Destabilization of UHT milk by protease AprX from Pseudomonas fluorescens and plasmin

Destabilization of UHT milk during its shelf life is mainly promoted by the residual proteolytic activity attributed to the psychrotrophic bacterial proteases and native milk proteases. In this study, we built skim UHT milk-based model systems to which either the major bacterial protease (AprX from Pseudomonas fluorescens), or the major native milk protease (plasmin) was added, to allow a direct comparison between the destabilization of skim UHT milk by both categories of enzymes. The physical and chemical properties were studied during 6 weeks. Our results showed AprX induced compact gels when almost all the κ-casein was hydrolyzed and the degree of hydrolysis (DH) exceeded 1.3%. Plasmin induced soft gels when around 60% of both β- and αs1-casein were hydrolyzed and the DH reached 2.1%. The knowledge gained from this study may be used for developing diagnostic tests for determining the protease responsible for UHT milk destabilisation.</p

Dataset on proteomic changes of whey protein after different heat treatment

Hereby we provide data from a shot-gun proteomics experiment, using filtered-aided sample preparation (FASP), and liquid chromatography with tandem mass spectrometry (LC-MS/MS), to relatively quantify the changes in the protein profile of whey proteins after heating milk at either 65 °C, 70 °C, 75 °C, 80 °C, or 85 °C for 30 min. The data supplied in this article supports the accompanying publication [1]. The raw mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifier “PXD016436”.</p

Effect of temperature, pH and calcium phosphate concentration on the properties of reassembled casein micelles

Reassembled casein micelles (RCMs) can be made by reassembling sodium caseinate with calcium and phosphate as well as other ions under controlled conditions into casein micelle-like structures. During the reassembly, the changes in processing parameters lead to differences in the properties of RCMs such as size, composition and structure. Understanding the effect of processing parameters on RCM properties is essential for their potential application in food products. However, the effect of process parameters has not been studied systematically. Therefore, the objective of this study was to evaluate the effect of temperature, pH and calcium phosphate concentration on the properties of reassembled casein micelles. The effect of pH on the size and structure of RCMs both during and after their formation was studied by dynamic light scattering and small-angle X-ray scattering. We found that pH affects both the size and internal structure of RCMs. We could also modulate the size and composition of RCMs by changing the temperature and calcium phosphate concentration. The insights of this study not only can be used to modulate the composition and structure of RCMs, but also help us to understand how processing parameters will influence the assembly of RCMs from novel sources, such as recombinant caseins

Effect of temperature, pH and calcium phosphate concentration on the properties of reassembled casein micelles

Reassembled casein micelles (RCMs) can be made by reassembling sodium caseinate with calcium and phosphate as well as other ions under controlled conditions into casein micelle-like structures. During the reassembly, the changes in processing parameters lead to differences in the properties of RCMs such as size, composition and structure. Understanding the effect of processing parameters on RCM properties is essential for their potential application in food products. However, the effect of process parameters has not been studied systematically. Therefore, the objective of this study was to evaluate the effect of temperature, pH and calcium phosphate concentration on the properties of reassembled casein micelles. The effect of pH on the size and structure of RCMs both during and after their formation was studied by dynamic light scattering and small-angle X-ray scattering. We found that pH affects both the size and internal structure of RCMs. We could also modulate the size and composition of RCMs by changing the temperature and calcium phosphate concentration. The insights of this study not only can be used to modulate the composition and structure of RCMs, but also help us to understand how processing parameters will influence the assembly of RCMs from novel sources, such as recombinant caseins

Use of UV Treated Milk Powder to Increase Vaccine Efficacy in the Elderly

Aging populations experience a decline in adaptive immune system function also known as immunosenesence. Protein nutrition has been shown to stimulate and strengthen the immune system, and such approaches are needed for this growing segment of the population. A controlled, randomized, double blind pilot study was conducted to compare two different protein sources (soy and dairy) as nutritional supplementation to enhance vaccine response. Our objective was to examine the immune stimulating effects of dairy protein subjected to ultraviolet radiation (UV-C) radiation treatment process instead of pasteurization. Participants were 21 healthy individuals over 60 years of age who consumed 6 g of the dairy protein or a comparison, soy isoflavone protein, twice a day for 8 weeks. DTaP vaccine administered at week 4. Non-parametric t-tests revealed a significant increase in Tetanus antibodies in the dairy group compared to the soy group at week 8. These findings suggest additional benefits of UV-C treated unheated dairy protein as a solution to counteract immunosenescence, but warrant further study in elderly and other populations that might benefit from immune system stimulation

The Host Defense Proteome of Human and Bovine Milk

Milk is the single source of nutrients for the newborn mammal. The composition of milk of different mammals has been adapted during evolution of the species to fulfill the needs of the offspring. Milk not only provides nutrients, but it also serves as a medium for transfer of host defense components to the offspring. The host defense proteins in the milk of different mammalian species are expected to reveal signatures of evolution. The aim of this study is therefore to study the difference in the host defense proteome of human and bovine milk. We analyzed human and bovine milk using a shot-gun proteomics approach focusing on host defense-related proteins. In total, 268 proteins in human milk and 269 proteins in bovine milk were identified. Of these, 44 from human milk and 51 from bovine milk are related to the host defense system. Of these proteins, 33 were found in both species but with significantly different quantities. High concentrations of proteins involved in the mucosal immune system, immunoglobulin A, CD14, lactoferrin, and lysozyme, were present in human milk. The human newborn is known to be deficient for at least two of these proteins (immunoglobulin A and CD14). On the other hand, antimicrobial proteins (5 cathelicidins and lactoperoxidase) were abundant in bovine milk. The high concentration of lactoperoxidase is probably linked to the high amount of thiocyanate in the plant-based diet of cows. This first detailed analysis of host defense proteins in human and bovine milk is an important step in understanding the function of milk in the development of the immune system of these two mammals

Lysine blockage of milk proteins in infant formula impairs overall protein digestibility and peptide release

During heat processing of milk and dairy products, for example infant formula, the Maillard reaction occurs. In vitro and animal studies suggest that Maillard reaction induced lysine blockage impairs protein digestibility. Most studies that investigate the effect of glycation on protein digestion use a mixture of isolated milk protein with reducing sugars. In this study, infant formulas with 6.5%, 8.4%, 11.2%, 14.8%, 20.8%, and 44.5% of blocked lysine (BL) were digested in an in vitro infant digestion model and tested for protein hydrolysis and peptide release. OPA (o-phthalaldehyde) assay was used to assess the degree of protein hydrolysis. SDS-PAGE was conducted to monitor the hydrolysis of specific proteins. Peptides formed after gastric and intestinal digestion were identified by LC/MS. Protein hydrolysis of the 6.5% BL sample was significantly higher after 10 minutes of intestinal digestion compared to all other samples. Most differences were observed after intestinal digestion. A significant change in peptide patterns was observed for the 45% BL sample resulting in a relatively higher number of peptides with more than 14 amino acids. Mainly casein-derived peptides were affected. Overall, the average peptide length was significantly increased for the 44.5% BL glycated product (on average 10.2 amino acids for 6-21% BL vs. 11.4 amino acids for 45% BL; p < 0.001). In conclusion, glycation of milk proteins in an infant formula product can impair overall protein digestibility. These findings emphasize the importance of mild processing and having low BL levels in infant formula to ensure optimal digestion of proteins.</p

Effect of Processing Intensity on Immunologically Active Bovine Milk Serum Proteins

Consumption of raw cow's milk instead of industrially processed milk has been reported to protect children from developing asthma, allergies, and respiratory infections. Several heat-sensitive milk serum proteins have been implied in this effect though unbiased assessment of milk proteins in general is missing. The aim of this study was to compare the native milk serum proteome between raw cow's milk and various industrially applied processing methods, i.e., homogenization, fat separation, pasteurization, ultra-heat treatment (UHT), treatment for extended shelf-life (ESL), and conventional boiling. Each processing method was applied to the same three pools of raw milk. Levels of detectable proteins were quantified by liquid chromatography/tandem mass spectrometry following filter aided sample preparation. In total, 364 milk serum proteins were identified. The 140 proteins detectable in 66% of all samples were entered in a hierarchical cluster analysis. The resulting proteomics pattern separated mainly as high (boiling, UHT, ESL) versus no/low heat treatment (raw, skimmed, pasteurized). Comparing these two groups revealed 23 individual proteins significantly reduced by heating, e.g., lactoferrin (log2-fold change = -0.37, p = 0.004), lactoperoxidase (log2-fold change = -0.33, p = 0.001), and lactadherin (log2-fold change = -0.22, p = 0.020). The abundance of these heat sensitive proteins found in higher quantity in native cow's milk compared to heat treated milk, renders them potential candidates for protection from asthma, allergies, and respiratory infections