Analysis of commercial wines by LC-MS/MS reveals the presence of residual milk and egg white allergens

Food allergen detection by mass spectrometry: From common to novel protein ingredients

Food allergens are molecules, mainly proteins, that trigger immune responses in susceptible individuals upon consumption even when they would otherwise be harmless. Symptoms of a food allergy can range from mild to acute; this last effect is a severe and potentially life-threatening reaction. The European Union (EU) has identified 14 common food allergens, but new allergens are likely to emerge with constantly changing food habits. Mass spectrometry (MS) is a promising alternative to traditional antibody-based assays for quantifying multiple allergenic proteins in complex matrices with high sensitivity and selectivity. Here, the main allergenic proteins and the advantages and drawbacks of some MS acquisition protocols, such as multiple reaction monitoring (MRM) and data-dependent analysis (DDA) for identifying and quantifying common allergenic proteins in processed foodstuffs are summarized. Sections dedicated to novel foods like microalgae and insects as new sources of allergenic proteins are included, emphasizing the significance of establishing stable marker peptides and validated methods using database searches. The discussion involves the in-silico digestion of allergenic proteins, providing insights into their potential impact on immunogenicity. Finally, case studies focussing on microalgae highlight the value of MS as an effective analytical tool for ensuring regulatory compliance throughout the food control chain.

Determination of trace levels of organic fining agents in wines: Latest and relevant findings

The production of red wine plays a key role in the local and international economies of several nations. During the winemaking process, to clarify the final product, before bottling, and to remove undesired substances (proteins, phenols, and tannins), fining agents are commonly added to wines. These substances have different origins (animal and vegetable proteins or mineral compounds), and they show a potential risk for the health of allergic subjects. For these reasons, the residues of fining agents, constituted by exogenous proteins based on gluten, egg, and milk proteins, should not be present in the final product and their trace residues should be quantified with accuracy. In the last decade, several analytical approaches have been developed for their quantitative determination using different sample treatment protocols and analytical techniques. These methods are based on liquid chromatography coupled with mass spectrometry or enzyme-linked immunosorbent assays (ELISAs). Recently, biosensors have been proposed as a potential alternative to immunoassay approaches, allowing rapid, cheap, and simple multi-residue detection. This short review aimed to report the most recent and relevant findings in the field.

Determination of Tropomyosin in Shrimp and Crab by Liquid Chromatography–Tandem Mass Spectrometry Based on Immunoaffinity Purification

A UPLC-MS/MS method was developed for the detection of tropomyosin (TM) in shrimp and crab. After simple extraction, the samples were purified by immunoaffinity column and then digested by trypsin. The obtained sample was separated by Easy-nLC 1000-Q Exactive. The obtained spectrums were analyzed by Thermo Proteome Discoverer 1.4 software and then ANIQLVEK with high sensitivity was selected as the quantitative signature peptide. Isotope-labeled internal standard was used in the quantitative analysis. The method showed good linearity in the range of 5–5,000 μg/L with a limit of quantification (LOQ) of 0.1 mg/kg. The average recoveries were 77.22–95.66% with RSDs ≤ 9.97%, and the matrix effects were between 88.53 and 112.60%. This method could be used for rapid screening and quantitative analysis of TM in shrimp and crab. Thus, it could provide technical support for self-testing of TM by food manufacturers and promote further improvement of allergen labeling in China.

Selecting processing robust markers using high resolution mass spectrometry for the detection of milk in food products

BACKGROUND

Cow's milk allergy is one of the most reported food allergies in Europe. To help patients suffering from food allergies it is important to be able to detect milk in different foods. An analytical method that is gaining interest in the field of allergen detection is Ultra-High Performance Liquid Chromatography-tandem Mass Spectrometry, where the analyte is a target peptide. When these peptide biomarkers are selected the effect of food processing should be taken into account to allow a robust detection method.

OBJECTIVE

This works aims at identifying such processing stable peptide markers for milk for the Ultra-High Performance Liquid Chromatography-tandem Mass Spectrometry based detection of food allergens in different food products.

METHODS

Milk-incurred food materials that underwent several processing techniques were produced. This was followed by establishing tryptic peptide profiles from each matrix using Ultra-High Performance Liquid Chromatography-High Resolution Mass Spectrometry .

RESULT

A careful comparison of peptide profiles/intensities and the use of specific exclusion criteria resulted in the selection of 8 peptide biomarkers suitable for application in Ultra-High Performance Liquid Chromatography-tandem Mass Spectrometry based milk detection methods. One of these markers is a α-lactalbumin specific peptide, which has been determined to be stable in different incurred materials for the first time.

CONCLUSION

To our knowledge, this is the first systematic and experimentally based approach for the selection of suitable milk peptide biomarkers robust towards multiple, often applied food processing techniques for milk. Ensuring the exact knowledge of the food processing circumstances by starting from well-defined raw material and using fully controlled settings to produce incurred test material allowed the construction of a peptide database with robust markers. These robust markers can be used for the development of a robust detection method for milk in different food matrices.

Combination of polyvinylpolypyrrolidone extraction and standard addition strategy for the accurate determination of multiple allergen residues in red wine by UPLC-MS/MS

During the winemaking process, fining materials derived from milk and egg products are traditionally used to remove undesirable substances to reduce bitterness and astringency. The possible residues of allergens in treated wine may pose a potential risk for allergy patients. In this study, we developed a method for the simultaneous quantification of eight allergens (αS1-casein, αS2-casein, β-casein, κ-casein, β-lactoglobulin, lysozyme, ovalbumin and ovotransferrin) in red wine by ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS). The sample was extracted with polyvinylpolypyrrolidone (PVPP) solution, following trypsin digestion and peptide-level purification by solid-phase extraction (SPE). A strategy based on standard addition was used for the accurate quantification of the target allergens in wine products. The limits of detection (LODs) were shown to be 0.003-0.015 μg/mL for milk allergens and 0.1 μg/mL for egg allergens. This economical and reliable method would be appropriate for routine analysis and further allergen label management for red wine.

Selected Instrumental Techniques Applied in Food and Feed: Quality, Safety and Adulteration Analysis

This review presents an overall glance at selected instrumental analytical techniques and methods used in food analysis, focusing on their primary food science research applications. The methods described represent approaches that have already been developed or are currently being implemented in our laboratories. Some techniques are widespread and well known and hence we will focus only in very specific examples, whilst the relatively less common techniques applied in food science are covered in a wider fashion. We made a particular emphasis on the works published on this topic in the last five years. When appropriate, we referred the reader to specialized reports highlighting each technique's principle and focused on said technologies' applications in the food analysis field. Each example forwarded will consider the advantages and limitations of the application. Certain study cases will typify that several of the techniques mentioned are used simultaneously to resolve an issue, support novel data, or gather further information from the food sample.

Development of a sample preparation approach for the analysis of fining agents in wines by liquid chromatography with tandem mass spectrometry

During winemaking a wide variety of processing aids such as albumin, caseinates and lysozyme are often used. These proteins are considered allergenic and could become a human health risk in susceptible individuals. In our knowledge, there are no methods published for the analysis of these three proteins simultaneously by liquid chromatography with tandem mass spectrometry, with electrospray ionization. Therefore, in this work, a sample preparation approach for the analysis of α-casein, β-casein, albumin and lysozyme, in a single run, was performed and compared with published data. Through a pH adjustment, combining the use of cellulose ester membranes, a precipitation with organic solvents and a final concentration/clean-up, we achieved recovery values from 90.7 to 108.6%. The method was validated, showing determination coefficients R² ≥ 0.99. This method was able to quantify proteins even at lower levels (limits of quantification from 0.01 to 0.25 mg/L) than the current legal limits.

Multi-target detection of egg-white and pig gelatin fining agents in Nebbiolo-based aged red wine by means of nanoHPLC-HRMS

The presence of residues from fining agents in wines may represent a risk for allergic consumers and a source of discomfort for others, such as vegans. Even though ELISA is the official detection method for such residues, this technique may be hindered by cross-reactivity issues, or by matrix-molecule interference due to a high polyphenol content, especially in red wines. An HRMS-based method has been developed to detect pig gelatin and egg white in experimental five-year aged Nebbiolo-based red wine. Biomarker peptides were selected, after tryptic digestion, and quantified by multitarget nanoHPLC-HRMS analysis. The method resulted in an LLOQs of 5 µg/mL in the experimental wine, and between 1 and 2 µg/mL in the buffer. This method allowed both gelatin and egg white proteins to be detected and quantified in aged red wine, while whereas the commercial ELISA kit was instead unable to detect egg white in the same samples.

Are current analytical methods suitable to verify VITAL® 2.0/3.0 allergen reference doses for EU allergens in foods?

Food allergy affects up to 6% of Europeans. Allergen identification is important for the risk assessment and management of the inadvertent presence of allergens in foods. The VITAL® initiative for voluntary incidental trace allergen labeling suggests protein reference doses, based on clinical reactivity in food challenge studies, at or below which voluntary labelling is unnecessary. Here, we investigated if current analytical methodology could verify the published VITAL® 2.0 doses, that were available during this analysis, in serving sizes between 5 and 500 g. Available data on published and commercial ELISA, PCR and mass spectrometry methods, especially for the detection of peanuts, soy, hazelnut, wheat, cow's milk and hen's egg were reviewed in detail. Limit of detection, quantitative capability, matrix compatibility, and specificity were assessed. Implications by the recently published VITAL® 3.0 doses were also considered. We conclude that available analytical methods are capable of reasonably robust detection of peanut, soy, hazelnut and wheat allergens for levels at or below the VITAL® 2.0 and also 3.0 doses, with some methods even capable of achieving this in a large 500 g serving size. Cow's milk and hen's egg are more problematic, largely due to matrix/processing incompatibility. An unmet need remains for harmonized reporting units, available reference materials, and method ring-trials to enable validation and the provision of comparable measurement results.

Chemical hazards in grapes and wine, climate change and challenges to face

Climate change has an impact on the chemical risks associated to wine consumption related with grape development and microbial contamination. We can classify chemical hazards in wine into two groups: those present in grapes due to agricultural practices, environmental contamination or fungal growth and those coming from fermentation and the winemaking process. The first group includes mycotoxins, whilst the second encompasses ethyl carbamate, biogenic amines, sulfur dioxide and proteins used as technological ingredients such as fining material. Usually the effective control of chemical hazards is achieved by assuring that they either are minimized or absent in the final product since their removal is somewhat difficult and sometimes it may affect sensory properties, which is a major issue in wine. Interestingly, it is possible to give recommendations to avoid excess of these compounds, but more research is needed to face future challenges related to climate change and consumer demands.

Critical review on proteotypic peptide marker tracing for six allergenic ingredients in incurred foods by mass spectrometry

Peptide marker identification is one of the most important steps in the development of a mass spectrometry (MS) based method for allergen detection, since the robustness and sensitivity of the overall analytical method will strictly depend on the reliability of the proteotypic peptides tracing for each allergen. The European legislation in place issues the mandatory labelling of fourteen allergenic ingredients whenever used in different food formulations. Among these, six allergenic ingredients, namely milk, egg, peanut, soybean, hazelnut and almond, can be prioritized in light of their higher occurrence in food recalls for undeclared presence with serious risk decision. In this work, we described the results of a comprehensive evaluation of the current literature on MS-based allergen detection aiming at collecting all available information about proteins and peptide markers validated in independent studies for the six allergenic ingredients of interest. The main features of the targeted proteins were commented reviewing all details available about known isoforms and sequence homology particularly in plant-derived allergens. Several critical aspects affecting peptide markers reliability were discussed and according to this evaluation a final short-list of candidate markers was compiled likely to be standardized and implemented in MS methods for allergen analysis.

Wine Fining with Plant Proteins

Fining treatments involve the addition of a substance or a mixture to wine, and are generally carried out in order to clarify, stabilize or modify the wine’s organoleptic characteristics. Usually these fining agents will bind the target compound(s) to form insoluble aggregates that are subsequently removed from the wine. The main reasons to perform wine fining treatments are to carry out wine clarification, stabilization and to remove phenolic compounds imparting unwanted sensory characteristics on the wine, which is an operation that often relies on the use of animal proteins, such as casein, gelatin, egg and fish proteins. However, due to the allergenic potential of these animal proteins, there is an increasing interest in developing alternative solutions including the use of fining proteins extracted from plants (e.g., proteins from cereals, grape seeds, potatoes, legumes, etc.), and non-proteinaceous plant-based substances (e.g., cell wall polysaccharides and pomace materials). In this article, the state of the art alternative fining agents of plant origins are reviewed for the first time, including considerations of their organoleptic and technological effects on wine, and of the allergenic risks that they can pose for consumers.

An assessment of the impact of extraction and digestion protocols on multiplexed targeted protein quantification by mass spectrometry for egg and milk allergens

The unintentional presence of even trace amounts of certain foods constitutes a major hazard for those who suffer from food allergies. For many food industries, product and raw ingredient surveillance forms part of their risk assessment procedures. This may require the detection of multiple allergens in a wide variety of matrices. Mass spectrometry offers a possible solution for the quantification of multiple allergens in a single analysis. The capability of MS to quantify many peptides from a complex protein digestion is well known. However, a lack of matrix certified reference materials has made the optimisation of extraction and digestion conditions for multiplexed allergen quantification difficult to assess. Here, we report a systematic study, using preliminary screening followed by a Design of Experiments approach, to find the optimal buffer and digestion conditions for detecting milk and egg protein markers in a model processed food matrix. Five of the most commonly used buffers, two chaotropic reagents and two reducing reagents were assessed for the optimal extraction of multiple protein markers. While the choice of background buffer had little impact, the use of chaotropic and reducing reagents showed significant benefits for the extraction of most proteins. A full factorial design experiment was applied to the parameters shown to have a significant impact on protein recovery. These studies suggest that a single optimal set of extraction conditions enabling the quantitative recovery of all proteins is not easily achieved. Therefore, although MS is capable of the simultaneous quantification of many peptides in a single run, greater consideration of protein extraction is required before these are applied for multiplex allergen quantification in food matrices. Graphical abstract.

Analysis of allergenic residues in wines by triple quadrupole LCMS

During the winemaking are used technology coadjuvants, between them: albumin, caseinates and lysozyme. These compounds have great oenological properties, however, the presence of their residues can represent risks to people who are allergic to them because they are derived from eggs and milk. Mass spectrometry methods enables unambiguous determination of allergenic proteins at low levels in wines. Therefore, the aim of this study was to determine the concentrations of ovalbumin, alpha-casein, beta-casein and lysozyme in experimental wines treated with different concentrations of them by triple quadrupole liquid chromatography mass spectrometry with Jet Stream Electrospray Ionization (ESI). The wines were elaborated and treated with different concentrations of albumin, lysozyme and potassium caseinate. Bentonite and decantation were used for the removal of the fining agents. The quantification limits (LOQ) for ovalbumin, a-casein, b-casein and lysozyme were: 0.002 mg/L, 0.24 mg/L, 0.75 mg/L and 0.04 mg/L, respectively. Non residues of the proteins were identified in the experimental wines treated with the different amounts of potassium caseinate, albumin and lysozyme, analyzed in this study. These results provide an evidence of the absence of residues of caseinate, albumin and lysozyme in the concentrations tested in the wines if good treatment practices are followed.

Proteome Analysis of Urticating Setae From Thaumetopoea pityocampa (Lepidoptera: Notodontidae)

Thaumetopoea pityocampa (Denis & Schiffermüller) (Lepidoptera: Notodontidae) is harmful to conifer trees because of defoliation and to public health because of the release of urticating setae from the caterpillars. Contact with setae by humans and domestic animals induces dermatitis, usually localized to the exposed areas. Recent studies demonstrated the presence of a complex urticating mechanism where proteins present in the setae may play a role as activators of immune responses. Yet, limited information is available at present about the proteins occurring in the setae of T. pityocampa. Using a refined method for protein extraction from the setae, and a combination of liquid chromatography tandem-mass spectrometry (LC-MS/MS), de novo assembly of transcriptomic data, and sequence similarity searches, an extensive data set of 353 proteins was obtained. These were further categorized by molecular function, biological process, and cellular location. All the 353 proteins identified were found to match through BLAST search with at least one Lepidoptera sequence available in databases. We found the previously known allergens Tha p 1 and Tha p 2 described from T. pityocampa, as well as enzymes involved in chitin biosynthesis, one of the principal components of the setae, and serine proteases that were responsible for inflammatory and allergic reactions in other urticating Lepidoptera. This new proteomic database may allow for a better understanding of the complexity of allergenic reactions due to T. pityocampa and to other Lepidoptera sharing similar defense systems.

Hen egg white lysozyme is a hidden allergen in Italian commercial ciders

Hen egg white lysozyme (HEWL) is an enzyme used in alcoholic fermentation for its ability to control the growth of Gram-positive and spoilage bacteria, without inhibiting yeast growth, and it allows a reduction in the use of sulphur dioxide. Nevertheless, considering the potential allergenicity of this protein, the presence of HEWL should be declared on the label of the final product. In this work, we analysed 18 commercial Italian ciders by LC-MS/MS and found traces of HEWL in 12 samples without label declaration. We used Western blot and enzyme-linked immunosorbent assay (ELISA) to verify the immunological activity of HEWL, and to quantify its content in the ciders. Two out of 18 samples were found to be positive both by immunoblot and ELISA. The results indicate the requirement of a more stringent control of commercial ciders and the need of label declaration for ciders treated with such compounds.

Food allergen detection by mass spectrometry: the role of systems biology

Food allergy prevalence is rising worldwide, motivating the development of assays that can sensitively and reliably detect trace amounts of allergens in manufactured food. Mass spectrometry (MS) is a promising alternative to commonly employed antibody-based assays owing to its ability to quantify multiple proteins in complex matrices with high sensitivity. In this review, we discuss a targeted MS workflow for the quantitation of allergenic protein in food products that employs selected reaction monitoring (SRM). We highlight the aspects of SRM method development unique to allergen quantitation and identify opportunities for simplifying the process. One promising avenue identified through a comprehensive survey of published MS literature is the use of proteotypic peptides, which are peptides whose presence appears robust to variations in food matrix, sample preparation protocol, and MS instrumentation. We conclude that proteotypic peptides exist for a subset of allergenic milk, egg, and peanut proteins. For less studied allergens such as soy, wheat, fish, shellfish, and tree nuts, we offer guidance and tools for peptide selection and specificity verification as part of an interactive web database, the Allergen Peptide Browser (http://www.AllergenPeptideBrowser.org). With ongoing improvements in MS instrumentation, analysis software, and strategies for targeted quantitation, we expect an increasing role of MS as an analytical tool for ensuring regulatory compliance.

An SPR based sensor for allergens detection

A simple, sensitive and label-free optical sensor method was developed for allergens analysis using α-casein as the biomarker for cow's milk detection, to be used directly in final rinse samples of cleaning in place systems (CIP) of food manufacturers. A Surface Plasmon Resonance (SPR) sensor chip consisting of four sensing arrays enabling the measurement of samples and control binding events simultaneously on the sensor surface was employed in this work. SPR offers several advantages in terms of label free detection, real time measurements and superior sensitivity when compared to ELISA based techniques. The gold sensor chip was used to immobilise α-casein-polyclonal antibody using EDC/NHS coupling procedure. The performance of the assay and the sensor was first optimised and characterised in pure buffer conditions giving a detection limit of 58ngmL^-1 as a direct binding assay. The assay sensitivity can be further improved by using sandwich assay format and amplified with nanoparticles. However, at this stage this is not required as the detection limit achieved exceeded the required allergens detection levels of 2µgmL^-1 for α-S1-casein. The sensor demonstrated good selectivity towards the α-casein as the target analyte and adequate recoveries from CIP final rinse wash samples. The sensor would be useful tool for monitoring allergen levels after cleaning procedures, providing additional data that may better inform upon wider food allergen risk management decision(s) that are made by food manufacturer. In particular, this sensor could potentially help validate or optimise cleaning practices for a given food manufacturing process.

Implementation of an Enzyme Linked Immunosorbent Assay for the Quantification of Allergenic Egg Residues in Red Wines Using Commercially Available Antibodies

Since the early 2000s, labeling of potentially allergenic food components to protect people who suffer from food allergies is compulsory in numerous industrialized countries. In Europe, milk and egg components used during the winemaking process must be indicated on the label since July 1, 2012. Several ELISA procedures have been developed to detect allergenic residues in wines. However, the complexity of the wine matrix can inhibit the immunoenzymatic reaction. The aim of this study was to implement an ELISA assay for the detection of ovalbumin in red wines using commercially available antibodies. The specificity of the acquired antibodies and the absence of cross reactivity were assessed by immunoblotting and ELISA. An ELISA assay with a LOD of 14.2 μg/L and a LOQ of 56.4 μg/L of ovalbumin in aqueous solution was obtained. Differences in ELISA signals were observed when analyzing various fining agents, although reproducible conformation of the antigen could be reached for the comparison of ovalbumin and Ovicolle. The differences between samples in terms of pH could be leveled but the inhibition of the ELISA signal, positively correlated to the tannin content of the wines, could not be suppressed. Thus, standard curves of ovalbumin in several wines were obtained by relative quantification. The control steps and the difficulties encountered presented in this study should be considered by anybody working toward the development of ELISA assays for the detection of allergenic residues in complex food matrices.

Validation of a mass spectrometry-based method for milk traces detection in baked food

A simple validated LC-MS/MS-based method was set up to detect milk contamination in bakery products, taking the effects of food processing into account for the evaluation of allergen recovery and quantification. Incurred cookies were prepared at eight levels of milk contamination and were cooked to expose all milk components, including allergenic proteins, to food processing conditions. Remarkable results were obtained in term of sufficiently low LOD and LOQ (1.3 and 4 mg/kg cookies, respectively). Precision was calculated as intra-day repeatability (RSD in the 5-20% range) and inter-day repeatability (4 days; RSD never exceeded 12%). The extraction recovery values ranged from 20% to 26%. Method applicability was evaluated by analysing commercial cookies labelled either as "milk-free" or "may contain milk". Although the ELISA methodology is considered the gold standard for detecting allergens in foods, this robust LC-MS/MS approach should be a useful confirmatory method for assessing and certifying "milk-free" food products.

Allergenic proteins in enology: a review on technological applications and safety aspects

Proteinaceous products are widely used as fining agents during winemaking to remove unwanted insoluble particles and undissolved microscopic particles (colloidal material) from the must or wine to improve stability. Some of them (egg white, caseinates, and fish gelatine) have allergenic potential and the presence of their residues in the final product could represent a risk for allergic individuals. Moreover, lysozyme (an egg allergen) is included among wine additives to control the fermentation processes and avoid spoiling during winemaking. The aim of this paper is to review the experimental/clinical data on the use of allergenic products in enology and the measurement of relative risk for sensitized subjects. In addition, methods developed specifically for the quantification of allergenic residues in must and wine are described.

High precision mass measurements for wine metabolomics

An overview of the critical steps for the non-targeted Ultra-High Performance Liquid Chromatography coupled with Quadrupole Time-of-Flight Mass Spectrometry (UPLC-Q-ToF-MS) analysis of wine chemistry is given, ranging from the study design, data preprocessing and statistical analyses, to markers identification. UPLC-Q-ToF-MS data was enhanced by the alignment of exact mass data from FTICR-MS, and marker peaks were identified using UPLC-Q-ToF-MS(2). In combination with multivariate statistical tools and the annotation of peaks with metabolites from relevant databases, this analytical process provides a fine description of the chemical complexity of wines, as exemplified in the case of red (Pinot noir) and white (Chardonnay) wines from various geographic origins in Burgundy.

Next generation of food allergen quantification using mass spectrometric systems

Food allergies are increasing worldwide and becoming a public health concern. Food legislation requires detailed declarations of potential allergens in food products and therefore an increased capability to analyze for the presence of food allergens. Currently, antibody-based methods are mainly utilized to quantify allergens; however, these methods have several disadvantages. Recently, mass spectrometry (MS) techniques have been developed and applied to food allergen analysis. At present, 46 allergens from 11 different food sources have been characterized using different MS approaches and some specific signature peptides have been published. However, quantification of allergens using MS is not routinely employed. This review compares the different aspects of food allergen quantification using advanced MS techniques including multiple reaction monitoring. The latter provides low limits of quantification for multiple allergens in simple or complex food matrices, while being robust and reproducible. This review provides an overview of current approaches to analyze food allergens, with specific focus on MS systems and applications.

Development of a method for the quantification of caseinate traces in Italian commercial white wines based on liquid chromatography-electrospray ionization-ion trap-mass spectrometry

A method using the combination of size exclusion-solid phase extraction and ultrafiltration, followed by tryptic digestion and analysis of the protein digest by liquid chromatography-electrospray ionization-3D ion trap-mass spectrometry (LC-ESI-3D IT-MS), was developed for the detection and quantification of caseinate traces potentially resulting from fining processes in white wines. In particular, several tryptic peptides generated from the main proteins constituting caseinate (β-, αS1-, and αS2-caseins) were used as markers of its presence in the wine matrices; among them, the β-casein peptide GPFPIIV was found to be the best marker for quantification purposes. Method linearity and sensitivity were assessed on a series of Italian commercial white wines, first checked for the absence of any peptide signal attributable to caseins introduced during their production and subsequently spiked with increasing concentrations of caseinate, to provide samples for matrix-matched calibrations. Limits of detection ranging between 0.09 and 0.29 mg/L (S/N = 3), according to the wine, were achieved using a 10 mL sample volume and the MS signal of GPFPIIV as the response related to the caseinate concentration. Such levels are comparable or even lower than the one (0.25 mg/L) recently adopted as a threshold by European Union legislation concerning the indication of milk- and egg-derived fining agents on wine labels, that is, the most restrictive one among those currently proposed in the world.

Multi-allergen quantification of fining-related egg and milk proteins in white wines by high-resolution mass spectrometry

RATIONALE

A method based on High-Resolution Mass Spectrometry was developed for the simultaneous determination of fining agents containing potentially allergenic milk (casein) and egg-white (lysozyme and ovalbumin) proteins, added to commercial white wines at sub-ppm levels. Selected tryptic peptides were used as quantitative markers. An evaluation of protein digestion yields was also performed by implementing the (15)N-valine-labelled analogues of the best peptide markers identified for αS1 -casein and ovalbumin.

METHODS

The method was based on the combination of ultrafiltration (UF) of protein-containing wines, tryptic digestion of the dialyzed wine extracts and liquid chromatography/high resolution mass spectrometry (LC/HRMS) analysis of tryptic digests. Peptides providing the most intense electrospray ionization (ESI)-MS response were chosen as quantitative markers of the proteins under investigation.

RESULTS

Six-point calibrations were performed by adding caseinate and egg-white powder in the concentration range between 0.25 and 10 µg/mL, to an allergen-free white wine. The following three peptide markers, LTEWTSSNVMEER, GGLEPINFQTAADQAR and ELINSWVESQTNGIIR, were highlighted as best markers for ovalbumin, while GTDVQAWIR and NTDGSTDYGILQINSR for lysozyme and YLGYLEQLLR, GPFPIIV and FFVAPFPEVFGK for caseinate. Limits of detection (LODs) ranged from 0.4 to 1.1 µg/mL.

CONCLUSIONS

The developed method is suited for assessing the contemporary presence of allergenic milk and egg proteins characterizing egg white and caseinate, fining agents typically employed for wine clarification. The LODs of the method enable the detection of sub-ppm concentrations of residual fining agents, that could represent a potential risk for allergic consumers.