Microwave digestion of proteins

The time needed for a conventional acidic digestion of peptide bonds in proteins with 6 N HCl was reduced from 18-24 h to 2 h when microwaves were applied. The rate-determining step of the splitting of the peptide bonds depends on the amino acid composition of the proteins. Myoglobin, lysozyme and bovine serum albumin were tested as pure model proteins. The amino acid contents determined after ion-exchange HPLC and postcolumn derivatisation with ninhydrin correlated well with values obtained on the basis of known amino acid sequences. Tryptophan, methionine as well as cysteine/cystine were partly or completely destroyed under the hydrolysis conditions applied. Almost 95% of the thermolabile amino acids (based on theoretical values) could be recovered. The conditions were further applied for the hydrolysis of food proteins like casein, commercially available whey proteins as well as pea proteins, and a comparison with the results of the conventional hydrolysis (24 h) was made.