Comparative proteomic analysis of the changes in mare milk associated with different lactation stages and management systems

Mare milk has traditionally been attributed a number of health promoting properties. However, knowledge on its composition and functionality remains scarce, with particularly limited studies on mare milk proteomics. This study deeply characterized mare milk proteome accounting for both caseins and proteins in the whey fraction, also addressing the impact of lactation stage and different management systems. Milk samples from Basque Mountain Horse breed mares belonging to three different farms and three lactation stages were analysed after in-gel and in-solution digestion using nLC-MS/MS. Among the 469 proteins identified, the content of alpha-1 antitrypsin was significantly higher in pasture-based compared to other systems. Moreover, lactation stage significantly affected the content of beta-lactoglobulin II, immunoglobulin-like domain-containing protein, interferon alpha-inducible protein 27, lactotransferrin, polypeptide N-acetylgalactosaminyltransferase, and transforming acidic coiled-coil containing protein 2. This study contributes to the deep characterization of mare milk proteome and provides new insights into the effect of different production factors.

Protein carbonylation sites in bovine raw milk and processed milk products

During thermal treatment of milk, proteins are oxidized, which may reduce the nutritional value of milk, abolish protein functions supporting human health, especially important for newborns, and yield potentially harmful products. The side chains of several amino acids can be oxidized to reactive carbonyls, which are often used to monitor oxidative stress in organisms. Here we mapped protein carbonylation sites in raw milk and different brands of pasteurized, ultra high temperature (UHT) treated milk, and infant formulas (IFs) after digesting the precipitated proteins with trypsin. Reactive carbonyls were derivatized with O-(biotinylcarbazoylmethyl)hydroxylamine to enrich the modified peptides by avidin-biotin affinity chromatography and analyze them by nanoRP-UPLC-ESI-MS. Overall, 53 unique carbonylated peptides (37 carbonylation sites, 15 proteins) were identified. Most carbonyls were derived from dicarbonyls (mainly glyoxal). The number of carbonylation sites increased with the harsher processing from raw milk (4) to pasteurized (16) and UHT milk (16) and to IF (24).

Influence of storage and heating on protein glycation levels of processed lactose-free and regular bovine milk products

Thermal treatment preserves the microbiological safety of milk, but also induces Maillard reactions modifying for example proteins. The purpose of this study was evaluating the influence of consumer behaviors (storage and heating) on protein glycation degrees in bovine milk products. Lactosylation and hexosylation sites were identified in ultra-high temperature (UHT), lactose-free pasteurized, and lactose-free UHT milk (ULF) and infant formula (IF) using tandem mass spectrometry (electron transfer dissociation). Overall, 303 lactosylated and 199 hexosylated peptides were identified corresponding to 170 lactosylation (31 proteins) and 117 hexosylation sites (25 proteins). In quantitative terms, storage increased lactosylation up to fourfold in UHT and IF and hexosylation up to elevenfold in ULF and threefold in IF. These levels increased additionally twofold when the stored samples were heated (40°C). In conclusion, storage and heating appear to influence protein glycation levels in milk at similar or even higher degrees than industrial processing.