Effect of severely alkali-treated casein on gastrointestinal transit and selected intestinal enzyme activities

Alkaline treatment of proteins leads to chemical changes which alter the proteins' digestibility. Severely alkali-treated casein (0.2N NaOH, 80 degrees C, 1 hour) in the diet reduces food intake and growth of young but not of adult Sprague Dawley rats. Gastrointestinal transit time is not reduced significantly in either young or adult rats. Food intake and growth rate are improved by amino acid supplementation. In this case, protein content and total leucine aminopeptidase activity are increased in the distal part of the small intestine whereas gamma-glutamyl-transpeptidase and maltase activities are increased in both the proximal and distal parts. Alkaline phosphatase activity remains unchanged. These intestinal adaptations differ from those observed in rats receiving a diet containing untreated casein and graded levels of a synthetic trypsin inhibitor. In the latter, protein digestibility remains high, gamma-glutamyltranspeptidase and also maltase activities are increased in the proximal and medial parts of the small intestine only. Intestinal adaptation in rats receiving alkali-treated casein does not result from a deficiency of pancreatic proteases activity. Ileal accumulation of undigested peptides from insufficient hydrolysis of alkali-treated casein may account for these mucosal adaptations.