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Food Hydrocolloids 34 (2014) 202e207

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Food Hydrocolloids

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Foamability of Prosecco wine: Cooperative effects of high molecularweight glycocompounds and wine PR-proteins

Simone Vincenzi, Antonella Crapisi, Andrea Curioni*

Dipartimento DAFNAE and Centro Interdipartimentale per la Ricerca in Viticoltura ed Enologia (CIRVE), Università di Padova, via dell’Università 16,35020 Legnaro (PD), Italy

a r t i c l e i n f o

Article history:Received 1 June 2012Accepted 19 September 2012

Keywords:WineFoamProteinsGlycoproteinsYeastGrape

* Corresponding author. Tel.: þ39 049 8272624; faE-mail address: andrea.curioni@unipd.it (A. Curion

0268-005X/$ e see front matter � 2012 Elsevier Ltd.http://dx.doi.org/10.1016/j.foodhyd.2012.09.016

a b s t r a c t

Five Macromolecular fractions differing in molecular weight (M.W.) and composition were separatedfrom a Prosecco wine by ultrafiltration and Size Exclusion Chromatography (SEC) before and after 1 and18 months of wine ageing on yeast lees. The SEC fractions, combined or alone, were back added to theultrafiltered wine in order to assess their contribution to wine foamability. The results indicated that thehighest M.W. fraction, containing the wine glycocompounds and comprising the yeast mannoproteinswas that giving the highest foamability, whereas the wine proteins deriving from the grape berry did notfoam. However, the combination of all the fractions gave a foamability higher than that provided by theglycocompounds, indicating a cooperative effects between these latter and the proteins of grape origin.This result can be explained by hypothesizing a molecular interaction leading to the formation ofmacromolecular complexes able to interact with the gasewine interface.

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1. Introduction

Foam behaviour is the first characteristic that is observed by theconsumer after a sparkling wine is poured into the glass (Brissonnet& Maujean, 1991). The wines destined to produce the highestquality sparkling wines should be chosen not only for their flavourbut also for their foamability. Variations in chemical composition ofthe wines related to the variety, harvest and winemaking tech-niques affect the foaming properties of sparkling wines (Andrés-Lacueva, Gallart, Lopez-Tamames, & Lamuela-Raventos, 1996).Winemakers know that certain grape varieties give rise to wineswhich have better foaming properties than others and that sometreatments performed in the winery, such as bentonite fining, canalso affect wine foam quality (Marchal, Chaboche, Douillard, &Jeandet, 2002; Vanrell et al., 2007). The vast majority of the scien-tific papers on wine foams refer to the sparkling wines producedwith the so-called “Champenois method”, which is used to makeChampagne and Cava wines. This method involves a rather longperiod of wine ageing on yeast lees (at least 15 and 9 months forChampagnes and Cava, respectively), which is essential to deter-mine the organoleptic and chemical characteristics of the product.In contrast, no literature data can be found concerning the sparklingwines aged on lees for a short time, as those produced with the so-

x: þ39 049 8272929.i).

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called “bulk method” which is used in Italy to produce Prosecco,a sparkling wine of great and increasing economical importance.

Wine is a complex matrix containing many types of moleculeswhich can enhance or impair foam formation and stability andseveral studies have confirmed that the foam properties are relatedto the wine chemical composition. For example, a relationshipbetween the foaming properties of still wines and proteins, iron,copper and caprylic and capric fatty acids was found (Maujean,Poinsaut, Dantan, Brissonnet, & Cossiez, 1990) and it was alsodemonstrated that proteins, polysaccharides and iron are concen-trated in the foam of a Champagne base wine (Brissonnet &Maujean, 1991).

Of the different foam active substances, proteins were initiallyindicated as playing a major role because of their surface properties(Moreno-Arribas, Pueyo, Nieto, Martin-Alvarez, & Polo, 2000). Dueto the contemporary presence of hydrophilic and hydrophobicdomains, proteins can act as surfactants enhancing foaming andcontributing to bubblefilm strength and elasticity (Malvy, Robillard,& Deteurtre, 1994). Indeed, some authors reported a close rela-tionship between protein concentration and foam quality in spar-kling wines (Brissonnet & Maujean, 1993; Pueyo, Martin-Alvarez, &Polo, 1995). In addition, protein removal by the use of processingaids such as bentonite affects the wine foaming characteristics, thisphenomenon being particularly important because Champagne andCava winemakers often add bentonite to the wine in order tofacilitate the riddling process (Vanrell et al., 2007). In addition toproteins, also polysaccharides can contribute to the foaming

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properties of sparkling wines (Moreno-Arribas et al., 2000) andrecent studies have shown that glycoproteins rather than proteinsare the most prominent macromolecules responsible for foamformation and stability (Senée, Robillard, & Vignes-Adler, 1999).Among the wine glycoproteins, the yeast mannoproteins releasedduring fermentation and autolysis have been associated with theimprovement of the foaming properties of sparkling wines (Nuñez,Carrascosa, Gonzalez, Polo, & Martinez-Rodriguez, 2005).

Very recently, reconstitution experiments performed by addingin amodel solution different molecular fractions isolated fromwineindicated that a synergistic effect in foamability and foam stabilityexists between high and low molecular weight wine compounds(Coelho, Reis, Domingues, Rocha, & Coimbra, 2011) and that thefraction most responsible for foaming is that comprising the yeastmannoproteins (Coelho, Rocha, & Coimbra, 2011). However, thespecific contribution to wine foaming of the purified wine proteinsof grape origin was not defined.

The aim of this paper is to study, by reconstitution experiments,the foaming of a Prosecco wine, before and after ageing on yeastlees, in relation to the effects of macromolecular fractions differingin M.W. and composition.

2. Materials and methods

2.1. Wines

A base wine from Glera grapes (Prosecco) (vintage 2009 wasused. The base wine was produced by standard white wine vinifi-cation, without bentonite treatment or protein fining. Fifty litres ofbase wine were used for the second fermentation after addition of10 g/L saccharose, 0.4 mg/L thiamine, 0.1 g/L ammonium phosphateand 0.5 mg/L copper sulphate. The commercial yeast DV10 (Lalle-mand, Castel d’Azzano, Italy) was prepared following the manu-facturer instructions and inoculated at 10 g/hL. The wine wasbottled in standard 0.75 L bottles and stored at 18 �C in horizontalposition. At the end of the second fermentation the bottles wereturned in vertical position in order to allow yeast sedimentation atthe bottom. The wines were never treated with bentonite, to followthe behaviour of the natural protein content during wine ageing.

2.2. Purification of wine macromolecules

At each sampling time, thewine of the six bottles wasmixed andfiltered first with GF/A filters (Whatman, Milan, Italy) and finallywith 0.45 mm cellulose acetate filters (Millipore, Vimodrone, Italy).An aliquot of the filtered wine (300 ml) was stored under nitrogenatmosphere for further analysis, whereas 3.5 L were concentratedby ultrafiltration (3.5 kDa cut off) by an Amicon 8400 (Millipore)apparatus under a constant nitrogen pressure of 3.5 bar. Theultrafiltered wine (permeate) was stored in 0.75 L bottles undernitrogen atmosphere and at 16 �C.

When the retentate volume reached about 50 ml, 1 L of modelwine (5 g/L tartaric acid, 12% ethanol, pH 3.2) was added to washout the remaining small molecules and the resulting permeate wasdiscarded. Ultrafiltration was continued until the retentate volumereached 5e10 ml. After concentration the wine, initially clear,became slightly turbid. This turbidity was removed by centrifuga-tion at 14,000 � g for 5 min, yielding a brown pellet and a yellowand viscous supernatant.

2.3. Size Exclusion Chromatography (SEC)

SEC was performed on an AKTA Purifier FPLC apparatus (GE-Healthcare, Milan, Italy) equipped with a 280 nm UV detector anda conductimeter. A Superdex 75 prep grade (Amersham, Milan,

Italy) column (separation range between 3 and 70 kDa) was used.Model wine (5 g/L tartaric acid, 12% ethanol, pH 3.2) at a flow of1.5 ml/min was used as the mobile phase.

Fiveml of concentratedwine (corresponding to 2.75 L of startingwine) was loaded on the column and 6 ml fractions were collected.On the basis of the UV chromatogram, the collected fractions werecombined in 5 pools (SEC fractions 1e5). SEC fractions 1e5 wereagain concentrated to 1.5 mL by ultrafiltration (3.5 kDa) asdescribed above.

2.4. Protein quantification

Protein content was determined according to Vincenzi et al.(2005). Firstly, proteins were precipitated from 1 mL of wine with10 mL of 10% SodiumDodecyl Sulphate (SDS) followed by addition of250 mL of 1 M KCl. The pellets were dissolved in 1 mL of distilledwater and quantified with the BCA-200 protein assay kit (Pierce,Rockford, IL) according to the manufacturer instructions. The cali-bration curvewas prepared by using serial dilution of bovine serumalbumin (BSA, Sigma, Milan, Italy) in water.

2.5. Polysaccharides quantification

The polysaccharide content was measured colorimetricallyaccording to Segarra, Lao, Lopez-Tamames, and Torre-Boronat(1995). Absorbance values were determined at 490 nm. The cali-bration curve was prepared by using serial dilution of glucose(Fluka, Milan, Italy) in water.

2.6. Sodium Dodecyl Sulphate-Polyacrylamide Gel Electrophoresis(SDS-PAGE)

SDS-PAGE analyses were performed according to Vincenzi andCurioni (2005) in non reducing conditions. Five ml of concentratedwine (before SEC) and SEC fractions (corresponding to 10 ml ofwine) were diluted with 20 ml of 0.5 M TriseHCl pH 6.8 buffercontaining 15% (v/v) glycerol and 1.5% (w/v) SDS (Bio-Rad labora-tories, Segrate, Italy) (loading buffer) and heated at 100 �C for 5minbefore loading. Electrophoresis was performed in a Mini-Protean IIIapparatus (Bio-Rad) in 14% polyacrylamide gels. The molecularweight standard proteins were the Broad Range Molecular WeightMarkers (Bio-Rad). Gels were stained for 18 h with colloidal Coo-massie and then de-stained with water for 24 h. The Periodic Acid-Schiff (PAS) method was used to stain glycocompounds asdescribed by Segrest and Jackson (1972).

2.7. Foam measurement

Foam parameters were measured with a classical Rudin tube(Rudin, 1957), closed at the bottom with a sintered glass plate(porosity 40e60 mm). The analysis were performed on the wholeand ultrafiltered wines.

In addition, concentrated SEC fractions were back added, aloneor combined, to the corresponding ultrafiltered wine at the originalconcentration. Foamability measurements were then performed onthe resulting reconstitutedwines. Before each analysis the tubewascleaned with ethanol, than rinsed three times with deionised waterand three times with the sample to be analysed. One hundredml offiltered sample (base, ultrafiltered or reconstituted wines) wereplaced in the tube and CO2 was sparged at a constant flow rate(260 ml/min) and pressure (300 kPa) from the bottom. The foamheight (FH) was measured every 15 s for 15 min, then the gas flowwas stopped and the foam decay was monitored. Each sample wasanalysed in triplicate.

S. Vincenzi et al. / Food Hydrocolloids 34 (2014) 202e207204

3. Results and discussion

Prosecco is an economically important sparkling wine which ismainly appreciated for its lightness, freshness and aroma, but alsofor its effervescence and foaming properties. The foaming proper-ties of a sparkling wine are the first characteristic perceived by theconsumer when the wine is poured in the glass and therefore theyaffect the overall appreciation of the wine quality (Brissonnet &Maujean, 1991). For these reasons the mechanisms and thefactors involved in foamability of this particular wine need to beinvestigated.

A Prosecco wine was studied before (base wine) and after thesecondary fermentation, that was performed in bottles in order toobtain the so-called “prise de mousse”. After the secondaryfermentation, which was complete after about 25 days, the wineswere maintained in contact with the yeast lees and used for theexperiments after 1 and 18 month of ageing. One month ageing onlees can be considered as representative of the winemaking tech-nique employed for the production of the most common Proseccowine with the so-called “bulk”method, which involves only a shortperiod of contact with the yeast lees. However, longer times ofageing could be also used because in that way different quality andtechnological properties can be achieved.

Since wine macromolecules are considered the most importantfactors determining wine foaming, the foaming effects of differentProsecco wine macromolecules and their variations during ageing(0, 1 and 18 months of contact with the yeast lees) were studied.Wine compounds with molecular weight (M.W.) larger than3.5 kDa were separated from the wines and fractionated by SizeExclusion Chromatography (SEC), thus obtaining the chromato-grams shown in Fig. 1. In each experiment, three main peaks wereobtained, although some differences in peak area and separationcould be noticed, confirming that a variation of the relative quan-tities of the different macromolecules of the wine occurred duringthe time of the experiments.

On the basis of the chromatograms, the collected fractions werecombined in five main pools (SEC fractions 1e5, Fig. 1), which wereanalysed by SDS-PAGE (Fig. 2). In all the cases the fractionsbelonging to the first SEC peak (fractions 1 and 2) showed a mainband at about 66 kDa (Fig. 2a), which, on the basis of previouslypublished data could be ascribed to the vacuolar invertase of thegrape berry (Jegou et al., 2009; Puff, Marchal, Aguié-Béghin, &Douillard, 2001). In addition to other minor bands, SEC fractions

Fig. 1. Size Exclusion Chromatography (SEC) of the concentrated Prosecco wines(retentates, >3.5 kDa) before (base wine) and after 1 and 18 months of ageing on yeastlees.

1 and 2 displayed some highM.W.material blocked at the top of thestaking gel, which tended to became more evident after wineageing on lees (Fig. 2a). This material showed to contain a highquantity of sugars when the gels were stained for the presence ofthese compounds (Fig. 2b), confirming previous findings (Marchal,Bouquelet, & Maujean, 1996). On the basis of these results, the highM.W. glycocompounds present in fractions 1 and 2 could be iden-tified as the yeast mannoproteins which are released in winesduring fermentation and ageing on lees due to the autolysis process(Gonçalves, Heyraud, De Pinho, & Rinaudo, 2002). These compo-nents are characterised by having molecular weights up to 560 kDa(Gonçalves et al., 2002), a negative charge due to the presence ofmannosylphosphate (Vernhet, Pellerin, Prieur, Osmianski, &Moutounet, 1996) and are present in wines in different quantitiesaccording to the yeast strain, the fermentation conditions and thetime of contact with the wine (Giovani, Canuti, & Rosi, 2010; Roweet al., 2010).

The results were confirmed by quantification of the sugarspresent in SEC fractions 1e5 (Fig. 3), which indicated that somevariations in the sugar content of the fractions occurred with thetime of ageing on lees. In particular the first eluting SEC fraction 1was enriched in high M.W. sugar compounds at 18 months, con-firming that the yeast autolysis process contributes to the enrich-ment of the wine in cell wall glycocompounds (Gonçalves et al.,2002).

Due to the similarity of the SDS-PAGE patterns of fractions 1 and2, these latter were combined to be used in foaming experiments.

While SEC fractions 3 showed in most of the cases to becomposed by protein bands belonging to the previous and thesubsequent fractions, SEC fraction 4 showed to mainly containprotein bands with an electrophoretic mobility (Mr) in the rangefrom 18 to 31 kDa. These components mainly derive from the grapeberry, corresponding to the typical major proteins of white wines,comprising Thaumatin-like (TL) proteins and chitinases (Waters,Wallace, & Williams, 1992). It is interesting to note that after 18months of ageing, some faint glycosylated bands appeared with Mrsimilar to those of the grape proteins (Fig. 2b). These bands arelikely to correspond to fragments generated from glycoproteinsdegradation occurring with the time (Moreno-Arribas, Pueyo, Polo,& Martin-Alvarez, 1998).

The effect of the different SEC fractions onwine foamability wasthen studied by adding the SEC fractions, individually or combined,to the corresponding ultrafiltered wines. Wine foamability wasmeasured as the maximum height (FH) reached by the foam duringthe gas sparging experiments.

As expected, the ultrafiltered wines, which were totallydeprived of molecules larger than 3.5 kDa, did not produce anymeasurable foam confirming that the foamability of the wines isdue to the presence of macromolecules (Aguié-Béghin et al., 2009).Initially the concentrated wine (retentate from the wine ultrafil-tration step) was diluted with ultrafiltered wine (permeate fromthe wine ultrafiltration step) to reach the same volume of theoriginal wine used for ultrafiltration. The foams produced by thesereconstituted samples were lower than that of the original wines(Fig. 4), indicating that the concentration process was likely toreduce the content of macromolecules. Actually, during theconcentration step the wines, initially clear, became slightly turbid.The insoluble material, which was necessarily removed by centri-fugation in order to avoid SEC column clogging, probably containedsome foam active compound. However, no differences in the SDS-PAGE patterns were detectable between the insoluble materialand the total wine (not shown), suggesting that the precipitationdid not involve specific components.

The contemporary addition of all the SEC fractions 1e5 to theultrafiltered wine restored a foamability similar to that obtained by

Fig. 2. Sodium Dodecyl Sulphate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) analysis of fraction 1e5 collected from SEC separation of the wine macromolecules with M.W.larger than 3.5 kDa (see Fig. 1). Gels were stained for proteins (a) and for sugars (b).

S. Vincenzi et al. / Food Hydrocolloids 34 (2014) 202e207 205

adding to the ultrafiltered wine the total concentrated winemacromolecules (Fig. 5). This result indicated that most of thecomponents responsible for foamability were present in the SECfractions. These fractions were then individually back added to theultrafiltered wine at the same concentration they were initiallypresent in the original wine in order to assess their specificcontribution to wine foamability (Fig. 5). As observed for the orig-inal wines (Fig. 4), the foamability decreased with the time of wineageing on lees, when both the total concentrated wine macromol-ecules and the combined SEC fractions were tested. The loss offoamability during the ageing time has been already described forwines produced with the “Champenois” method, being probablyrelated to the modification of the chemical composition of thewines during the contact with yeast lees (Andrés-Lacueva et al.,1996; Moreno-Arribas et al., 2000) or with the loss of amphiphilicmacromolecules which adsorb to the glass of the bottle duringstorage (Abou Saleh, Aguié-Beghin, Foulon, Valade, & Douillard,2007).

The foamability results (Fig. 5) indicated that the fractions withthe strongest effect on foam height were the high M.W. fraction1 þ 2, which was that containing the vast majority of the glyco-compounds, as assessed by both PAS staining of the SDS-PAGE gels(Fig. 2b) and sugar quantification (Fig. 3). This confirms that thesemacromolecules play a major role in wine foam formation(Brissonnet & Maujean, 1991; Coelho, Rocha, et al., 2011;Dambrouck, Marchal, Cilindre, Parmentier, & Jeandet, 2005;Moreno-Arribas et al., 2000). The glycocompounds detected afterSDS-PAGE comprised mainly high M.W. material blocked at the topof the gel, ascribable to yeast mannoproteins, and the 66 kDa grapeinvertase (Fig. 2). This enzyme, representing one of the most

Fig. 3. Sugar content of the SEC fractions (1e5) in the Prosecco wines before (basewine) and after 1 and 18 months of ageing on yeast lees.

abundant protein inwine (Dambrouck et al., 2005; Puff et al., 2001),due to its high content of hydrophilic sugars and relatively highhydrophobicity has good surface properties and then an importantrole in wine foam formation and stability has been suggested forthis component (Marchal et al., 1996). As amatter of fact, removal ofinvertase from wine has been shown to result in an impairment ofthe foam quality (Dambrouck et al., 2005). However, it has alsobeen reported that invertase alone is not a good model for themacromolecules involved in foam formation in champagne wines(Puff et al., 2001), thus giving rise to contrasting opinions on therole played by this protein in foaming. Yeast mannoproteins, whichcan be considered as proteoglycans due to the low content ofprotein, which is around 10% by weight (Gonçalves et al., 2002), arealso involved in foam formation and stabilisation, being able tointeract with the bubble walls due to the hydrophilicity of theirglycans (Coelho, Reis, et al., 2011; Nuñez et al., 2005; Nuñez,Carrascosa, Gonzales, Polo, & Martinez-Rodriguez, 2006; Senéeet al., 1999).

However, it must be noticed that glycan-rich fraction 1 þ 2 wasnot able, when added alone, to restore the volume of the foamformed when all the combined SEC fractions were added to theultrafiltered wine (Fig. 5), indicating that compounds present in theother fractions are also involved in determining the foamability ofthe wine.

SEC fraction 3 comprised components present in both thepreceding and the following SEC fractions (Fig. 2). Therefore, if the

Fig. 4. Foamability (foam height, FH) of Prosecco wines and of the permeates (utra-filtred wine) and the retentates (retentate) obtained after concentration of the winesby ultrafiltration. The retentates were back added to the ultrafiltered wine at the sameconcentration as in the starting wine.

Fig. 5. Foamability (foam height, FH) of the different SEC fractions (1e5) of the Pro-secco wine before (Base wine) and after 1 and 18 months of ageing on yeast lees.Fractions were back added combined (All fractions) or individually to the sameultrafiltered wine (permeate) from which they had been separated. The data obtainedfor the reconstituted wine, obtained by back adding the retentate to the permeateresulting from wine ultrafiltration (3.5 kDa) (Retentate) are also reported forcomparison.

S. Vincenzi et al. / Food Hydrocolloids 34 (2014) 202e207206

use of this fraction in the reconstitution experiments was necessaryto establish the effects of all the macromolecules recovered fromthe wine, the relationships between the effects on foam and thecomposition of SEC fraction 3 cannot be established.

In contrast, SEC fractions 4, which contained almost exclusivelythe wine PR-proteins of grape origin (Fig. 2a), when added alone tothe corresponding ultrafiltered wines showed a very low effect onfoam volume in the base wine, that was almost totally lost afterwine ageing on lees (Fig. 3). This indicates that the grape proteinsalone do not foam, although present in white wines in relativelyhigh quantities (Vincenzi et al., 2005). It is worth noting that in thesame experimental conditions, a different protein, such as BovineSerum Albumin (BSA) at the concentration of 20mg/L showed goodfoaming behaviour (Fig. 6).

Also the last eluting SEC fraction 5, despite the presence, inaddition to proteins similar to those of SEC fraction 4 (Fig. 2a), ofsome glycosylated compounds (in particular in thewine aged for 18months, Figs. 2b and 3) had no effects on foamability when addedalone to the corresponding ultrafiltered wines (Fig. 5).

A similar reconstitution experiment, but performed in a modelwine solution, was reported by Coelho, Rocha, et al. (2011) usingwine macromolecular fractions separated by different chromato-graphic steps. It was found that the supernatant obtained after C18separation, containing most of the high M.W. material, was thatgiving the highest foamability and some sub-fractions obtainedfrom that supernatant, including one containing 64% protein, wereresponsible for that foaming activity. However no fractions

Fig. 6. Comparison of the foamability curve obtained by the gas sparging method withBSA and SEC fraction 4 dissolved in ultrafiltered wine at 20 mg/ml.

containing the wine PR-proteins of grape origin, as the SEC fraction4 here described, were identified and tested for their foamingability.

The lack of foamability of the grape proteinsmay be relatedwiththeir structural characteristics. Indeed, most of the grape proteinsremaining in wines, which mainly belong to chitinases and TLproteins (Waters et al., 1992) have a compact and relatively rigidstructure which is stabilised by disulphide bonds. This type ofstructure is related to the function of these PR-proteins, which areinvolved in the defence of the plant against pathogens and thereforeneed to be particularly resistant to unfolding and denaturation. Thepossibility to unfold at the gaseliquid interface can be consideredan important phenomenon in determining the possibility fora protein to act as a surfactant, because, after unfolding, the expo-sition of the hydrophobic domains to the gas phase is maximised(Martin, Grolle, Bos, Stuart, & van Vliet, 2002). Therefore, theintrinsic structural resistance of the wine PR-proteins to undergoconformational changesmay be the reason for the difficulty of thesecomponents to unfold in the presence of the liquideair interfacewhen bubbles are formed in the wine and then to act as foamforming agents.

However, notwithstanding the intrinsic lack of foamability ofthe grape proteins, their presence in the mixture of the SEC frac-tions 1e5 contributed to wine foamability. As a matter of fact, thismixture gave a foamability (measured as FH) higher than that ob-tained by adding the FH values given by the individual SEC fractions(Fig. 5), suggesting a cooperative effect among the glycosylatedmaterial of the first eluting fractions and the wine PR-proteins ofgrape origin. The mechanism involved in determining this effect isnot known. However, the possible presence of protein complexesconstituted by the high M.W. glycocompounds and the grapeproteins at the aireliquid interface resulting in the formation of anadsorption layer would explain the cooperative effect in deter-mining wine foamability. These complexes may be generated bythe interactions of the negative charge of the yeast mannoproteins(Vernhet et al., 1996) and the positive charge of the grape PR-proteins, which, at the wine pH, are below their isoelectric point(Marchal et al., 1996). As a matter of fact the presence of bothglycocompounds and protein material deriving from macromo-lecular fractions of different M.W. in the adsorption layer of thefoam of Champagne wines has been recently reported (Abdallah,Aguié-Béghin, Abou-Saleh, Douillard, & Bliard, 2010) and thepresence of aggregated materials involving yeast glycoproteins andother unidentified wine components has also been indicated ascontributing to the foam activity of Champagne wines (Senée et al.,1999). Further research is needed to confirm the existence of theseaggregates in our experimental condition.

A technological aspect which should be mentioned concerns thepractical effects of bentonite treatments on wine foaming proper-ties. Bentonite treatments are commonly applied to white wines inorder to remove the proteins responsible for wine haze formationafter bottling, a defect that seriously impairs wine quality. Themainproteins involved in this defect are the PR-proteins of the grapeberry. Bentonite treatments have been shown to result in a loss ofwine foamability (Marchal et al., 2002) and this loss has beenascribed to the removal of the wine proteins, including invertase,but also the 20e30 kDa PR-proteins (Vanrell et al., 2007). Accordingto the results here reported, the removal of these PR-proteins,which do not foam by themselves, would abolish their coopera-tive effects in determining the foamability of sparkling wines.

In conclusion, as demonstrated here by reconstitution experi-ments in a real wine system, the macromolecular fraction con-taining the high M.W. glycocompounds is that with the highestcapacity to foam also in Prosecco wine whereas the wine PR-proteins deriving from the grape berry do not show foaming

S. Vincenzi et al. / Food Hydrocolloids 34 (2014) 202e207 207

activity. However, these latter components, when present in themacromolecular mixture of the wine, can increase its foamabilityby cooperating with the most foam-forming glycocompounds.Therefore, since these effects are likely to be present also in spar-kling wines deriving from other grape varieties, the content of bothglycocompounds and grape PR-proteins, as affected by the wine-making technology, should be carefully considered for their impacton wine foaming properties.

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