Quantitative and qualitative variability of the caseinolytic potential of different strains of Pseudomonas fluorescens: Implications for the stability of casein micelles of UHT milks during their storage

• Published in: Food chemistry 2012-12, Vol.135 (4), p.2593-2603
• Main Authors: Baglinière, François, Tanguy, Gaëlle, Jardin, Julien, Matéos, Aurélie, Briard, Valérie, Rousseau, Florence, Robert, Benoît, Beaucher, Eric, Humbert, Gérard, Dary, Annie, Gaillard, Jean Luc, Amiel, Caroline, Gaucheron, Frédéric
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Casein; Casein micelles; Caseins - chemistry; Caseins - metabolism; Cattle; Chromatography, High Pressure Liquid; Food industries; Food Storage; Fundamental and applied biological sciences. Psychology; Hot Temperature; Life Sciences; Mass Spectrometry; Milk - chemistry; Milk - microbiology; Milk and cheese industries. Ice creams; Protease; Proteolysis; Pseudomonas fluorescens; Pseudomonas fluorescens - metabolism; Species Specificity; Stability; UHT treatment
• ISSN: 0308-8146; 1873-7072
• DOI: 10.1016/j.foodchem.2012.06.099

► Destabilization of UHT milk by Pseudomonas fluorescens is strain dependent. ► All casein molecules were hydrolysed by heat stable enzyme(s) from P. fluorescens. ► Enzymatical hydrolysis of casein induces casein micelle destabilization. Pseudomonas fluorescens grows at low temperature and produces thermo-resistant protease(s) that can destabilize UHT (Ultra High Temperature) milk during its storage. The consequences of contamination of microfiltered milk with 9 strains of P. fluorescens on the stability of the corresponding UHT milk during storage had been investigated in this study. The strains were classified in two groups according to their ability to destabilize UHT milk. For the group of highly destabilizing strains, sedimentations of UHT milks, low values to phosphate test and the presence of aggregates were observed. Zeta potential and hydration of casein micelles decreased, whereas non casein nitrogen (NCN) and non protein nitrogen (NPN) contents increased. The analyses of NCN fraction by liquid chromatography coupled to mass spectrometry indicated that the different casein molecules were hydrolyzed in a similar way for the destabilizing strains suggesting that the same enzyme was implicated. For the group of slightly or not destabilizing strains no visual and biochemical alteration were found. This study showed that destabilization of UHT milk by P. fluorescens was highly variable and strain-dependent.