Protein-bound and free glycation compounds in human milk: A comparative study with minimally processed infant formula and pasteurized bovine milk.

The role of the Maillard reaction and the accumulation of non-enzymatic glycation compounds in human milk have been scarcely considered. In this study, we investigated the proteins most susceptible to glycation, the identity of the corresponding modified residues and the quantitative relationship between protein-bound and free glycation compounds in raw human milk and, for comparison, in minimally processed infant formula and pasteurized bovine milk. In human milk, total protein-bound lysine modifications were up to 10% of the counterparts in infant formula, while Nε-carboxymethyllysine reached up to 27% of the concentration in the other two products. We demonstrated that the concentration of free pyrraline and methylglyoxal-hydroimidazolone were of the same order of magnitude in the three milk types. Our results delineate how the occurrence of some glycation compounds in human milk can be an unavoidable part of the breastfeeding and not an exclusive attribute of infant formulas and pasteurized bovine milk.

Albumen and Yolk Plasma Peptidomics for the Identification and Quantitation of Bioactive Molecules and the Quality Control of Hen Egg Products.

Hen eggs and the corresponding food products are essential components of human diet. In addition to supplying basic nutrients, they contain functional peptides that are released in vivo within the intact raw material following physiological proteolytic events affecting specific proteins or derive from technological processing of albumen and yolk fractions as a result of the dedicated use of proteases from plant and microbial sources. Besides their potential importance for functional applications, peptides released under physiological conditions in intact egg can be used as markers of product storage and deterioration. Therefore, characterization and quantitation of peptides in egg and egg-derived products can be used to implement evaluation of potential bioactivities as well as to assess food product qualitative characteristics. Here, we provide dedicated information on extraction, identification, and quantitative analysis of peptides from albumen and yolk plasma; nano-liquid chromatography-mass spectrometry combined with bioinformatic analysis of resulting raw data by different software tools allowed to assign molecules based on database searching and to evaluate their relative quantity in different samples.

Proteomic Characterization of Native and Rearranged Disulfide Bonds in Proteins from Thermally Treated and Commercial Milk Samples.

To investigate thiol-disulfide interchange reactions in heated milk yielding non-native intramolecular rearranged and intermolecular cross-linked proteins, a proteomic study based on nanoLC-ESI-Q-Orbitrap-MS/MS and dedicated bioinformatics was accomplished. Raw milk samples heated for different times and various commercial dairy products were analyzed. Qualitative experiments on tryptic digests of resolved protein mixtures assigned the corresponding disulfide-linked peptides. Results confirmed the limited data available on few milk proteins, generated the widest inventory of components (63 in number) involved in thiol-disulfide exchange processes, and provided novel structural information on S-S-bridged molecules. Quantitative experiments on unresolved protein mixtures from both sample typologies estimated the population of molecules associated with thiol-disulfide reshuffling processes. Disulfide-linked peptides associated with native intramolecular S-S bonds generally showed a progressive reduction depending on heating time/harshness, whereas those related to specific non-native intramolecular/intermolecular ones showed an opposite quantitative trend. This was associated with a temperature-dependent augmented reactivity of definite native protein thiols and S-S bridges, which determined the formation of non-native rearranged monomers and cross-linked oligomers. Results provided novel information for possibly linking the nature and extent of thiol-disulfide exchange reactions in heated milk proteins to the corresponding functional and technological characteristics, with possible implications on food digestibility, allergenicity, and bioactivity.

An odorant-binding protein in the elephant's trunk is finely tuned to sex pheromone (Z)-7-dodecenyl acetate.

Chemical communication in elephants has been well studied at the chemical and behavioural levels. Pheromones have been identified in the Asian elephant (Elephas maximus), including (Z)-7-dodecenyl acetate and frontalin, and their specific effects on the sexual behaviour of elephants have been accurately documented. In contrast, our knowledge on the proteins mediating detection of pheromones in elephants remains poor and superficial, with only three annotated and reliable entries in sequence databases, two of them being odorant-binding proteins (OBPs), and the third a member of von Ebner's gland (VEG) proteins. Proteomic analysis of trunk wash extract from African elephant (Loxodonta africana) identified one of the OBPs (LafrOBP1) as the main component. We therefore expressed LafrOBP1 and its Asian elephant orthologue in yeast Pichia pastoris and found that both recombinant proteins, as well as the natural LafrOBP1 are tuned to (Z)-7-dodecenyl acetate, but have no affinity for frontalin. Both the natural and recombinant LafrOBP1 carry post-translational modifications such as O-glycosylation, phosphorylation and acetylation, but as these modifications affect only a very small amount of the protein, we cannot establish their potential effects on the ligand-binding properties of OBP1.