Peptide Release after Simulated Infant In Vitro Digestion of Dry Heated Cow’s Milk Protein and Transport of Potentially Immunoreactive Peptides across the Caco-2 Cell Monolayer

Abstract

Dry heating of cow’s milk protein, as applied in the production of “baked milk”, facilitates the resolution of cow’s milk allergy symptoms upon digestion. The heating and glycation-induced changes of the protein structure can affect both digestibility and immunoreactivity. The immunological consequences may be due to changes in the peptide profile of the digested dry heated milk protein. Therefore, cow’s milk protein powder was heated at low temperature (60 °C) and high temperature (130 °C) and applied to simulated infant in vitro digestion. Digestion-derived peptides after 10 min and 60 min in the intestinal phase were measured using LC-MS/MS. Moreover, digests after 10 min intestinal digestion were applied to a Caco-2 cell monolayer. T-cell epitopes were analysed using prediction software, while specific immunoglobin E (sIgE) binding epitopes were identified based on the existing literature. The largest number of sIgE binding epitopes was found in unheated samples, while T-cell epitopes were equally represented in all samples. Transport of glycated peptide indicated a preference for glucosyl lysine and lactosyl-lysine-modified peptides, while transport of peptides containing epitope structures was limited. This showed that the release of immunoreactive peptides can be affected by the applied heating conditions; however, availability of peptides containing epitopes might be limited.

Effect of Phosphorylation on the Structure and Emulsification Properties of Different Fish Scale Gelatins

“…In the emulsion system, by introducing negatively charged phosphate groups, the droplets gain a strong electrostatic repulsive force, which improves the surface charge intensity of the droplets. This leads to better spatial stability and prevents aggregation and coalescence between the droplets [23,27,28]. For samples with reduced zeta potential, this may be attributed to the formation of aggregates, because the decrease in surface charge may be related to the exposure of hydrophobic non-polar residues through the expansion of the tertiary structure.…”

“…With the increasing negative charges introduced by phosphate groups along the protein molecular surface, the hydration of protein will be enhanced and lead to the improvement in water solubility [8,24]. The phosphorylation of the lysine site in gelatin hinders the hydrolysis of lysine residues in gelatin and reduces the content of lysine, so the content of amino acids is reduced [28]. The three kinds of fish scale gelatins had different reduction rules of amino acids, which was due to different degrees of phosphorylation reaction.…”

In vitro simulated semi-dynamic gastrointestinal digestion: evaluation of the effects of processing on whey proteins digestibility and allergenicity

“…For example, it has been shown that lysine blockage induced a significant change in the peptide pattern after simulated infant gastrointestinal digestion. 6 Heat treatment reduced significantly available lysine of skim milk powder measured in growing rats. [7][8][9] However, the effect of thermal processing on protein digestibility is still controversial since protein denaturation may enhance digestibility by the exposure new cleavage sites to the action of the digestive enzymes, but protein aggregation and glycation impairs protein digestibility.…”

Transport of a Peptide from Bovine αs1-Casein across Models of the Intestinal and Blood–Brain Barriers

“…In particular, differentiated Caco-2 monolayers display cell polarization, microvillus structure, carrier-mediated transport systems and tight junctions, and are therefore considered well suited for studies of intestinal uptake [6,7]. In vitro studies have shown that bioactive milk peptides can cross Caco-2 monolayers, e.g., ACE-inhibitory peptides from β-lactoglobulin and whey hydrolysates [8,9], IgE immunoreactive peptides from simulated infant digestion [10], the opioid peptides β-casomorphin-5 and β-casomorphin-7 [11], two anxiolytic peptides from αs 1 -casein [12] and a 17 residue immunomodulatory peptide from β-casein [13]. In vivo, the caseinomacropeptide (residues 106-169 of κ-casein) has been detected in plasma from newborns after breastfeeding and formula feeding, as well as in adult plasma after milk or yogurt ingestion [14,15].…”