To assess changes in the antigenicity of gliadin during proteolysis, two model systems of hydrolysis using pepsin or trypsin in the presence of urea or dioxan were tested. Rabbit polyclonal antibodies against whole gliadin were used in two ELISA procedures. The first one involved direct analysis of antigliadin antibody binding. The second one used anti-immunoglobulin Ci antibodies to indirectly test the antigliadin antibodies reacting with hydrolysis products. The antigenicity of pepsin-hydrolysed gliadin decreased only slowly during hydrolysis and was maintained at about 45% of the initial value for up to 24 h. Qualitatively, after 3 h of hydrolysis, antigenic reactivity pattern seemed to reveal some marked conformational changes. Tryptic hydrolysis failed to modify significantly the antigenicity in either denaturing agent (urea or dioxan).

When alkali-treated casein (NaOH, 0·2n, 80°C, 1h) was given as sole protein source at a suboptimal level (10% dry matter) to rats, reduced food intake (46%) and an arrest of growth were observed. Both these parameters were increased, to a level similar to control rats receiving the 10% protein diet, by either increase of protein level from 10% to 20% or by supplementation with CYS, MET, VAL, THR, TYR. In adult rats, food intake was not impaired but growth rate was greatly reduced.

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.

Alkali treatment of casein, in the presence of 0·1n or 0·2n sodium hydroxide, at 80°C for 1h, leads to a loss of amino acids and to the formation of lysinoalanine; in the rat, growth, protein efficiency ratio and nitrogen digestibility are decreased. The addition of cysteine (6·1 g/100 g casein) as a reducing agent during the alkali treatment of casein avoids the formation of lysinoalanine and the harmful biological effects of alkali treatment. Sulphur amino acid (l-cysteine or dl-methionine) supplementation of treated casein, added after the alkali treatment, is without beneficial effect.

Casein is submitted to a severe alkaline treatment (NaOH 0,2 or 0,5 N, 1 hr., 80 degrees C). The hydrolysis by pancreatic enzymes (trypsin or chymotrypsin) is reduced in vitro and, in the case of the more severe treatment, stopped. After an extended (24 hrs.) trypsin and pronase hydrolysis, it is shown, by affinity chromatography, that peptides, which are not hydrolysable, can bind to trypsin and inactivate this enzyme in vitro.

Digestive transit in rats receiving an alkali-treated casein.Rats ingesting alkali-treated casein (NaOH, 0.2 N, 80 °C, 1 hr) showed diarrhea, a reduction of digestibility and pancreatic hypertrophy.However, neither dry matter ingestion rhythms nor overall gastrointestinal transit time were modified.The diarrhea might account for poor digestive utilization of the protein.Introduction.