[In vitro proteolysis of casein and gluten by pancreatic enzymes].

The time-course of proteolysis of casein and gluten by pancreatic enzymes (trypsin, chymotrypsin, pancreatic juice) was studied in vitro with various concentrations of enzyme or substrate. The effect of a previous peptic proteolysis, with or without sodium phytate, on proteolysis by pancreatic juice was also studied. Proteolysis was evaluated by measuring the nitrogen in products solubilized in trichloroacetic acid (peptides + amino acids) and in phosphotungstic acid (amino acids). Without a previous peptic proteolysis, at a low enzyme/substrate ratio, the release of peptides and amino acids was greater for casein than for gluten. At a high enzyme/substrate ratio, peptide release by pancreatic juice and chymotrypsin was quite similar for casein and gluten but amino acid release was a little less for gluten. After a previous high peptic proteolysis without sodium phytate, pancreatic juice proteolysis, at a low enzyme/substrate ratio, was increased. Peptide release was similar for casein and gluten but amino acid release was a little less for the gluten. With sodium phytate, the release of peptides was quite similar for casein but was less for gluten. The release of amino acids was diminished in both cases. Thus, gluten was more resistant than casein to the action of pancreatic enzymes. Nevertheless, this was not necessarily observed when those enzymes were used for proteolysis at a high enzyme/substrate ratio or following a high peptic proteolysis. The differences between casein and gluten proteolyses have been discussed according to the specific action of the pancreatic enzymes. In conclusion, in comparing the proteolyses of various foods, it is important to use various enzyme/substrate ratios.