An in vitro enzymic method was used to study the kinetics of digestion of casein and rapeseed proteins. After a predigestion step with pepsin (EC 3.4.23.1), the protein substrates were submitted to a 24 h hydrolysis either with pancreatin or pancreatic juices of pigs adapted either to casein or rapeseed diets and whose enzyme activities were different. After 3, 6 and 24 h of in vitro digestion, dialysates were collected and analysed for content of nitrogen, amino acids and low-molecular-weight peptides. For a long-term hydrolysis (24 h), overall digestibility of both substrates was not affected by the composition of pancreatic enzyme mixtures. However, at the beginning of hydrolysis a significant effect of pancreatic juices was observed, i.e. individual amino acid digestibility was generally higher when casein pancreatic juice was used for hydrolysis and their relative pattern of release was modified. For both substrates the proportion of amino acids released as low-molecular-weight peptides was not affected by the enzyme mixture used and made up about two-thirds of the total digested material. It is concluded that exocrine pancreatic adaptation to protein sources does not affect the total capacity of protein digestion. However, the changes in initial kinetics of release of amino acids are more dependent on the nature of the protein tested than on the composition of pancreatic enzyme mixtures.

The effect of dietary protein on enzyme activity of pancreatic juice was studied in ten growing, castrated, Large White male pigs. Animals, fitted with permanent cannulas in the pancreatic duct and in the duodenum, were divided into two groups receiving either casein or rapeseed concentrate as a protein source. After a 15 d adaptation period to the experimental diet, the volume of pancreatic secretion was significantly higher, whereas the protein concentration was lower in the casein group compared with the rapeseed group. No statistical difference was observed in the daily protein output between groups. Total secreted activities of carboxypeptidase A (EC 3.4.17.1), and elastase (EC 3.4.21.36) were higher in the casein group during the nocturnal period, whereas total activities of trypsin (EC 3.4.21.4), chymotrypsin (EC 3.4.21.1), carboxypeptidase B (EC 3.4.17.2) and amylase (EC 3.2.1.1) in pancreatic secretions during the post-prandial periods were increased by the ingestion of the rapeseed diet. It is concluded that the pancreatic enzyme secretion is sensitive to the nature of the protein ingested.