Changes in Milk Protein Interactions and Associated Molecular Modification Resulting from Thermal Treatments and Storage

Abstract

We investigated protein modifications that occur during short‐ and long‐term storage of raw, pasteurized, and ultra‐high‐temperature processed (UHT) milks using RE‐HPLC and redox proteomics. The RE‐HPLC results show that casein dissociation and whey protein/κ‐casein association occurred in both pasteurized and UHT milk. The extent of protein interactions was more pronounced in UHT milk after storage. The redox proteomics analyses show that primary structural level protein modifications were not correlated to processing type on the of day processing but did occur and increase during storage. Methionine oxidation was the most significant type of oxidative modification in all samples, particularly in the caseins. Methionine oxidation increased in the UHT‐treated milk samples with longer storage times, especially in the micelle‐phase proteins, likely due to the increasing exposure of these proteins as they migrated to the serum phase. Glycated and lactosylated early‐stage Maillard reaction products were also found after heat treatment, particularly in UHT‐treated milk, with the levels of these products maintained and generally increased with increasing storage time. Practical Application Understanding changes in protein modification during heat processing and storage of liquid milk products may help develop a model to predict the quality and shelf‐life stability of heat treated milk products.

Influence of Pasteurization and Storage on Dynamic In Vitro Gastric Digestion of Milk Proteins: Quantitative Insights Based on Peptidomics

“…Low numbers of peptides from β-Lg were detected in raw milk during gastric digestion (0, 1, 2, and 5 peptides at 10, 30, 60, and 120 min of digestion, Supplementary Materials Figure S5C), which was consistent with native β-Lg's resistance to pepsin hydrolysis [35]. The peptides from the regions 28-44, 58-70, and 112-120 were detected in PM0d at 10 min, indicating that pasteurization induced conformational changes in β-Lg and thus increased the susceptibility to pepsin action [14]. No new peptides were found in PM0d at 30 min, indicating that the hydrolysis of β-Lg in heated milk mainly occurred during the initial period of gastric digestion.…”

“…Therefore, it needs to be stored at 4-6 • C and has a shelf-life of approximately 7 days from a microbiological safety point of view [13]. Some association and dissociation of milk proteins occur in pasteurized milk during storage, despite the short shelf-life and low storage temperature [14,15]. Modification of the surface hydrophobicity of proteins and a marked increase of the casein micelle size were observed in pasteurized milk upon cold storage [15].…”

Conjugation of milk proteins and reducing sugars and its potential application in the improvement of the heat stability of (recombined) evaporated milk

“…On the other hand, the pre-heating treatment had limited impact on the glycation behavior of β-casein. Lactosylated early-stage Maillard reaction products were found in milk after heat treatment, particularly in UHT-treated milk (at 141 • C for 2 s), with the levels of these products increasing with increasing storage time (Liu et al, 2019). Balde and Aider (2019) found that vacuum evaporation favored the loss of free amino groups in skim milk as compared to cryo-concentration and reverse osmosis concentration.…”

Review of antimicrobial peptides as promoters of food safety: Limitations and possibilities within the food industry

“…Their presence in the amino acid sequence increases the membrane binding ability of peptides; hydrogen bonds assist in the interaction with negatively charged surfaces (Jindal, Le, Mohd Yusof, & Sekaran, 2014). Modification of AMPs' net charge has been used to enhance their activity, as evidenced in a study by Liu et al (2019). Their results showed that the positive charge was increased via substitution of alanine for lysine in a peptide analogous to phylloseptin‐PHa (PSPHa1).…”