Proteolysis of casein micelles by heat-stable protease secreted by Serratia liquefaciens leads to the destabilisation of UHT milk during its storage
2017
Baglinière, François | Jardin, Julien | Gaucheron, Frederic | de Carvalho, Antonio Fernandes | Vanetti, Maria Cristina Dantas | Universidade Federal de Viçosa = Federal University of Viçosa (UFV) | Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Fundação) = CAPES Foundation [Brasilia] (CAPES) | Science et Technologie du Lait et de l'Oeuf (STLO) ; Institut National de la Recherche Agronomique (INRA)-AGROCAMPUS OUEST | Department of Food Technology ; Pir Mehr Ali Shah Arid Agriculture University = PMAS-Arid Agriculture University Rawalpindi (AAUR) | Department of Microbiology ; S. Bortolo Hospital | CAPES (Coordenaç~ao Aperfeiçoamento Pessoal Nível Superior, Grant number: 61 400437/2014-7) and CNPq (Conselho Nacional de Desenvolvimento Científico, Grant number: 480592/2013-6) for the financial support.
Serratia liquefaciens is a psychrotrophic species, frequently found in raw milk, which secretes Ser2, aheat-resistant protease. Involvement of this species in UHT milk destabilisation was investigated in thepresent study. Microfiltered milk was inoculated independently with strains S. liquefaciens L53 or L64.Then, UHT treatment was performed and stability of the corresponding UHT milk was investigatedduring three months of storage. The residual proteolytic activity of strain L53 led to destabilisation ofUHT milk, with sedimentation and formation of aggregates. Hydrolysis of casein micelles was confirmedby the increase in the content of non-casein nitrogen and the identification of numerous peptides comingfrom the four caseins using mass spectrometry. For strain L64, no visual and biochemical alteration werefound. This study showed that Ser2 resists UHT treatment and could be a cause of UHT milk destabilisation;however, this destabilisation by S. liquefaciens was strain-dependent.
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