Isolation and characterisation of a heat-resistant peptidase from Pseudomonas panacis withstanding general UHT processes

A secreted peptidase from Pseudomonas panacis was identified and purified. Genome sequencing of the producer strain allowed identification of the peptidase as AprA based on a comparison to peptide sequences of mass spectra obtained from the purified enzyme. The amino acid sequence of the 49.4 kDa peptidase was 98% similar to the metallopeptidase AprX from a Pseudomonas fluorescens strain. The peptidase showed maximum activity at pH 8 and 40 °C and withstood general ultra-high temperature (UHT) processing (138 °C for 18 s) in skim milk, with 88.0 ± 7.7% of the initial enzyme activity remaining after heating. The peptidase showed considerable enzyme activity under storage conditions of UHT milk. The potential for spoilage of milk might during storage was verified by adding very low enzyme activities to UHT-treated milk. The addition of 1 pkat mL−1 peptidase activity resulted in a destabilisation of the milk during four weeks storage.