## 2 An Outline of Proteomics
### Proteomic Analyses in Meat Safety and Authenticity  
Proteomic analyses have been widely used in the identification of new markers that are suitable to distinguish accidental contamination from intentional adulteration using LC-MS/MS methods, based on a detection limit of less than 1% (\(w/w\)). Generally, they identify species-specific markers which are also stable during food processing [20]. Moreover, proteomic analyses have been used in order to detect fraud and adulteration of different animal species and issues in production systems, postmortem processing and storage [31]. Intentional modifications of product composition can be associated with food proteins. Proteomics are able to provide quick information regarding the food proteins in this regard. As a result, the relevant information can be effectively used for its correlation with food allergies in consumers because of undeclared compounds. Safety and authenticity issues are successfully addressed [5]. According to [PERSON] et al. [32], marker peptides were detected in a complex food matrix such as Bolognese sauce samples. Undoubtedly, these processed meat products are highly associated with adulteration. [PERSON] et al. 's validated method demonstrated a good specificity (the limit of detection (LOD): 0.2-0.8% in the finished product) and sensitivity in authentication of eight meat species (duck, rabbit, chicken, turkey, buffalo, equine, deer and sheep). The rapid parallel reaction monitoring (PRM) method was developed using high-resolution Orbitrap MS in order to detect pork meat. When the most sensitive peptide was selected, the LOD in mixed meat can reach 0.5%. The relative standard deviation (RSD) values between detected and designated pork levels (1%, 5% and 50%) were 4-15%. A total of 125 peptides were identified; however, only 5 peptide markers were selected, derived from myosin-1 and myosin-4, which could be used for authenticating pork meat in mixtures of sheep, beef and chicken. Nevertheless, the respective peptide markers were heat-sensitive and, as a result, this method can only be applied for authentication of raw meat samples rather than cooked [33]. Notwithstanding the above method, [PERSON] et al. [34] developed another accurate OFFGEL electrophoresis method together with a label-free mass spectrometric-based proteomics approach, which could be used in both raw and cooked meat mixes containing cattle, water buffalo, sheep and goat meat. In this investigation, species-specific peptides derived from myosin light chain-1 and -2 were recognized for authenticating buffalo meat spiked at a minimum 0.5% level in sheep meat with high confidence. Relative quantification of buffalo meat mixed with sheep meat was carried out by ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) and the PLGS search engine to substantiate the confidence level of the data. In the DNA-based method, PCR amplification of the mitochondrial D loop gene using species-specific primers found 226 bp and 126 bp product amplicons for buffalo and cattle meat, respectively. These authors reported that this method was effective in detecting a minimum of 0.5-1.0% when buffalo meat was spiked with cattle meat in raw and cooked meat combinations. The same trends were reported by [PERSON] et al. (2018) who developed a 2 DE and OFFGEL-based proteomic approach for authenticating raw and cooked water buffalo, sheep and goat meat and their blends. In-gel and OFFGEL-based proteomic approaches are effectual in validating meat mixes spiked at minimum 1.0% and 0.1% levels, respectively, in triple meat mixes for both raw and cooked samples. Electrophoretic approaches for meat authentication display certain limitations, for example, in the investigation of hydrophobic and poorly solvable proteins, the limited dynamic series of the obtainable detection methods, great complexity and the dynamic range of the proteins in the sample.