Grape and wine proteins: their fractionation by hydrophobic interaction chromatography and identification by chromatographic and proteomic analysis

Influence of flash heating and aspergillopepsin I supplementation on must and wine attributes of aromatic varieties

The protein instability with haze formation represents one of the main faults occurring in white and rosé wines. Among the various solutions industrially proposed, aspergillopepsin I (AP-I) supplementation coupled with must heating (60-75 °C) has been recently approved by OIV and the European Commission for ensuring protein stability of wines. This study investigates the impact of AP-I either applied independently or in combination with flash pasteurization on the chemical composition of grape must and wines derived from Sauvignon Blanc and Gewürztraminer. The efficacy on protein stability of a complete treatment combining heat (70 °C) and AP-I (HP) was confirmed through heat test and bentonite requirement, although no differences were observed between must heating and HP treatments. However, high-performance liquid chromatography analysis of unstable pathogenesis-related proteins revealed that AP-I supplementation reduced chitinases and thaumatin-like proteins compared to the non-enzymed samples, with and without must heating. Amino acid increase was reported only in HP musts, particularly in Sauvignon Blanc. The concentration of yeast-derived aroma compounds in Gewürztraminer wines was increased by must heating; compared to controls, flash pasteurization rose the overall acetate esters content of 85 % and HP of 43 %, mostly due to isoamyl acetate. However, heat treatments -with or without AP-I- reduced terpenes up to 68 %. Despite the different aroma profiles, no differences were observed for any descriptor for both varieties in wine tasting, and only a slight decrease trend was observed for the floral intensity and the typicality descriptors in heated wines.

Complexity of the effects of pre-fermentation oxygenation, skin contact and use of pectolytic enzymes in white winemaking as revealed by comprehensive proteomics and volatilomics analysis

Ion exchange chromatography and SDS-PAGE followed by identification by MALDI-TOF/TOF, and two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC-TOF-MS) were used for comprehensive proteomics and volatilomics evaluation of the effects of pre-fermentative oxygenation, skin contact and use of pectolytic enzymes in production of Malvazija istarska white wine, respectively. Many protein species and an unprecedented number of volatiles have been identified and (semi)quantified, revealing high complexity of the observed effects. Compared to a standard control wine, oxygenation treatment modulated the protein composition and resulted with a volatilome characterized by decreased levels of several important volatiles. Skin contact treatments, especially in combination with pectolytic enzymes, significantly increased the levels of a large number of proteins, but were also deprived of particular protein species found in other wines. Wines obtained by skin contact with exogenous enzymes exhibited the most complex volatile composition with increased levels of many key monoterpenoids, alcohols and esters.

Influence of Grape Flesh on the Retention and Composition of Polyphenols from Skins and Seeds

This study examined the impact of grape flesh polysaccharide, protein, and amino acid contents on polyphenol retention from skins and seeds in Pinot noir (Vitis vinifera) and cold-hardy interspecific cultivars Marquette and Frontenac (Vitis spp.). After isolating grape tissues (skin, seed, and flesh), they were soaked either individually or combined with other tissues in a wine-like solution for up to 7 days. Findings revealed that flesh significantly reduces the concentration of condensed tannin, and mono- and diglucoside forms of anthocyanins in the supernatants, due to its rich content in polysaccharides and proteins. Frontenac skin and flesh tissues were the main sources of soluble proteins, amino acids, and soluble polysaccharides. Surprisingly, Marquette exhibited a higher retention of skin tannin than Pinot noir, likely due to its smaller tannin molecular mass, and a potential competitive effect with anthocyanins for the binding sites of flesh.

Chemically Modified Clay Adsorbents Used in the Retention of Protein and Polyphenolic Compounds from Sauvignon Blanc White Wine

During the manufacturing process of white wine, various physicochemical reactions can occur and can affect the quality of the finished product. For this reason, it is necessary to apply different treatments to minimize distinct factors such as protein instability and pinking phenomenon, which can affect the organoleptic properties of wines and their structure. In this work, a new method for the preparation of a sorbent-type material is presented through the fractional purification of native bentonite in three fractions (Na-BtF1, Na-BtF2, and Na-BtF3). Furthermore, the influence of the prepared sorbents on pH, conductivity, and amino nitrogen level was analyzed. The absorbents prepared and tested in wine solutions were characterized using the following physico-chemical methods: Brunauer-Emmett-Teller and Barrett-Joyner-Halenda (BET-BJH) method, X-ray diffraction (XRD) technique, and transform-coupled infrared spectroscopy Fourier with attenuated total reflection (FTIR-ATR). Following the analyses carried out on the retention of protein content and polyphenolic compounds, it was found that materials based on natural clay have suitable adsorption properties.

Mass Spectrometry-Based Proteomic Profiling of a Silvaner White Wine

The comprehensive identification of the proteome content from a white wine (cv. Silvaner) is described here for the first time. The wine protein composition isolated from a representative wine sample (250 L) was identified via mass spectrometry (MS)-based proteomics following in-solution and in-gel digestion methods after being submitted to size exclusion chromatographic (SEC) fractionation to gain a comprehensive insight into proteins that survive the vinification processes. In total, we identified 154 characterized (with described functional information) or so far uncharacterized proteins, mainly from Vitis vinifera L. and Saccharomyces cerevisiae. With the complementarity of the two-step purification, the digestion techniques and the high-resolution (HR)-MS analyses provided a high-score identification of proteins from low to high abundance. These proteins can be valuable for future authentication of wines by tracing proteins derived from a specific cultivar or winemaking process. The proteomics approach presented herein may also be generally helpful to understand which proteins are important for the organoleptic properties and stability of wines.

Use of potassium polyaspartate on white wines: interaction with proteins and aroma compounds

The precipitation of tartaric salts represents one of the main visual sensory faults of white wines. It can be prevented by cold stabilization or adding some adjuvants, such as potassium polyaspartate (KPA). KPA is a biopolymer that can limit the precipitation of tartaric salts linking the potassium cation, however, it could interact also with other compounds affecting wine quality. The present work aims to study the effect of potassium polyaspartate on proteins and aroma compounds of two white wines, at different storage temperatures (4 °C and 16 °C). The KPA addition showed positive effects on the quality of wines, with a significant decrease of unstable proteins (up to 92%), also related to better wine protein stability indices. A Logistic function well described the effect of KPA and storage temperature on protein concentration (R² > 0.93; NRMSD: 1.54-3.82%). Moreover, the KPA addition allowed the preservation of the aroma concentration and no adversely effects were pointed out. Alternatively to common enological adjuvants, KPA could be considered a multifunctional product against tartaric and protein instability of white wines, avoiding adverse effects on their aroma profile.

Effect of Pre-Fermentative Bentonite Addition on Pinot Noir Wine Colour, Tannin, and Aroma Profile

Pinot noir is a grape variety with thin grape skin, which means the extraction of colour and polyphenols is more challenging than other red grape varieties. The aim of this study was to investigate the impact of protein removal by adding bentonite prior to fermentation on Pinot noir wine composition. Four treatments were conducted, including the control without bentonite addition and Pinot noir wines produced with the addition of three different types of bentonites before cold soaking. The juice and wine samples were analysed for pathogenesis-related proteins, tannin, wine colour parameters, and aroma composition. The results showed that bentonite addition at 0.5 g/L had little impact on tannin and aroma compounds but more impact on wine colour, especially significantly higher level of SO2 resistant pigments observed in Na bentonite addition treatment. This study indicates the potential use of bentonite to modulate the Pinot noir juice composition that may facilitate the extraction of colour components from grape into juice, which plays an important role in colour stabilization in finished wine.

Biomolecular Profiling by MALDI-TOF Mass Spectrometry in Food and Beverage Analyses

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has frequently been applied to the analysis of biomolecules. Its strength resides not only in compound identification but particularly in acquiring molecular profiles providing a high discriminating power. The main advantages include its speed, simplicity, versatility, minimum sample preparation needs, and a relatively high tolerance to salts. Other benefits are represented by the possibility of automation, high throughput, sensitivity, accuracy, and good reproducibility, allowing quantitative studies. This review deals with the prominent use of MALDI-TOF MS profiling in food and beverage analysis ranging from the simple detection of sample constituents to quantifications of marker compounds, quality control, and assessment of product authenticity. This review summarizes relevant discoveries that have been obtained with milk and milk products, edible oils, wine, beer, flour, meat, honey, and other alimentary products. Marker molecules are specified: proteins and peptides for milk, cheeses, flour, meat, wine and beer; triacylglycerols and phospholipids for oils; and low-molecular-weight metabolites for wine, beer and chocolate. Special attention is paid to sample preparation techniques and the combination of spectral profiling and statistical evaluation methods, which is powerful for the differentiation of samples and the sensitive detection of frauds and adulterations.

Quantification of protein by acid hydrolysis reveals higher than expected concentrations in red wines: Implications for wine tannin concentration and colloidal stability

Protein is reportedly negligible in most red wines, due to its loss following co-precipitation with phenolic substances. A method for protein quantification in red wine was developed which overcame analytical interference from phenolic substances, based on ethanol precipitation, followed by acid-hydrolysis and amino acid quantification. Protein concentration was surveyed in a range of red wines produced from V. vinifera and interspecific (Vitis spp) hybrids, revealing higher than expected concentrations, ranging from 23 mg/L ± 2.57 to 380 mg/L ± 16. The results showed that tannin extracted from grapes remains soluble in wine in the presence of protein even at high protein (>100 mg/L) and tannin (>500 mg/L) concentrations. As a further consequence of this, the particle size and concentration of colloids within high- and low-protein wines were similar, independent of protein or tannin concentration. Higher wine tannin concentration was also correlated with increased heat stability of wine protein.

Development of simple, scalable protease production from Botrytis cinerea

Abstract

Heat haze-forming proteins are stable during winemaking and are typically removed via adsorption to bentonite. Proteolytic degradation is an alternative method to prevent wine-haze and offers the opportunity to reduce the environmental impacts and labor cost of the process. Herein, we describe the development of a production system for Botrytis cinerea proteases for the enzymatic degradation of heat haze-forming proteins. The effect of culture medium on the secretion of glucan by B. cinerea was investigated and methods to inactivate B. cinerea laccase in liquid culture medium were assessed. Protease production by B. cinerea was scaled up from 50 mL in shake flasks to 1 L in bioreactors, resulting in an increase in protease yield from 0.30 to 3.04 g L⁻¹. Glucan secretion by B. cinerea was minimal in culture medium containing lactose as a carbon source and either lactic or sulfuric acid for pH control. B. cinerea laccases were inactivated by reducing the pH of culture supernatant to 1.5 for 1 h. B. cinerea proteases were concentrated and partially purified using ammonium sulfate precipitation. SWATH-MS identified aspartic acid protease BcAP8 amongst the precipitated proteins. These results demonstrate a simple, affordable, and scalable process to produce proteases from B. cinerea as a replacement for bentonite in winemaking.

Key points

• Isolates of B. cinerea that produce proteases with potential for reducing wine heat-haze forming proteins were identified.

• Media and fermentation optimization increased protease yield tenfold and reduced glucan secretion.

• Low pH treatment inactivated laccases but not proteases.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11817-1.

The Effect of Dicarboxymethyl Cellulose on the Prevention of Protein Haze Formation on White Wine

Wine clarity is a critical aspect in the commercialization of white wines. The formation of wine haze can be attributed to the aggregation and precipitation of heat-unstable wine proteins. Bentonite fining is the commonly used method in winemaking for protein removal, but it is responsible for loss of wine volume and quality. Dicarboxymethyl cellulose (DCMC) was developed as a potential alternative to bentonite. Water-insoluble DCMC was prepared via catalyzed heterogeneous etherification using sodium chloromalonate and potassium iodide. White wine fining trials were benchmarked with different dosages of DCMC against a bentonite. A high-performance liquid chromatography method was optimized for protein quantification. The samples underwent heat stability tests to evaluate wine turbidity before and after fining. Results show that DCMC successfully reduced the wine protein content and turbidity. DCMC produced heat-stable wines with dosages higher than 0.25 g/L. The innovative application of DCMC in the wine sector shows potential due to its ability to stabilize white wines while overcoming problems associated with bentonite, such as lees production and loss of wine, contributing to a more sustainable process.

Effect of Pre-Fermentative Maceration and Fining Agents on Protein Stability, Macromolecular, and Phenolic Composition of Albariño White Wines: Comparative Efficiency of Chitosan, k-Carrageenan and Bentonite as Heat Stabilisers

In this work, the effect of pre-fermentative skin maceration (PFSM) on the chemical composition of the macromolecular fraction, polysaccharides and proteins, phenolic compounds, chromatic characteristics, and protein stability of Albariño monovarietal white wines was studied. PFSM increased the extraction of phenolic compounds and polysaccharides and reduced the extraction of pathogenesis-related proteins (PRPs). PFSM wine showed significantly higher protein instability. Sodium and calcium bentonites were used for protein stabilisation of wines obtained with PFSM (+PFSM) and without PFSM (-PFSM), and their efficiencies compared to fungal chitosan (FCH) and k-carrageenan. k-Carrageenan reduced the content of PRPs and the protein instability in both wines, and it was more efficient than sodium and calcium bentonites. FCH was unable to heat stabilise both wines, and PRPs levels remained unaltered. On the other hand, FCH decreased the levels of wine polysaccharides by 60%. Sodium and calcium bentonite also decreased the levels of wine polysaccharides although to a lower extent (16% to 59%). k-Carrageenan did not affect the wine polysaccharide levels. Overall, k-carrageenan is suitable for white wine protein stabilisation, having a more desirable impact on the wine macromolecular fraction than the other fining agents, reducing the levels of the wine PRPs without impacting polysaccharide composition.

Moment of Bentonite Addition, Co-Addition of Tannins, and Bentonite Type Affect the Differential Affinity of Pathogenesis-Related Grape Proteins towards Bentonite during Fermentation

To test the effect of the moment of bentonite addition, co-addition of tannins, and bentonite type on the differential affinity of pathogenesis-related (PR) proteins towards bentonite during grape must fermentation, three separate experiments were set up. PR proteins in the obtained wines were analyzed by reverse phase and size exclusion high-performance liquid chromatography (HPLC). The most significant reduction of bentonite dose and PR protein concentration was achieved by applying bentonite in the last third of fermentation. Particular thaumatin-like proteins (TLP) and proteins with lower molecular mass in general were more affected than others, while TLPs were more affected than chitinases. Exogenous enological tannins interacted with particular PR proteins, mostly TLPs, and lowered the total bentonite dose required. The combined application of tannins and bentonite in fermentation removed more PR proteins than bentonite alone, but did not achieve a synergistic effect in reducing the bentonite dose. Various bentonite types, including two Na-activated bentonites, an activated Na bentonite with specifically adsorbed silica, and an active Na-Ca bentonite, exhibited differential affinity towards different PR proteins. The results obtained could be used in developing wine fining protocols which combine treatments with complementary affinity for adsorption and removal of PR proteins, and in this way achieve greater efficiency of bentonite fining by reducing its total dose, which is of significant interest to the wine industry.

Mass spectrometry of peptides and proteins using digestion by a grape cysteine protease at pH 3

Cysteine protease from grapevine (Vitis vinifera) belongs to those resistant proteins, which survive the process of vinification and can therefore be detected as wine components. Its amino acid sequence shows a homology to other members of the papain family, but the enzyme has only partially been explored so far. In order to get more biochemical information with the help of mass spectrometry (MS), wine proteins were collected by ultrafiltration and separated by gel permeation chromatography. The purified enzyme surprisingly displayed a high molecular mass value of around 200 kDa, indicating a possible oligomeric status and aggregation, as it entered only negligibly the separating 10% gel during polyacrylamide gel electrophoresis. The isoelectric point (pI) value of 3.6 was determined by chromatofocusing. Matrix-assisted laser desorption/ionization (MALDI)-MS was employed to evaluate the cleavage specificity and usefulness of the isolated cysteine protease in protein and peptide research. A potential applicability could be anticipated from the efficient digestion performance in volatile ammonium formate buffers at pH 3. Common peptides were digested and the resulting products analyzed by MS/MS sequencing. Then, mixtures of protein standards and extracted barley nuclear proteins were processed in the same way. Grape cysteine protease is nonspecific but shows a certain preference for Arg, Lys, and also Leu residues. Compared with papain, it seems not to require fully the presence of a large hydrophobic residue adjacent to that at the cleavage site. The enzyme is suitable for protein research as it produces peptides of a reasonable length in acidic pH.

White Wine Protein Instability: Mechanism, Quality Control and Technological Alternatives for Wine Stabilisation—An Overview

Wine protein instability depends on several factors, but wine grape proteins are the main haze factors, being mainly caused by pathogenesis-related proteins (thaumatin-like proteins and chitinases) with a molecular weight between 10~40 kDa and an isoelectric point below six. Wine protein stability tests are needed for the routine control of this wine instability, and to select the best technological approach to remove the unstable proteins. The heat test is the most used, with good correlation with the natural proteins’ precipitations and because high temperatures are the main protein instability factor after wine bottling. Many products and technological solutions have been studied in recent years; however, sodium bentonite is still the most efficient and used treatment to remove unstable proteins from white wines. This overview resumes and discusses the different aspects involved in wine protein instability, from the wine protein instability mechanisms, the protein stability tests used, and technological alternatives available to stabilise wines with protein instability problems.

Regeneration of Magnetic Nanoparticles Used in the Removal of Pathogenesis-Related Proteins from White Wines

Protein haze remains a serious problem for the wine industry and requires costly bentonite treatment, leading to significant wine volume loss. Recently developed magnetic separation technology that allows a fast and efficient separation of haze proteins from wine shows promise for the development of an alternative method for white wine fining. The key purpose of this study was to understand the potential of the nanoparticles to be reused in multiple fining and regeneration cycles. Bare and acrylic-acid-based plasma polymer coated magnetic nanoparticles were cleaned with water, 10% SDS/water and acetone/water solution after each adsorption cycle to investigate their restored efficiency in removing pathogenesis-related proteins from three unfined white wines. The concentrations of metals, acids and phenolics were monitored to determine changes in the concentration of these essential wine constituents. The regeneration study verified that the acrylic acid plasma-coated magnetic nanoparticles, which underwent ten successive adsorption-desorption processes, still retained close to the original removal capacity for haze proteins from wines when 10% SDS solution and water were used for surface regeneration. In addition, the concentrations of organic acids and wine phenolic content remained almost unchanged, which are important indicators for the retention of the original wine composition.

Mass spectrometry based proteomics for the molecular fingerprinting of Fiano, Greco and Falanghina cultivars

The official methodologies used for the identification and comparison of vine cultivars are ampelography and ampelometry. These methodologies are essentially based on qualitative assessments or biometric dependent morphological features of the plant. The heterogeneity of cultivars and consequently the increasing demand for a more detailed product typization, led to the introduction of new methodologies for the varietal characterization. In this scenario, proteomics has already proved to be a very useful discipline for the typization of many kinds of edible products. In this paper, we present a proteomic study carried out on three cultivars of Vitis vinifera peculiar of south Italy (Campania) used for white wine production (Fiano, Greco and Falanghina) by advanced biomolecular mass spectrometry approach. Our data highlight variations in the proteomic profiles during ripening for each cultivar and between analyzed cultivars, thus suggesting a new way to outline the biomolecular signature of vines.

High-proline proteins in experimental hazy white wine produced from partially botrytized grapes

Undesirable effects of the pathogen Botrytis cinerea include reduced quality and quantity of wine grapes. Winemaking is also complicated by the formation of a protein haze in white wines and oxidative browning of red wines. We analyzed proteins in experimental Moravian white wines characterized by their instability and haze formation in bottles during storage despite prior bentonite treatment. To study the relationship of wine proteins and haze, we carried out proteomics on hazy and clear white wines produced with partly or largely botrytized grapes and standard reference wines. Wine proteins were identified after their extraction, electrophoresis, and tryptic digestion by reversed-phase liquid chromatography of peptides, coupled with tandem mass spectrometry. Plant defense proteins, yeast glycoproteins, and various enzymes from Botrytis, particularly hydrolases, were found. As the content of the known haze-active thaumatin-like proteins and chitinases was visually low on stained gels (missing bands) compared to previous studies with unfined wines, other proteins are discussed in terms of the haze formation. As the main novelty, this work reveals the role of high proline-containing proteins in the propensity of white wines to turbidity following prior Botrytis damage of grapes.

Chitinases and thaumatin-like proteins in Sauvignon Blanc and Chardonnay musts during alcoholic fermentation

Protein precipitation, also referred to as protein instability, may lead to haziness in bottled wines and result in significant commercial losses. To avoid problems of this nature, fining finished wines with clay (bentonite) is the most commonly applied methodology. However, bentonite fining reduces yield and may affect wine quality. Protein haze has been primarily linked to grape pathogenesis-related proteins, in particular chitinases and thaumatin-like proteins. To better understand the persistence of these proteins during fermentation, reverse phase chromatography was used to monitor the evolution of total grape proteins as well as of chitinases and thaumatin-like proteins during alcoholic fermentation. The data confirm a previously reported significant decrease in total protein content during fermentation. This reduction in total protein levels was observed throughout fermentation, and was affected by factors such as fermentation temperature, yeast strain or grape cultivar. However, significant changes in the concentration of free chitinases were observed in a yeast strain-dependent manner. The data thus confirm the correlation between the levels of yeast cell wall chitin and changes in chitinase concentration, and suggest that it is primarily the amount of lateral chitin, and not the chitin in bud scars, that is responsible for this activity.

Characterization of Endogenous Nanoparticles from Roasted Chicken Breasts

Emergence of endogenous nanoparticles in thermally processed food has aroused much attention due to their unique properties and potential biological impact. The aim of this study was to investigate the presence of fluorescence nanoparticles in roasted chicken breasts, elemental composition, physicochemical properties, and their molecular interaction with human serum albumin (HSA). Transmission electron microscopy analysis revealed that the foodborne nanoparticles from roasted chicken were nearly spherical with an average particle size of 1.7 ± 0.4 nm. The elemental analysis of X-ray photoelectron spectroscopy showed the composition of nanoparticles as 47.4% C, 25.8% O, and 26.1% N. The fluorescence of HSA was quenched by the nanoparticles following a static mode, and the molecular interaction of nanoparticles with HSA was spontaneous (Δ G⁰ < 0), where hydrogen bonding and van der Waals forces played an important role during HSA-nanoparticles complex stabilization through thermodynamic analysis by isothermal titration calorimetry. The principal location of the nanoparticles binding site on HSA was primarily in site I as determined by site-specific marker competition. The conformational of HSA was also changed and α-helical structure decreased in the presence of nanoparticles. Our studies revealed that fluorescent nanoparticles were produced after roasting of chicken breast at 230 °C for 30 min for the first time. The obtained nanoparticles can interact with HSA in a spontaneous manner, thus providing valuable insight into foodborne NPs as well as their effects to human albumin protein.

Extraction of Pathogenesis-Related Proteins and Phenolics in Sauvignon Blanc as Affected by Grape Harvesting and Processing Conditions

Thaumatin-like proteins (TLPs) and chitinases are the two main groups of pathogenesis-related (PR) proteins found in wine that cause protein haze formation. Previous studies have found that phenolics are also involved in protein haze formation. In this study, Sauvignon Blanc grapes were harvested and processed in two vintages (2011 and 2012) by three different treatments: (1) hand harvesting with whole bunch press (H-WB); (2) hand harvesting with destem/crush and 3 h skin contact (H-DC-3); and (3) machine harvesting with destem/crush and 3 h skin contact (M-DC-3). The juices were collected at three pressure levels (0.4 MPa, 0.8 MPa and 1.6 MPa), some juices were fermented in 750 mL of wine bottles to determine the bentonite requirement for the resulting wines. Results showed juices of M-DC-3 had significantly lower concentration of proteins, including PR proteins, compared to those of H-DC-3, likely due to the greater juice yield of M-DC-3 and interactions between proteins and phenolics. Juices from the 0.8–1.6 MPa pressure and resultant wines had the highest concentration of phenolics but the lowest concentration of TLPs. This supported the view that TLPs are released at low pressure as they are mainly present in grape pulp but additional extraction of phenolics largely present in skin occurs at higher pressing pressure. Wine protein stability tests showed a positive linear correlation between bentonite requirement and the concentration of chitinases, indicating the possibility of predicting bentonite requirement by quantification of chitinases. This study contributes to an improved understanding of extraction of haze-forming PR proteins and phenolics that can influence bentonite requirement for protein stabilization.

Comparative protein profile analysis of wines made from Botrytis cinerea infected and healthy grapes reveals a novel biomarker for gushing in sparkling wine

Fungal infection of grapes with the plant pathogenic fungus Botrytis (B.) cinerea was shown to cause a degradation of proteins in the resulting wine. Moreover, it influences the foaming properties of the wine. The aim of this study was to compare the protein composition in B. cinerea infected and healthy grapes and of wines produced from such grapes as well as to analyze whether the resulting changes in the protein profiles can be related the occurrence of gushing in sparkling wine. SDS-PAGE and reversed phase HPLC were applied to analyze the protein composition of healthy and botrytized grapes and of wines made from botrytized and healthy grapes. B. cinerea infection led to a general decrease of protein content in infected grapes and wines suggesting proteolytic activity of this fungus. Especially the concentration of a protein with a protein band at ~17kDa underwent a significant decrease in wine made from infected grapes. This protein was identified as Seripauperin 5 (PAU5) from Saccharomyces cerevisiae. A degradation of PAU5 and other proteins and the occurrence of a laccase from B. cinerea were observed in a gushing sparkling wine. Screening of sparkling wines showed that samples lacking PAU5 had a high probability for the occurrence of gushing. We suggest that the absence of protein PAU5 might be a useful biomarker for the occurrence of gushing in sparkling wine.

Proteomic Analysis of Sauvignon Blanc Grape Skin, Pulp and Seed and Relative Quantification of Pathogenesis-Related Proteins

Thaumatin-like proteins (TLPs) and chitinases are the main constituents of so-called protein hazes which can form in finished white wine and which is a great concern of winemakers. These soluble pathogenesis-related (PR) proteins are extracted from grape berries. However, their distribution in different grape tissues is not well documented. In this study, proteins were first separately extracted from the skin, pulp and seed of Sauvignon Blanc grapes, followed by trypsin digestion and analysis by liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS). Proteins identified included 75 proteins from Sauvignon Blanc grape skin, 63 from grape pulp and 35 from grape seed, mostly functionally classified as associated with metabolism and energy. Some were present exclusively in specific grape tissues; for example, proteins involved in photosynthesis were only detected in grape skin and proteins found in alcoholic fermentation were only detected in grape pulp. Moreover, proteins identified in grape seed were less diverse than those identified in grape skin and pulp. TLPs and chitinases were identified in both Sauvignon Blanc grape skin and pulp, but not in the seed. To relatively quantify the PR proteins, the protein extracts of grape tissues were seperated by HPLC first and then analysed by SDS-PAGE. The results showed that the protein fractions eluted at 9.3 min and 19.2 min under the chromatographic conditions of this study confirmed that these corresponded to TLPs and chitinases seperately. Thus, the relative quantification of TLPs and chitinases in protein extracts was carried out by comparing the area of corresponding peaks against the area of a thamautin standard. The results presented in this study clearly demonstrated the distribution of haze-forming PR proteins in grape berries, and the relative quantification of TLPs and chitinases could be applied in fast tracking of changes in PR proteins during grape growth and determination of PR proteins in berries at harvest.

Wine protein haze: mechanisms of formation and advances in prevention

Protein haze is an aesthetic problem in white wines that can be prevented by removing the grape proteins that have survived the winemaking process. The haze-forming proteins are grape pathogenesis-related proteins that are highly stable during winemaking, but some of them precipitate over time and with elevated temperatures. Protein removal is currently achieved by bentonite addition, an inefficient process that can lead to higher costs and quality losses in winemaking. The development of more efficient processes for protein removal and haze prevention requires understanding the mechanisms such as the main drivers of protein instability and the impacts of various wine matrix components on haze formation. This review covers recent developments in wine protein instability and removal and proposes a revised mechanism of protein haze formation.

Study of combined effect of proteins and bentonite fining on the wine aroma loss

The wine aroma loss as a consequence of treatments with bentonite is due to the occurrence of multiple interaction mechanisms. In addition to a direct effect of bentonite, the removal of aroma compounds bound to protein components adsorbed by the clay has been hypothesized but never demonstrated. We studied the effect of bentonite addition on total wine aroma compounds (extracted from Moscato wine) in a model solution in the absence and presence of total and purified (thaumatin-like proteins and chitinase) wine proteins. The results showed that in general bentonite alone has a low effect on the loss of terpenes but removed ethyl esters and fatty acids. The presence of wine proteins in the solution treated with bentonite tended to increase the loss of esters with the longest carbon chains (from ethyl octanoate to ethyl decanoate), and this was significant when the purified proteins were used. The results here reported suggest that hydrophobicity can be one of the driving forces involved in the interaction of aromas with both bentonite and proteins.

Characterization of a grape class IV chitinase

A chitinase was purified from Vitis vinifera Manzoni Bianco grape juice and characterized. On the basis of proteomic analysis of tryptic peptides, a significant match identified the enzyme as a type IV grape chitinase previously found in juices of other V. vinifera varieties. The optimal pH and temperature for activity toward colloidal chitin were found to be 6 and 30 °C, respectively. The enzyme was found to hydrolyze chitin and oligomers of N-acetylglucosamine, generating N,N'-diacetylchitobiose and N-acetylglucosamine as products, but was inactive toward N,N'-diacetylchitobiose. The enzyme exhibited both endo- and exochitinase activities. Because yeast contains a small amount of chitin in the cell wall, the possibility of growth inhibition was tested. At a concentration and pH expected in ripe grapes, no inhibition of wine yeast growth by the chitinase was observed.

It's time to pop a cork on champagne's proteome!

Champagne is a world-renowned French sparkling wine, which undergoes many steps (fermentation, aging …) for its elaboration. Various compounds might evolve during this winemaking process and thus modify its final quality. Here, we report the first proteome analysis of two standard commercial Champagne wines, using the powerful Combinatorial Peptide Ligand Library (CPLL) technique. Indeed, wine proteins are present in small amounts but they are key compounds, likely to impact on both foam quality and aroma behavior. Forty-three unique gene products were retrieved in a single-varietal champagne and a blended champagne. Several proteins from Vitis vinifera together with seven yeast proteins were undoubtedly identified in these Champagne wines.

BIOLOGICAL SIGNIFICANCE

The main advantage of CPLLs was the detection of low abundance proteins despite the absence of purification or pre-concentration step. It is an important fact to take into account, since Champagne wines generally contain a low amount of proteins (5-10mg/L) that implies to usually concentrate wine proteins before 1D or 2D electrophoresis. Most Champagne proteins are grape and yeast glycoproteins which are considered as good foam "promoters". Some of these proteins might also interact with wine aromas, and thus contribute to the overall quality of Champagne wines. This article is part of a Special Issue entitled: Proteomics of non-model organisms.

Absence of fks1p in lager brewing yeast results in aberrant cell wall composition and improved beer flavor stability

The flavor stability during storage is very important to the freshness and shelf life of beer. However, beer fermented with a yeast strain which is prone to autolyze will significantly affect the flavor of product. In this study, the gene encoding β-1,3-glucan synthetase catalytic subunit (fks1) of the lager yeast was destroyed via self-clone strategy. β-1,3-glucan is the principle cell wall component, so fks1 disruption caused a decrease in β-1,3-glucan level and increase in chitin level in cell wall, resulting in the increased cell wall thickness. Comparing with wild-type strain, the mutant strain had 39.9 and 63.41 % less leakage of octanoic acid and decanoic acid which would significantly affect the flavor of beer during storage. Moreover, the results of European Brewery Convention tube fermentation test showed that the genetic manipulation to the industrial brewing yeast helped with the anti-staling ability, rather than affecting the fermentation ability. The thiobarbituric acid value reduced by 65.59 %, and the resistant staling value increased by 26.56 %. Moreover, the anti-staling index of the beer fermented with mutant strain increased by 2.64-fold than that from wild-type strain respectively. China has the most production and consumption of beer around the world, so the quality of beer has a significant impact on Chinese beer industry. The result of this study could help with the improvement of the quality of beer in China as well as around the world.

Effects of high hydrostatic pressure (HHP) on the protein structure and thermal stability of Sauvignon blanc wine

Protein haze development in bottled white wines is attributed to the slow denaturation of unstable proteins, which results in their aggregation and flocculation. These protein fractions can be removed by using bentonite; however, a disadvantage of this technique is its cost. The effects of high hydrostatic pressure (HHP) on wine stability were studied. Fourier transform infrared spectroscopy experiments were performed to analyse the secondary structure of protein, thermal stability was evaluated with differential scanning calorimetry, while a heat test was performed to determine wine protein thermal stability. The results confirmed that high pressure treatments modified the α-helical and β-sheet structures of wine proteins. Throughout the 60 days storage period the α-helix structure in HHP samples decreased. Structural changes by HHP (450 MPa for 3 and 5 min) improve thermal stability of wine proteins and thus delay haze formation in wine during storage.

Precipitation of champagne base wine proteins prior to 2D electrophoresis

Numerous methods have been employed to depict the protein content of wines. Among them, two-dimensional electrophoresis (2D-E) presents a powerful resolution, but has been poorly applied to wine. Furthermore, 2D-E was coupled with various extraction methods of proteins without any reference method for wine. Here, we describe a rapid method to extract proteins from a champagne base wine through ultrafiltration followed by precipitation with ethanol and trichloroacetic acid. More than 50 spots were visualized on 2D-gels (7 cm, pH 3-6) by colloidal Coomassie Brilliant Blue staining.

Aspartic acid protease from Botrytis cinerea removes haze-forming proteins during white winemaking

White wines suffer from heat-induced protein hazes during transport and storage unless the proteins are removed prior to bottling. Bentonite fining is by far the most commonly used method, but it is inefficient and creates several other process challenges. An alternative to bentonite is the enzymatic removal of haze-forming grape pathogenesis-related proteins using added proteases. The major problem with this approach is that grape pathogenesis-related proteins are highly protease resistant unless they are heat denatured in combination with enzymatic treatment. This paper demonstrates that the protease BcAP8, from the grape fungal pathogen Botrytis cinerea , is capable of degrading chitinase, a major class of haze-forming proteins, without heat denaturation. Because BcAP8 effectively removes haze-forming proteins under normal winemaking conditions, it could potentially benefit winemakers by reducing bentonite requirements.

White wine proteins: how does the pH affect their conformation at room temperature?

Our studies focused on the determination of aggregation mechanisms of proteins occurring in wine at room temperature. Even if the wine pH range is narrow (2.8 to 3.7), some proteins are affected by this parameter. At low pH, the formation of aggregates and the development of a haze due to proteins sometimes occur. The objective of this work was to determine if the pH impacted the conformational stability of wine proteins. Different techniques were used: circular dichroism and fluorescence spectroscopy to investigate the modification of their secondary and tertiary structure and also SAXS to determine their global shape. Four pure proteins were used, two considered to be stable (invertase and thaumatin-like proteins) and two considered to be unstable (two chitinase isoforms). Two pH values were tested to emphasize their behavior (pH 2.5 and 4.0). The present work highlighted the fact that the conformational stability of some wine proteins (chitinases) was impacted by partial modifications, related to the exposure of some hydrophobic sites. These modifications were enough to destabilize the native state of the protein. These modifications were not observed on wine proteins determined to be stable (invertase and thaumatin-like proteins).

Identification and partial characterization of extracellular aspartic protease genes from Metschnikowia pulcherrima IWBT Y1123 and Candida apicola IWBT Y1384

The extracellular acid proteases of non-Saccharomyces wine yeasts may fulfill a number of roles in winemaking, which include increasing the available nitrogen sources for the growth of fermentative microbes, affecting the aroma profile of the wine, and potentially reducing protein haze formation. These proteases, however, remain poorly characterized, especially at genetic level. In this study, two extracellular aspartic protease-encoding genes were identified and sequenced, from two yeast species of enological origin: one gene from Metschnikowia pulcherrima IWBT Y1123, named MpAPr1, and the other gene from Candida apicola IWBT Y1384, named CaAPr1. In silico analysis of these two genes revealed a number of features peculiar to aspartic protease genes, and both the MpAPr1 and CaAPr1 putative proteins showed homology to proteases of yeast genera. Heterologous expression of MpAPr1 in Saccharomyces cerevisiae YHUM272 confirmed that it encodes an aspartic protease. MpAPr1 production, which was shown to be constitutive, and secretion were confirmed in the presence of bovine serum albumin (BSA), casein, and grape juice proteins. The MpAPr1 gene was found to be present in 12 other M. pulcherrima strains; however, plate assays revealed that the intensity of protease activity was strain dependent and unrelated to the gene sequence.

Evidence for an extracellular acid proteolytic activity secreted by living cells of Saccharomyces cerevisiae PlR1: impact on grape proteins

In this work, Saccharomyces cerevisiae PlR1, a strain isolated from Pinot noir grapes in the Champagne area, was shown to secrete an acid proteolytic activity against bovine serum albumin. This proteolytic activity was detectable in cell-free culture supernatants at the beginning of the exponential growth phase and increased with yeast growth. Using a zymography method, only one protease band with a molecular mass of 72 kDa was observed. This extracellular proteolytic activity was detected in the pH range from 2 to 4 with a maximal value at pH 2.5 and 38 °C and was completely inhibited by pepstatin A. The secretion of this protease did not need any protein inducer and seemed to be insensitive to nitrogen catabolic repression. S. cerevisiae PlR1 was also able to secrete this proteolytic activity during alcoholic fermentation, and it was found to be active against grape proteins, with a molecular mass around 25 kDa, at optimal conditions of 38 °C, pH 3.5.

Quantification of chitinase and thaumatin-like proteins in grape juices and wines

Chitinases and thaumatin-like proteins are important grape proteins as they have a great influence on wine quality. The quantification of these proteins in grape juices and wines, along with their purification, is therefore crucial to study their intrinsic characteristics and the exact role they play in wines. The main isoforms of these two proteins from Chardonnay grape juice were thus purified by liquid chromatography. Two fast protein liquid chromatography (FLPC) steps allowed the fractionation and purification of the juice proteins, using cation exchange and hydrophobic interaction media. A further high-performance liquid chromatography (HPLC) step was used to achieve higher purity levels. Fraction assessment was achieved by mass spectrometry. Fraction purity was determined by HPLC to detect the presence of protein contaminants, and by nuclear magnetic resonance (NMR) spectroscopy to detect the presence of organic contaminants. Once pure fractions of lyophilized chitinase and thaumatin-like protein were obtained, ultra-HPLC (UHPLC) and enzyme-linked immunosorbent assay (ELISA) calibration curves were constructed. The quantification of these proteins in different grape juice and wine samples was thus achieved for the first time with both techniques through comparison with the purified protein calibration curve. UHPLC and ELISA showed very consistent results (less than 16% deviation for both proteins) and either could be considered to provide an accurate and reliable quantification of proteins in the oenology field.

Effects of ionic strength and sulfate upon thermal aggregation of grape chitinases and thaumatin-like proteins in a model system

Consumers expect white wines to be clear. During the storage of wines, grape proteins can aggregate to form haze. These proteins, particularly chitinases and thaumatin-like proteins (TL-proteins), need to be removed, and this is done through adsorption by bentonite, an effective but inefficient wine-processing step. Alternative processes are sought, but, for them to be successful, an in-depth understanding of the causes of protein hazing is required. This study investigated the role played by ionic strength (I) and sulfate toward the aggregation of TL-proteins and chitinases upon heating. Purified proteins were dissolved in model wine and analyzed by dynamic light scattering (DLS). The effect of I on protein aggregation was investigated within the range from 2 to 500 mM/L. For chitinases, aggregation occurred during heating with I values of 100 and 500 mM/L, depending on the isoform. This aggregation immediately led to the formation of large particles (3 μm, visible haze after cooling). TL-protein aggregation was observed only with I of 500 mM/L; it mainly developed during cooling and led to the formation of finite aggregates (400 nm) that remained invisible. With sulfate in the medium chitinases formed visible haze immediately when heat was applied, whereas TL-proteins aggregated during cooling but not into particles large enough to be visible to the naked eye. The data show that the aggregation mechanisms of TL-proteins and chitinases are different and are influenced by the ionic strength and ionic content of the model wine. Under the conditions used in this study, chitinases were more prone to precipitate and form haze than TL-proteins.

Roles of grape thaumatin-like protein and chitinase in white wine haze formation

Grape chitinase was found to be the primary cause of heat-induced haze formation in white wines. Chitinase was the dominant protein in a haze induced by treating Sauvignon blanc wine at 30 °C for 22 h. In artificial wines and real wines, chitinase concentration was directly correlated to the turbidity of heat-induced haze formation (50 °C for 3 h). Sulfate was confirmed to have a role in haze formation, likely by converting soluble aggregates into larger visible haze particles. Thaumatin-like protein was detected in the insoluble fraction by SDS-PAGE analysis but had no measurable impact on turbidity. Differential scanning calorimetry demonstrated that the complex mixture of molecules in wine plays a role in thermal instability of wine proteins and contributes additional complexity to the wine haze phenomenon.

Protein aggregation in white wines: influence of the temperature on aggregation kinetics and mechanisms

High temperatures (typically 80 °C) are widely used to assess wine stability with regard to protein haze or to study mechanisms involved in their formation. Dynamic light scattering experiments were performed to follow aggregation kinetics and aggregate characteristics in white wines at different temperatures (30-70 °C). Aggregation was followed during heating and cooling to 25 °C. Results were coupled with the study of the time-temperature dependence of heat-induced protein aggregation. At low temperature (40 °C), aggregation developed during heating. Colloidal equilibria were such that attractive interactions between species led to the rapid formation of micrometer-sized aggregates. At higher temperatures (60 and 70 °C), enhanced protein precipitation was expected and observed. However, high temperatures prevented aggregation, which mainly developed during cooling. Depending on the wine, cooling induced the formation of sub-micronic metastable aggregates stabilized by electrostatic repulsions, or the rapid formation of micrometer-sized aggregates, prone to sedimentation.