Destabilization of UHT milk by protease AprX from Pseudomonas fluorescens and plasmin

Chunyue Zhang, Etske Bijl, Kasper Hettinga*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

42 Citations (Scopus)


Destabilization of UHT milk during its shelf life is mainly promoted by the residual proteolytic activity attributed to the psychrotrophic bacterial proteases and native milk proteases. In this study, we built skim UHT milk-based model systems to which either the major bacterial protease (AprX from Pseudomonas fluorescens), or the major native milk protease (plasmin) was added, to allow a direct comparison between the destabilization of skim UHT milk by both categories of enzymes. The physical and chemical properties were studied during 6 weeks. Our results showed AprX induced compact gels when almost all the κ-casein was hydrolyzed and the degree of hydrolysis (DH) exceeded 1.3%. Plasmin induced soft gels when around 60% of both β- and αs1-casein were hydrolyzed and the DH reached 2.1%. The knowledge gained from this study may be used for developing diagnostic tests for determining the protease responsible for UHT milk destabilisation.

Original languageEnglish
Pages (from-to)127-134
Number of pages8
JournalFood Chemistry
Publication statusPublished - 15 Oct 2018


  • AprX
  • Destabilization
  • Gelation
  • Hydrolysis
  • Plasmin
  • Shelf life
  • UHT milk


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