In vitro digestion of cow's milk proteins by duodenal juice from infants with various gastrointestinal disorders.

The hydrolysis of bovine alpha-lactalbumin, beta-lactoglobulin, and casein by duodenal juice from 20 infants (18 with normal exocrine pancreatic function, 2 with pancreatic insufficiency), aged 3-19 months was studied in vitro with the aid of electroimmunoassay and sodium dodecyl sulfate-poly-acrylamide gel electrophoresis. The results from the two methods were almost identical. Duodenal juice from infants with cow's milk protein intolerance (7), celiac disease (5), and unclassified gastrointestinal disorder (6) had the same capacity to hydrolyze the milk proteins. No hydrolysis occurred in the two patients with pancreatic insufficiency. The hydrolyzing capacity was not correlated with age in the actual age group. The hydrolysis of the milk proteins occurred at a considerably slower rate when the proteins were crude, as in cow's milk, adapted, or unadapted formula, than when they were in a purified form. About 1 mg of purified alpha-lactalbumin or beta-lactoglobulin, and about 30 mg of purified casein could be hydrolyzed per milliliter duodenal juice per minute. Corresponding figures for the hydrolysis of the various proteins in cow's milk were 0.03, 0.12, and 16.1 mg/ml duodenal juice/min. Preincubation (60 min) with gastric aspirate after adjusting pH to 4-5 did not change the results. In conclusion, the duodenal juice from infants with normal exocrine pancreatic function has a great ability to hydrolyze casein. Corresponding hydrolytic capacity for alpha-lactalbumin or beta-lactoglobulin is considerably lower.