Advanced Mass Spectrometry for Food Safety and Quality (eBook)

MALDI─MS has a considerable impact on food safety and quality because it covers from proteomics to lipidomics [56], including polymer analysis [57] and, more recently, even low molecular weight analytes due to the introduction of matrix-less ionization techniques [e.g., desorption ionization on porous silicon (DIOS)] or new matrices such as ionic liquids, proton sponges, and metal nanoparticles. However, protein identification by peptide mass fingerprint still remains the main routine application [8]. This identification has played a relevant role in food chemistry especially in detection of food adulterations [30], characterization of safety, quality and food allergens, and investigation of protein structural modifications induced by various industrial processes that could be detrimental for food quality and safety [58–60]. Sample handling and pretreatment is a crucial step in these cases that can be very different depending on the physical state of the sample. Two major factors restricting the wider application of this technique have been throughput and cost per data point. Classic approaches are based on long, tedious, and expensive procedures (e.g., SDS gel electrophoresis separation followed by in-gel digestion). However, in recent years, novel molecular tools, the re-invention/re-application of mature technologies, and miniaturization of technology have both increased throughput and significantly reduced these costs (e.g., faster in-solution digestion of whole samples) [61–64]. Table 2 outlines a list of relevant applications recently published.

The capacity of MALDI-TOF-MS of identify proteins also offers a safe, cost-effective, and adaptable system for rapid identification of bacteria and fungi. Species differentiation of food pathogenic and spoilage bacteria is important to ensure food quality and safety. The growth of microbial contaminants in industrially produced beverages can cause turbidity, haze, and off-flavors resulting in quality loss often rendering the product undrinkable. MALDI-TOF-MS could deliver discriminative peptide mass fingerprints within minutes and could thus be a rapid and reliable tool for identification and differentiation [65]. To this end, different sample preparation methods ranging from plain cell smears to more elaborate extraction procedures including mechanical and enzymatic disruption of cells have been investigated [66,67]. Methods can be based on the analysis of whole bacterial cells that were suspended in an organic solvent or applied directly to the sample target. In a different sample preparation technique, cell extracts were obtained from intact bacterial cells by a dissolution/centrifugation step. The protocol applied for the study of cell extracts was shown to be very fast and simple, allowing the standardization of sample preparation. Furthermore, the analysis of cell extracts had several advantages with respect to the analysis of suspensions of whole bacterial cells. Thus, spectral profiles obtained from cell extracts showed less noise and more reproducible peaks as compared to spectra obtained from intact cells [68].

MALDI-TOF can also be used for DNA determination. Recently, MALDI-TOF-MS has been applied to single nucleotide polymorphism (SNP) detection by analysis of the mass of single base extension oligonucleotides specific to the SNP of interest. Sequenom® MassARRAY® MALDI-TOF-MS were tested as a medium-throughput platform for cereal varietal identification and found that MALDI-TOF-MS could produce SNP profiles specific to barley varieties [63]. A representative mass spectrum barley variety Baudin (Multiplex C) is shown in Figure 4.

Table 2

Selected Applications of MALDI for Food Safety and Quality