Peptidomic approach, based on liquid chromatography/electrospray ionization tandem mass spectrometry, for detecting sheep's milk in goat's and cow's cheeses

Abstract

A common fraud in the dairy field is the addition of sheep's milk to goat's cheeses, because it has a very similar taste to goat's milk, but is more available, and is commonly considered to have a better capacity to curdle. For similar reasons, and due to economic convenience, sheep's cheeses may also contain fraudulent cow's milk. In order to detect this fraud, an EU official method may be used, but it is only a qualitative method (presence/absence of cow's milk). A method able to quantify the presence of sheep's milk during cheese production in goat's and cow's cheeses was developed. The method is based on liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) analysis of peptides of a casein extract from the cheese. By a simple procedure, caseins are extracted from cheeses, solubilized, digested with plasmin, and subsequently analyzed by LC/ESI-MS/MS. A typical sheep's peptide produced by plasmin hydrolysis (m/z = 860) was accurately selected and analyzed to understand if, and by how much, a declared pure goat's cheese contains sheep's milk. By analyzing the same peptide it is also possible to detect if, and by how much, a declared pure sheep's milk contains, or not, cow's milk. The method was applied to several goat's and cow's cheese samples. Quantitation was performed with a calibration curve obtained by analyzing curd cheeses containing different percentages of sheep's milk. The method detection limit and method quantitation limit were evaluated. This method appears accurate and suitable for detecting up to 2% of sheep's milk in cheeses.

Characterization of sheep milk fat globule proteins by two-dimensional polyacrylamide gel electrophoresis/mass spectrometry and generation of a reference map

“…Knowledge of protein chemistry has been used by the dairy industry in different ways: among many others, for a better understanding of the cheesemaking potential of milks containing different genetic variants of caseins (Pirisi et al, 1999), for investigating protein stability (O'Donnell et al, 2004) and for quality control (Guarino et al, 2010). However, while the major protein components of milk have been the subject of intense research and characterization, less abundant milk proteins and peptides have lagged behind, and studies have been mostly performed in humans and bovines.…”

Farm animal milk proteomics

“…Thus it is important to characterize proteins secreted by bacterial starters in cheese as a marker of the ripening or fermentation process [165,166]. Moreover, the mandatory evaluation of the safety and traceability [167,168] of these important dairy products can be achieved monitoring specific protein or peptide products [169].…”

Proteomics in Food Science

“…␤-lactoglobulin whey protein has also been used for the detection and quantification of cow milk adulteration in goat milk or in either goat or sheep milk (Müller et al, 2008) by means of an HPLC-ESI-MS or a capillary electrophoresis-MS method, respectively, using retention times and accurate molecular masses to detect the presence of cow milk at levels as low as 5%. Guarino et al (2010) developed an LC-ESI-MS/MS method based on the detection of a sheep-specific peptide from the digestion of casein, a method that is able to detect up to 2% of sheep milk in goat and cow cheeses. Species-specific casein peptides have also been used for the detection and quantification of bovine, ovine, buffalo, and caprine milks in milk mixtures, using MALDI-MS or LC-ESI MS methods that are able to detect extraneous milk concentrations as low as 0.5% (Cuollo et al, 2010).…”