Identification of immunogenic maize proteins in a casein hydrolysate formula

Cow's milk-based formulas used for infants with cow's milk allergy are base d on hydrolyzed proteins. The formulas that are successful in preventing al lergic responses are extensively hydrolyzed. Nevertheless, reactions to suc h formulas are occasionally reported, and protein material of higher molecu lar weight than expected has been detected by binding immunoglobulin E (IgE ) from patients' sera. This paper presents the identification of high-molec ular-weight material in the extensively hydrolyzed casein formula, Nutramig en. The material was concentrated by simple centrifugation. The proteins in the pellet were separated by sodium dodecyl sulfate-polyacrylamide gel ele ctrophoresis (SDS-PAGE), and protein-containing bands were analyzed by prot ein sequencing after electroblotting. The proteins were identified as maize zeins, which are water-insoluble proteins of apparent M-r 20 000 and 23 00 0, presumably originating from the maize starch in Nutramigen. Rabbits immu nized with this formula developed antibodies against zeins but not against milk proteins. The maize zeins are probably identical to the recently repor ted components in Nutramigen (1), detected by binding of IgE from milk alle rgic patients, but not correlated to clinical allergic reactivity. The clin ical relevance of maize proteins in Nutramigen remains to be established.