ISBN 9783843957342

978-3-8439-5734-2, Reihe Biotechnologie

Veronika Volk
Characterization, detection and application of heat-stable Pseudomonas peptidases found in milk

290 Seiten, Dissertation Universität Hohenheim Stuttgart-Hohenheim (2025), Softcover, A5

Zusammenfassung / Abstract

Quality defects in milk products during their shelf-life, such as phase separation or the development of bitter flavors, pose well-known challenges to the dairy industry. These changes during shelf-life are caused by the hydrolysis of milk proteins catalyzed by heat-stable endopeptidases. Heat-stable endopeptidases are secreted in raw milk during cold storage for several days prior to UHT treatment, where psychrotolerant microorganisms, such as Pseudomonas sp., can dominate the microbiota of raw milk. Endopeptidases involved in the development of quality defects during shelf-life are especially attributed to the class of AprX (EC 3.4.24.40), heat-stable alkaline metallopeptidases. AprX are not fully inactivated by UHT treatment, leaving residual activity in the milk product which leads to destabilization already at activity levels below 1 pkat/mL. Sensitive detection of these activity levels is challenging for quality control laboratories in dairy plants.

The research reported in this thesis aimed to improve the understanding of AprX characteristics, which should be used to develop sensitive methods for the detection of AprX in milk matrices. Two approaches were followed: (1) based on antigen-antibody interactions and (2) based on substrate selectivity using chromogenic substrates.

Enzymatic hydrolysis is not only known for negative impacts such as milk destabilization in food products but is also described for positive impact on food proteins. Thus, AprX hydrolysis was investigated for its potential to enhance the emulsifying properties of food proteins from milk, plant, and insect origin.