Food Forensics: Using Mass Spectrometry To Detect Foodborne Protein Contaminants, as Exemplified by Shiga Toxin Variants and Prion Strains

A colorimetric and SERS dual-mode aptasensor for the detection of Shiga toxin type II based on Mn/Fe-MIL(53)@AuNSs

Shiga toxin type II (Stx2), the major virulence component of enterohemorrhagic Escherichia coli, is strongly associated with the life-threatening hemolytic uremic syndrome thus posing a substantial risk to food safety and human health. In this work, a dual-mode aptasensor with colorimetric and surface-enhanced Raman scattering was developed for Stx2 specific detection based on noble metal nanoparticles and Raman reporter loaded metal-organic framework (Mn/Fe-MIL(53)@AuNSs-MBA). The Mn/Fe-MIL(53)@AuNSs could catalyze the H2O2-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), thereby enabling visual detection. Meanwhile, the SERS signal from MBA can be enhanced by the decorated AuNSs. Under optimal conditions, a linear range of 0.05-500 ng/mL with limit of detection (LOD) of 26 pg/mL was achieved in colorimetric mode and a linear range of 5-1000 ng/mL with LOD of 0.82 ng/mL in SERS mode, in which the dual-mode results complement each other, widening the linear range, increasing the accuracy and reliability of the detection. The method was further applied to the detection of Stx2 in milk with average recovery of 101.1 %, demonstrating its superior potential for bacterial toxin monitoring.

Recent Advances in the Detection of Food Toxins Using Mass Spectrometry

Edibles are the only source of nutrients and energy for humans. However, ingredients of edibles have undergone many physicochemical changes during preparation and storage. Aging, hydrolysis, oxidation, and rancidity are some of the major changes that not only change the native flavor, texture, and taste of food but also destroy the nutritive value and jeopardize public health. The major reasons for the production of harmful metabolites, chemicals, and toxins are poor processing, inappropriate storage, and microbial spoilage, which are lethal to consumers. In addition, the emergence of new pollutants has intensified the need for advanced and rapid food analysis techniques to detect such toxins. The issue with the detection of toxins in food samples is the nonvolatile nature and absence of detectable chromophores; hence, normal conventional techniques need additional derivatization. Mass spectrometry (MS) offers high sensitivity, selectivity, and capability to handle complex mixtures, making it an ideal analytical technique for the identification and quantification of food toxins. Recent technological advancements, such as high-resolution MS and tandem mass spectrometry (MS/MS), have significantly improved sensitivity, enabling the detection of food toxins at ultralow levels. Moreover, the emergence of ambient ionization techniques has facilitated rapid in situ analysis of samples with lower time and resources. Despite numerous advantages, the widespread adoption of MS in routine food safety monitoring faces certain challenges such as instrument cost, complexity, data analysis, and standardization of methods. Nevertheless, the continuous advancements in MS-technology and its integration with complementary techniques hold promising prospects for revolutionizing food safety monitoring. This review discusses the application of MS in detecting various food toxins including mycotoxins, marine biotoxins, and plant-derived toxins. It also explores the implementation of untargeted approaches, such as metabolomics and proteomics, for the discovery of novel and emerging food toxins, enhancing our understanding of potential hazards in the food supply chain.

Fluorescence spectroscopy and multispectral imaging for fingerprinting of aflatoxin-B1 contaminated (Zea mays L.) seeds: a preliminary study

Cereal seeds safety may be compromised by the presence of toxic contaminants, such as aflatoxins. Besides being carcinogenic, they have other adverse health effects on humans and animals. In this preliminary study, we used two non-invasive optical techniques, optical fiber fluorescence spectroscopy and multispectral imaging (MSI), for discrimination of maize seeds naturally contaminated with aflatoxin B₁ (AFB₁) from the uncontaminated seeds. The AFB₁-contaminated seeds exhibited a red shift of the emission maximum position compared to the control samples. Using linear discrimination analysis to analyse fluorescence data, classification accuracy of 100% was obtained to discriminate uncontaminated and AFB₁-contaminated seeds. The MSI analysis combined with a normalized canonical discriminant analysis, provided spectral and spatial patterns of the analysed seeds. The AFB₁-contaminated seeds showed a 7.9 to 9.6-fold increase in the seed reflectance in the VIS region, and 10.4 and 12.2-fold increase in the NIR spectral region, compared with the uncontaminated seeds. Thus the MSI method classified successfully contaminated from uncontaminated seeds with high accuracy. The results may have an impact on development of spectroscopic non-invasive methods for detection of AFs presence in seeds, providing valuable information for the assessment of seed adulteration in the field of food forensics and food safety.

Time of Detection of Prions in the Brain by Nanoscale Liquid Chromatography Coupled to Tandem Mass Spectrometry Is Comparable to Animal Bioassay

Prions cause transmissible and inevitably fatal neurological diseases in agriculturally important animals, including bovine spongiform encephalopathy in domestic cattle, scrapie in sheep and goats, and chronic wasting disease in cervids. Because animals are largely asymptomatic throughout the course of the disease, early detection of prion disease is important. Hamsters were peripherally (ip) inoculated with hamster-adapted (Sc237) prions. By week 13 of a 14-week disease course, clinical signs appeared. A multiple-reaction-monitoring-based method was used to quantitate the amount of proteinase-K-digested prions (PrP 27-30) and the extent of methionine 213 oxidation present in the brains of infected hamsters. Detectable amounts of PrP 27-30 were present in all animals after 4 weeks. The extent of methionine 213 oxidation decreased over time. When we compared our quantitation results to those from other researchers using bioassay, we observed that consistent detection of PrP 27-30 by mass spectrometry occurs at a time when prions are reliably detected by bioassay.

Shotgun Proteomics for Food Microorganism Detection

Classical and culture-based methods for the identification and characterization of the biochemical properties of microorganisms are slow and labor-intensive. Liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) has been used for the analysis of bacterial pathogen strain-specific diagnostic peptides allowing the characterization of bacterial strains.Here, we describe the analysis of tryptic digestion peptides by LC-ESI-MS/MS to search for specific biomarkers useful for the rapid identification of, on the one hand, the bacterial species and, on the other hand, the physiological and biochemical characteristics such as the expression of virulence factors, including toxins, immune-modulatory factors, and exoenzymes.

Villa T, Barros-Velázquez J, Cañas B, Sánchez-Pérez A, Calo-Mata P, Carrera M. Staphylococcus aureus Exotoxins and Their Detection in the Dairy Industry and Mastitis

Staphylococcus aureus constitutes a major food-borne pathogen, as well as one of the main causative agents of mastitis in dairy ruminants. This pathogen can produce a variety of extracellular toxins; these include the shock syndrome toxin 1 (TSST-1), exfoliative toxins, staphylococcal enterotoxins (SE), hemolysins, and leukocidins. S. aureus expresses many virulence proteins, involved in evading the host defenses, hence facilitating microbial colonization of the mammary glands of the animals. In addition, S. aureus exotoxins play a role in the development of both skin infections and mastitis. Indeed, if these toxins remain in dairy products for human consumption, they can cause staphylococcal food poisoning (SFP) outbreaks. As a result, there is a need for procedures to identify the presence of exotoxins in human food, and the methods used must be fast, sensitive, reliable, and accurate. It is also essential to determine the best medical therapy for human patients suffering from S. aureus infections, as well as establishing the relevant veterinary treatment for infected ruminants, to avoid economic losses in the dairy industry. This review summarizes the role of S. aureus toxins in the development of mastitis in ruminants, their negative effects in the food and dairy industries, and the different methods used for the identification of these toxins in food destined for human consumption.

Using Nanospray Liquid Chromatography and Mass Spectrometry to Quantitate Shiga Toxin Production in Environmental Escherichia coli Recovered from a Major Produce Production Region in California

A set of 45 environmental strains of Shiga toxin producing Escherichia coli (STEC) from three California counties were analyzed for Shiga toxin production by nanospray liquid chromatography-mass spectrometry and Vero cell bioassay. The STEC in this set comprised six serotypes ((O113:H21, O121:H19, O157:H7, O6:H34, O177:H25, and O185:H7) each containing either the stx_2a or stx_2c operon. Six of the seven O113:H21 were found to contain two distinct stx_2a operons. Eight strains of O157:H7 possessed a stx_2c operon whose A subunit gene was interrupted by an insertion sequence (IS1203v). Shiga toxin production was induced by nutrient depletion and quantitated by mass spectrometry. The 37 strains produced Shiga toxins in a near 50-fold range (1.4-49 ng/mL). The IS-interrupted strains expressed low but measurable amounts of the B subunits (0.5-1.9 ng/mL). Another strain possessed an identical stx operon without an IS interruption and produced intact Stx2c (5.7 ng/mL).