Pasteurization of cow’s milk can cause proteins and other molecules to trigger allergic reactions, especially in newborns who have undeveloped or insufficient microorganisms in their gastrointestinal tracts to aid in digestion. This heating process can cause milk proteins to change shape, which inhibits their absorption through the small intestine and causes them to be absorbed instead by Peyer’s patches in the gastrointestinal tract, thereby inducing allergies through a cascade of molecular events.
Peyer’s Patches and Allergies
Clinically important food allergens tend to form aggregates, collections of proteins forming clusters, that cannot pass through the epithelial cell layer of the intestine. Instead, these allergens are absorbed by lymphoid nodules called Peyer’s patches, located in the ileum of the small intestine. Researchers from Mount Sinai School of Medicine in New York City found that pasteurization alters the structure of the milk proteins alpha-lactalbumin, beta-lactoglobulin and casein that can promote allergic reactions to milk. Their results, published in the July 2008 issue of “Allergy,” found that pasteurization of milk leads to the aggregation of these proteins and uptake by Peyer’s patches, which promotes production of inflammatory molecules that can elicit anaphylaxis, an immediate and aggressive allergic reaction that can impede breathing. The study concluded that milk proteins can promote anaphylaxis when orally administered to sensitive individuals.
Homogenization and Pasteurization
Homogenization is the mixing of milk derived from different herds of cows and/or dairies to produce uniform raw milk prior to pasteurization. Some individuals can tolerate unpasteurized cow’s milk, but suffer from hypersensitivity reactions from homogenized and pasteurized milk. A study in the May 2003 issue of “The Journal of Dairy Research” compared the tolerance of homogenized and unhomogenized milk cow’s in 44 lactose-tolerant volunteers over five days. The study found no differences in allergic symptoms between the two types of milk processing, leading the authors to conclude that homogenization does not play a role in milk allergies, leaving pasteurization as the probable cause of hypersensitivity reactions caused by milk consumption.
Allergies to Milk in Infants
Breast milk contains important immune factors that compensate for the lack of defense mechanisms in the gut of newborns. Because of their immature immune systems, feeding newborns cow’s milk before four to six months of age can induce allergic reactions to cow’s milk, according to an article in the January 2000 issue of “Advances in Experimental Medicine and Biology.” Researchers studied the effects of cow’s milk consumption on allergies in over 6,000 newborns in a Finnish maternity hospital. Of these, 2.4 percent of exclusively breast-fed infants showed symptoms of allergy to pasteurized cow’s milk. The study found that infrequent exposure to small amounts of cow’s milk during the first eight weeks of life can induce the development of allergy.
TGF-Beta-1
Cytokines, which are immune system signaling molecules, have been identified as potential inhibitors of allergens present in pasteurized cow’s milk. A study in the February 2009 issue of “Pediatric Allergy and Immunology” investigated the effects of pasteurization and filtration on allergies to cow’s milk formulas. Researchers from the Pediatric Department of the University of Verona in Italy identified a cytokine called TGF-beta-1 in raw unpasteurized cow’s milk that they suspected of contributing to the prevention of cow’s milk allergies in infants. The study found that minute concentrations of TGF-beta-1 may contribute to the development of the immature gastrointestinal tracts of infants to thwart allergic disorders caused by consumption of pasteurized milk.
References
- “Allergy”; Pasteurization of Milk Proteins Promotes Allergic Sensitization by Enhancing Uptake Through Peyer's Patches; F. Roth-Walter, et al.; July 2008
- “The Journal of Dairy Research”; No Difference in Symptoms During Challenges With Homogenized and Unhomogenized Cow's Milk in Subjects with Subjective Hypersensitivity to Homogenized Milk; L. Paajanen, et al.; May 2003
- “Advances in Experimental Medicine and Biology”; Breast-Feeding and the Development of Cows' Milk Protein Allergy; K. Saarinen, et al; January 2000
- “Pediatric Allergy and Immunology”; Transforming Growth Factor-Beta is Elevated in Unpasteurized Cow's Milk; Diego D. Peroni, et al.; February 2009
