# Proteomics Analysis in Dairy Products: Cheese, a Review
## 7 Starters and Proteomics
### Lactobacillus
A decrease was found in the amount of proteins responsible for sugar transport, glycogen biosynthesis, pentose phosphate pathway, exopolysaccharide (EPS) biosynthesis and cell wall biosynthesis [53]. The bacterial exoproteome of _Lactobacillus_ is responsible for the hydrolysis of macromolecules, such as polysaccharides, proteins and anti-nutritional compounds; the uptake of nutrients, the communication with other prokaryotic and eukaryotic cells and the colonization of organic and inorganic surfaces [57; 67]. For the detection of exoproteome gel-based and, especially, gel-free proteomics are mainly used [57; 68]. The S-layer proteins (SlpA, SlpB, and SlpX) of _L. acidophilus_ strains have adhesive properties and they are involved in the adhesion to intestinal epithelial Caco-2 cells and induction of inflammatory cytokine IL-12 [57; 69; 70]. S-layer proteins of _L. acidophilus_ and _L. helicticus_ strains are also involved in TH-29 cells survival in simulated gastric and intestinal juices and in adhesion capacity of those [57; 71]. Recently, LC-MS/MS analyses of the surface-associate proteome (surfaceome), released by trypsin shaving of _L. rhamn_ strains, identified 102 and 198 proteins from GG and Lc705 strains, respectively [57; 72]. Comparative surface-associate proteome (surfaceome) analysis pointed out differences between bacteria strains associated with adaptation to specific niches (response to bile, hydrolysis of casein, host response with immune functions). Most of the identified proteins were moonlighting proteins (e.g., DnaK, GroEL, EFTtu, LDH, GAPDH, Eno, PGK). Specific moonlighting antigens were detected in _L. rhamn_ strains [72]. Many moonlight proteins (e.g., GAPDH, Eno and EF-Tu) were also identified in the secretome of other _Lactobacillus_ strains [73; 74; 75; 76; 77; 78; 79]. The mechanisms by which cytosolic proteins change location, regarding moonlighting function, are not completely understood [80]. The adhesion capacity of _Lactobacillus_ was affected during growth and changes in the environmental conditions, as the composition of secretome altered [72; 73; 81]. Labeling of bacterial surface proteins and DIGE separation, followed by MS analysis of _L. rhamn_, highlighted that bile stress affected the abundance of surfaceome proteins (including DnaK, LDH, GAPDH, Eno, PG) [82] whereas proteins N-acetyl-glucosamine (GlcNAcNAc) acetylase (NagA) and GlcNac deaminase/isomerate (NagB) involved in the catabolism of GlcNAc were oversentihetized by _L. rhamn_ GG and _L. casei_[82; 83; 84]. NagA and NagB were also oversentihetized by acid stressed _L. casei_ cells [57]. Compared to optimal conditions of growth, surface antigen (LGG_02016) and predicted cell wall hydrolase (NLP/P60 domain) of _L. rhamn_ cells were ratcheted up under acidic conditions [85]. _Lactobacillus_ cells (e.g., _L. plantarum_ DB200) increased the levels of surface proteins like bacteriocins, molecular chaperones, enzymes, lipoproteins, and surface layer under biofilm conditions [74; 75; 86]. In general, proteins, which are associated with carbohydrate binding and metabolism, protein synthesis, lipid degradation, amino acid binding, and stress tolerance, are found in _Lactobacillus_ spp. [57].