Analysis of lysozyme in cheese by immunocapture mass spectrometry

Development of aptamer-based monolithic sorbent in paper devices for lysozyme extraction in foods

BACKGROUND

Lysozyme (Lyz) is a protein commonly used as a food preservative, but it can cause severe allergic reactions. Detecting trace amounts of Lyz in food is essential, requiring sensitive, reliable, and accessible analytical methods. Aptamers (Apts) are recognition ligands that can be integrated into paper-based devices to offer low-cost and effective platforms for Lyz detection. However, the Apt-paper hybridization as sorptive phase remains insufficiently explored.

RESULTS

In this work, an Apt-functionalized monolith was developed as an affinity sorbent for Lyz determination in foods using thin-film microextraction (TFME). For this purpose, a nitrocellulose piece was coated with a monolithic polymer based on 2-[(methacryloyloxy)ethyl]trimethylammonium chloride to immobilize Apt onto monolith's surface via adsorption. Subsequently, the prepared selective device was used to extract Lyz, evaluating several parameters affecting Lyz retention and elution. The selected conditions were a phosphate buffer at pH 6 for loading and 0.2 M glycine pH 2.0 for elution. The developed TFME method, combined with HPLC-DAD, was applied for the determination of trace Lyz in egg-free and egg-containing foods, achieving satisfactory recoveries (75-107 %), precision (RSD <6.1 %), and limit of detection (0.0085 μg mL-1). Additionally, the developed Apt-monolith@paper was affordable (<4.5 €/device), stable, and reusable up to 5 extraction cycles.

SIGNIFICANCE

This work presents, for the first time, an Apt-monolith@paper for Lyz extraction from food samples. This strategy paves the way for advancements in analyzing proteins or hazardous compounds in food, contributing to quality control and safety.

Quantifying allergenic proteins using antibody-based methods or liquid chromatography-mass spectrometry/mass spectrometry: A review about the influence of food matrix, extraction, and sample preparation

Accurate quantification of allergens in food is crucial for ensuring consumer safety. Pretreatment steps directly affect accuracy and efficiency of allergen quantification. We systematically reviewed the latest advances in pretreatment steps for antibody-based methods and liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) protein quantification methods in food. For antibody-based methods, the effects induced by food matrix like decreased allergen solubility, epitope masking, and nonspecific binding are of the upmost importance. To mitigate interference from the matrix, effective and proper extraction can be used to obtain the target allergens with a high protein concentration and necessary epitope exposure. Removal of interfering substances, extraction systems (buffers and additives), assistive technologies, and commercial kits were discussed. About LC-MS/MS quantification, the preparation of the target peptides is the crucial step that significantly affects the efficiency and results obtained from the MS detector. The advantages and limitations of each method for pre-purification, enzymatic digestion, and peptide desalting were compared. Additionally, the application characteristics of microfluidic-based pretreatment devices were illustrated to improve the convenience and efficiency of quantification. A promising research direction is the targeted development of pretreatment methods for complex food matrices, such as lipid-based and carbohydrate-based matrices.

Co-encapsulation of Shirazi thyme (Zataria multiflora) essential oil and nisin using caffeic acid grafted chitosan nanogel and the effect of this nanogel as a bio-preservative in Iranian white cheese

The current study aims to co-encapsulate Shirazi thyme (Zataria multiflora) essential oil (ZEO) and nisin into chitosan nanogel as an antimicrobial and antioxidant agent to enhance the shelf-life of cheese. Chitosan-caffeic acid (CS-CA) nanogel was produced to co-encapsulate Zataria multiflora essential oil and nisin. This nanogel was characterized by dynamic light scattering (DLS), Fourier Transform Infrared (FTIR) spectroscopic analysis, X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) images. The effect of free (TFZN) and encapsulated ZEO-nisin in chitosan nanogel (TCZN) on the chemical and microbiological properties of Iranian white cheese was assessed. The particle size, polydispersity index value (PDI), zeta potential, antioxidant activity, and encapsulation efficiency of the optimal chitosan-ZEO-nisin nanogel were 421.6 nm, 0.343, 34.0 mV, 71.06%-82.69%, and 41.3 ± 0.5%, 0.79 ± 0.06 mg/mL. respectively. FTIR and XRD approved ZEO and nisin entrapment within chitosan nanogel. The chitosan nanogel showed a highly porous surface with an irregular shape. The bioactive compounds of ZEO and nisin decreased the pH changes in cheese. On the 60th day of storage, the acidity of treated samples was significantly lower than that of control. Although the lowest anisidine index value was observed in samples treated with sodium nitrate (NaNO3) (TS), there was no significant difference between this sample and TCZN. The lowest microbial population was observed in TCZN and TS. After 60 days of ripening, Coliforms were not detected in the culture medium of TCZN and TS. The results can contribute to the development of a natural preservative with the potential for application in the dairy industry.

Graphene Oxide/Silver Nanoparticles Platforms for the Detection and Discrimination of Native and Fibrillar Lysozyme: A Combined QCM and SERS Approach

We propose a sensing platform based on graphene oxide/silver nanoparticles arrays (GO/AgNPs) for the detection and discrimination of the native and toxic fibrillar forms of an amyloid-prone protein, lysozyme, by means of a combination of Quartz Crystal Microbalance (QCM) and Surface Enhanced Raman Scattering (SERS) measurements. The GO/AgNPs layer system was obtained by Langmuir-Blodgett assembly of the silver nanoparticles followed by controlled adsorption of GO sheets on the AgNPs array. The adsorption of native and fibrillar lysozyme was followed by means of QCM, the measurements provided the kinetics and the mechanism of adsorption as a function of protein concentration as well as the mass and thickness of the adsorbed protein on both nanoplatforms. The morphology of the protein layer was characterized by Confocal Laser Scanning Microscopy experiments on Thioflavine T-stained samples. SERS experiments performed on arrays of bare AgNPs and of GO coated AgNP after native, or fibrillar, lysozyme adsorption allowed for the discrimination of the native form and toxic fibrillar structure of lysozyme. Results from combined QCM/SERS studies indicate a general construction paradigm for an efficient sensing platform with high selectivity and low detection limit for native and amyloid lysozyme.

Molecularly Imprinted Polyscopoletin for the Electrochemical Detection of the Chronic Disease Marker Lysozyme

Herein we report the electropolymerization of a scopoletin based molecularly imprinted polymer (MIP) for the detection of lysozyme (Lyz), an enzymatic marker of several diseases in mammalian species. Two different approaches have been used for the imprinting of lysozyme based, respectively, on the use of a monomer-template mixture and on the covalent immobilization of the enzyme prior to polymer synthesis. In the latter case, a multi-step protocol has been exploited with preliminary functionalization of gold electrode with amino groups, via 4-aminothiophenol, followed by reaction with glutaraldehyde, to provide a suitable linker for lysozyme. Each step of surface electrode modification has been followed by cyclic voltammetry and electrochemical impedance spectroscopy, which has been also employed to test the electrochemical responses of the developed MIP. The sensors show good selectivity to Lyz and detect the enzyme at concentrations up to 292 mg/L (20 μM), but with different performances, depending on the used imprinting approach. An imprinting factor equal to 7.1 and 2.5 and a limit of detection of 0.9 mg/L (62 nM) and 2.1 mg/L (141 nM) have been estimated for MIPs prepared with and without enzyme immobilization, respectively. Competitive rebinding experiment results show that this sensing material is selective for Lyz determination. Tests were performed using synthetic saliva to evaluate the potential application of the sensors in real matrices for clinical purposes.

An antifouling interface integrated with HRP-based amplification to achieve a highly sensitive electrochemical aptasensor for lysozyme detection

We report here a highly sensitive sandwich type electrochemical aptasensor for lysozyme (lys) detection by the integration of an antifouling interface with HRP-based signal amplification. The biosensing interface with antifouling ability is designed, consisting of a lys-binding aptamer (LBA), dithiothreitol (DTT) and mercaptohexanol (MCH). When lys is captured by the immobilized LBA due to the specific recognition of the aptamer, gold nanoparticles (AuNPs) functionalized with HRP and LBA (HRP-AuNP-LBA) are further conjugated to the surface-bound lys, forming a sandwich assay format. HRP catalyzes the chemical oxidation of hydroquinone (HQ) by hydrogen peroxide (H₂O₂) to produce benzoquinone (BQ) which results in a large electrochemical reduction signal of BQ. Therefore, this reduction signal measured by differential pulse voltammetry (DPV) is used to detect lys. The catalytic behavior of HRP toward the reaction between HQ and H₂O₂, together with the high loading of HRP on AuNPs, remarkably amplifies the signal. A linear relationship between the DPV response and the logarithm of lys concentration from 0.01 pg mL^-1 to 10⁵ pg mL^-1 with a detection limit of 0.003 pg mL^-1 (S/N = 3) is obtained. The proposed biosensing platform combines antifouling ability and signal amplification, resulting in high sensitivity, providing an effective way for ultrasensitive assay of protein biomarkers in complex media.

Ultrasensitive detection of lysozyme in droplet-based microfluidic devices

Lysozyme (LYS) is a bacteriolytic enzyme, available in secretions such as saliva, tears and human milk. LYS is an important defence molecule of the innate immune system, and its overexpression can be a consequence of diseases such as leukemia, kidney disease and sarcoidosis. This paper reports on a digital microfluidic-based approach that combines the gold nanoparticle-enhanced chemiluminescence with aptamer interaction to detect human lysozyme into droplets 20 nanoliters in volume. The described method allows identifying LYS with a 44.6 femtomolar limit of detection, using sample volume as low as 1μL and detection time in the range of 10min. We used luminol to generate the chemiluminescence and demonstrated that the compartmentalization of LYS in droplets also comprising gold nanoparticles provided enhanced luminescence. We functionalized the gold nanoparticles with a thiolated aptamer to achieve the required selectivity that allowed us to detect LYS in human serum.

Dicoumarol assisted synthesis of water dispersible gold nanoparticles for colorimetric sensing of cysteine and lysozyme in biofluids

A schematic representation of the mechanism for the colorimetric sensing of Cys and Lys using DIC–Au NPs as a probe.

Evaluation of the efficiency of enological procedures on lysozyme depletion in wine by an indirect ELISA method

Potential residues of the potent allergen lysozyme used as a microbial stabilizing agent in wine production might pose a serious health thread to susceptible individuals. Therefore, EU legislation requires the labeling of the allergenic agent, if it is present in the final product. To allow for product testing, an indirect ELISA method to be specifically used in wine analysis was developed and validated. Furthermore, trial wines treated with defined amounts of lysozyme were subjected to an array of different filtration and other enological processing regimes in order to evaluate their potential to deplete the allergen content of the wines. By these means, processing methods ought to be identified that can be integrated in a good manufacturing practice guideline to enable wine producers to utilize lysozyme in their cellars and still provide wines free of allergenic residues. However, among the enological procedures under scrutiny, only bentonite fining proved to be capable of significantly reducing the allergenic residues.

Different analytical approaches in assessing antibacterial activity and the purity of commercial lysozyme preparations for dairy application

Hen egg-white lysozyme (LSZ) is currently used in the food industry to limit the proliferation of lactic acid bacteria spoilage in the production of wine and beer, and to inhibit butyric acid fermentation in hard and extra hard cheeses (late blowing) caused by the outgrowth of clostridial spores. The aim of this work was to evaluate how the enzyme activity in commercial preparations correlates to the enzyme concentration and can be affected by the presence of process-related impurities. Different analytical approaches, including turbidimetric assay, SDS-PAGE and HPLC were used to analyse 17 commercial preparations of LSZ marketed in different countries. The HPLC method adopted by ISO allowed the true LSZ concentration to be determined with accuracy. The turbidimetric assay was the most suitable method to evaluate LSZ activity, whereas SDS-PAGE allowed the presence of other egg proteins, which are potential allergens, to be detected. The analytical results showed that the purity of commercially available enzyme preparations can vary significantly, and evidenced the effectiveness of combining different analytical approaches in this type of control.

Prevalence and stability of lysozyme in cheese

The use of the preservative and potential allergen hen egg white lysozyme in cheese production has to be declared. In the present study, an HPLC method with fluorescence detection (HPLC-FLD) was optimised and validated for the analysis of lysozyme in cheese. Lysozyme was detected in concentrations between 30.8 and 386.2mg/kg cheese in 30 out of 46 analysed commercial cheese samples. During cheese production and storage for 0-54weeks a lysozyme satellite peak (LSP) was detected, which totals up to 18% of the lysozyme content. Mass spectrometry and peptide mass fingerprint revealed that LSP possesses the same primary structure as lysozyme. Since disulphide scrambling could not be detected, LSP was assigned to a conformational isomer of lysozyme. As a consequence, LSP was included in the HPLC-FLD analysis of lysozymes in cheese.

Electrochemical immunosensor for casein based on gold nanoparticles and poly(L-Arginine)/multi-walled carbon nanotubes composite film functionalized interface

In this paper, a novel electrochemical immunosensor for the determination of casein based on gold nanoparticles and poly(L-Arginine)/multi-walled carbon nanotubes (P-L-Arg/MWCNTs) composite film was proposed. The P-L-Arg/MWCNTs composite film was used to modify glassy carbon electrode (GCE) to fabricate P-L-Arg/MWCNTs/GCE through electropolymerization of L-Arginine on MWCNTs/GCE. Gold nanoparticles were adsorbed on the modified electrode to immobilize the casein antibody and to construct the immunosensor. The stepwise assembly process of the immunosensor was characterized by cyclic voltammetry and differential pulse voltammetry. Results demonstrated that the peak currents of [Fe(CN)(6)](3-/4-) redox pair decreased due to the formation of antibody-antigen complex on the modified electrode. The optimization of the adsorption time of gold nanoparticles, the pH of supporting electrolyte and the incubation time were investigated in details. Under optimal conditions, the peak currents obtained by DPV decreased linearly with the increasing casein concentrations in the range from 1 × 10(-7) to 1 × 10(-5) g mL(-1) with a linear coefficiency of 0.993. This electrochemical immunoassay has a low detection limit of 5 × 10(-8) g mL(-1) and was successfully applied to the determination of casein in cheese samples.

Food applications of bacterial cell wall hydrolases

Bacterial cell wall hydrolases (BCWHs) display a remarkable structural and functional diversity that offers perspectives for novel food applications, reaching beyond those of the archetype BCWH and established biopreservative hen egg white lysozyme. Insights in BCWHs from bacteriophages to animals have provided concepts for tailoring BCWHs to target specific pathogens or spoilage bacteria, or, conversely, to expand their working range to Gram-negative bacteria. Genetically modified foods expressing BCWHs in situ showed successful, but face regulatory and ethical concerns. An interesting spin-off development is the use of cell wall binding domains of bacteriophage BCWHs for detection and removal of foodborne pathogens. Besides for improving food safety or stability, BCWHs may also find use as functional food ingredients with specific health effects.

Development and validation of an enzyme-linked immunosorbent assay (ELISA) for quantification of lysozyme in cheese

A competitive enzyme-linked immunosorbent assay (ELISA) was developed to quantify the amount of the preservative and potential allergen lysozyme in cheese using a commercially available monoclonal antibody against hen egg white lysozyme. The limit of detection for lysozyme in a cheese matrix amounted to 2.73 ng/mL, and the working range comprises 3.125-800 ng/mL. Intra- and interassay coefficients of variation were lower than 12%. Neither cross-reactivity with alpha-lactalbumin and human lysozyme nor unspecific interference with matrix components was observed. The recovery of lysozyme-spiked cheese ranged from 87.4 to 93.6% at four concentrations (50, 100, 200, and 400 mg/kg). The ELISA method was also compared to a high-performance liquid chromatography (HPLC) method, confirming the reliability and accuracy of the ELISA. A total of 21 commercially available cheese samples produced with and without lysozyme were analyzed with ELISA as well as HPLC. Both methods showed good agreement with a correlation index of R2=0.990.