), while total protein only increased 2-fold (+/-20%), which resulted in a significantly greater protein-associated mannan/total protein ratio for three strains. A total of 219 proteins were identified among all wine samples taken over the entire time course. Of the 17 "long-lived" proteins detected in all 9 month samples, 13 were cell wall mannoproteins, and four were glycolytic enzymes. Most cytosolic proteins were not detected after 6 months. Native mannosylated yeast invertase was assayed for binding to wine tannin and was found to have a 10-fold lower affinity than nonglycosylated bovine serum albumin. Enrichment of mannoproteins in the aged model wines implies greater solution stability than other yeast proteins and the possibility that their contributions to wine quality may persist long after bottling.

Effect of yeast strain and fermentation conditions on the release of cell wall polysaccharides

To improve our understanding of the factors involved in polysaccharide release during alcoholic fermentation, we investigated three Saccharomyces cerevisiae strains in fermentation trials conducted at two temperatures (25 degrees C and 32 degrees C) and three sugar concentrations (20%, 23.5%, and 27%), with or without supplementation of grape juice with diammonium phosphate (DAP) or microcrystalline cellulose. In two yeast strains, the release of cell wall polysaccharides increased significantly with an increase in fermentation temperature and sugar concentration of the grape juice; the polysaccharide release was greater in stressed conditions, in which the cells were less viable and less metabolically active. In the third strain, the average amount of polysaccharides released into the medium decreased significantly at 32 degrees C with 27% sugar, and increased in grape juice supplemented with DAP. Thus, this strain released more polysaccharides when conditions were nearer to optimal and the yeast cells were more viable and metabolically active. Our results suggest that the yeast strains released cell wall polysaccharides via different mechanisms, and that the cell wall integrity pathway may account for some of the differences in polysaccharide release among the strains.