Caseins, major allergens in children
Milk allergy mainly affects young infants following their initial contact with non-human proteins. It is the third most common food allergy in children, after eggs and peanuts, causing 8% of food allergies in those below the age of 15 years. Most of these children are allergic to caseins. These proteins are weakly structured, which renders them more susceptible to the action of enzymes. Therefore, they should be totally degraded during digestion and unable to induce an allergic reaction. The current upsurge in cases of milk allergy, and more specifically casein allergy, is therefore very surprising.
Blame can be placed on the intensity of thermal treatments
The hypothesis advanced by the scientists to explain the resistance of caseins to digestion incriminated the intensity of the thermal treatments applied to formula milks during their manufacture. The heating of milk can lead to the formation of protein aggregates that resist digestion more than the native proteins from which they are derived.
An in vitro model for digestion in infants to verify the hypothesis
The INRA scientists designed model, fat-free powdered milks which were subjected to thermal treatments of differing intensities. These reconstituted powders were then passed through an in vitro digestion model mimicking the physiological conditions that prevail in the digestive tract of infants (stomach and duodenum). Analysis of the digestion products of caseins clearly demonstrated an increase in the resistance of caseins to digestion with the powders subjected to the most intense thermal treatments. These results, obtained in model matrices devoid of fat, were then confirmed in more complex foods such as liquid milks.
Identification of specific domains of resistance to digestion
Overall, thermal treatments increased the resistance to digestion of all casein domains. However, according to these studies, it was particularly the hydrophobic domains – less accessible to digestive enzymes – and those carrying post-translational modifications (glycosylation, phosphorylation) that displayed the greatest resistance to the gastrointestinal tract.
Scientific leaders:
Didier Dupont
Rachel Boutrou
UMR Science et Technologie du Lait et de l’œuf,
“Science and Technology of Milk and Eggs” joint research unit
INRA – Agrocampus Ouest
65, rue de Saint-Brieuc
35 042 RENNES Cedex
For further informations:
- Dupont D., Mandalari G., Molle D., Jardin J., Rolet-Répécaud O., Duboz G., Léonil J., Mills E.N.C. and Mackie A.R. 2010. Food processing increases casein resistance to simulated infant digestion. Mol. Nutr. Food Res., 54, 1677-1689.
- Dupont D., Boutrou R., Menard O., Jardin J., Tanguy G., Schuck P., Haab B.B. and Leonil J. 2010. Heat treatment of milk during powder manufacture increases casein resistance to simulated infant digestion. Food Dig. 1, 28-39.
- R. Boutrou, E. Coirre, J. Jardin, J.Léonil. 2010. Phosphorylation and coordination link of mineral inhibit the hydrolysis of the casein (1-25) peptide by intestinal brush-border membrane enzymes. Journal of Agricultural and Food Chemistry, Vol. 58 (13): 7955-7961.
- R. Boutrou, J. Jardin, A. Blais, D. Tomé and J. Léonil. 2008. Glycosylations of k-casein-derived caseinomacropeptide reduce its accessibility to endo- but not exo- intestinal brush border membrane peptidases. Journal of Agricultural and Food Chemistry, Vol. 56: 8166-8173.
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