Invited review: Proteomics of milk and bacteria used in fermented dairy products: From qualitative to quantitative advances

Example of protein identification and quantification by isobaric tagging for relative and absolute quantitation (iTRAQ) reagents present in the aqueous phase of Swiss-type cheese. From the same profile, identification of proteins (A) as well as their quantification (B) was achieved in the same run for the 3 ripening times. The ratios d 7:d 70 or d 20:d 70 are expressed as a logarithm. The quantity of free bacterial proteins greatly increased throughout ripening, with an average factor of 6 for both bacterial species, from d 7 to 70 of ripening. However, this increase was different according to the proteins and can vary from 5- to 21-fold. Bovine proteins, which should remain constant, varied only by a factor of between 0.5 and 2. This gives an estimation of the reproducibility of the extraction and of the quantification method.