title: Extracellular prolyl endoprotease from Aspergillus niger and its use in the debittering of protein hydrolysates.
abstract: The observation that the bitterest peptides from casein hydrolysates contain several proline residues led us to hypothesize that a proline-specific protease would be instrumental in debittering such peptides. To identify the desired proline-specific activity, a microbiological screening was carried out in which the chromogenic peptide benzyloxycarbonyl-glycine-proline-p-nitroanilide (Z-Gly-Pro-pNA) was used as the substrate. An Aspergillus niger (A. niger) strain was identified that produces an extracellular proline-specific protease with an acidic pH optimum. On the basis of sequence similarities, we conclude that the A. niger-derived enzyme probably belongs to the S28 family of clan SC of serine proteases rather than the S9 family to which prolyl oligopeptidases belong. Incubating the overexpressed and purified enzyme with bitter casein hydrolysates showed a major debittering effect. Reversed phase HPLC analysis revealed that this debittering effect is accompanied by a significant reduction of the number of hydrophobic peptides present.
authors.affiliation: DSM Food Specialties, Post Office Box 1, 2600 MA Delft, The Netherlands. luppo.edens@dsm.com
authors.forename: Luppo
authors.initials: L
authors.lastname: Edens
authors.forename: Peter
authors.initials: P
authors.lastname: Dekker
authors.forename: Rob
authors.initials: R
authors.lastname: van der Hoeven
authors.forename: Flip
authors.initials: F
authors.lastname: Deen
authors.forename: André
authors.initials: A
authors.lastname: de Roos
authors.forename: René
authors.initials: R
authors.lastname: Floris
mesh_terms: D000595:Amino Acid Sequence; D001234:Aspergillus niger / Q000201:enzymology* / Q000235:genetics; D002364:Caseins / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D015870:Gene Expression; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D000085822:Prolyl Oligopeptidases; D011492:Protein Hydrolysates / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D012697:Serine Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D013379:Substrate Specificity; D013649:Taste
chemical_list: D002364:Caseins; D011492:Protein Hydrolysates; D015842:Serine Proteinase Inhibitors; D012697:Serine Endopeptidases; D000085822:Prolyl Oligopeptidases