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Etude de la thermosensibilité du système Plasmine-plasminogène-Activateurs du Plasminogène du lait à l'aide de nouvelles méthodes de dosage : Application à l'étude de la stabilité de produits à base de lait chauffé

Abstract : The purpose of this study was to evaluate the influence of the endogenous plasmin system on stability of infant milk based on heated milk. Improved enzymatic methods were developped to assay plasmin (PLM), plasminogen (PLG) and plasminogen activators (PA) in bovine milk. Those assays were used to monitor the levels of endogenous PLM/PLG/P A in milk samples used at the facility during a whole year. The PA level appeared to be stable, while PLM and PLG levels ranged respectively froID alto 3 and 1 to 2 factor, independently froID the season (winter/summer). Thermal inactivation, at temperature between 60 cC and 140 cC, of native PLM, PLG and PA were studied using the Saille improved enzymatic methods. While measured heat inactivation of kinetic of PLM and PLG were in line with previously reported values, PA were, surprisingly, found to be as heat sensible as PLM and PLG in a milk system containing proteins with free -SR group. Thus, heat inactivation of the who le plasmin system in milk appeared to be directly influenced by the presence of -lactoglobulin. Proteolysis affecting infant milks during storage (at 37 cC or at room temperature), monitored by RPHPLC analysis of peptides present in the soluble fraction, were significantly different froID proteolysis induced with added plasmin. Main peptides generated by those proteolysis were identified by LC-MS/MSMS. The results lead us to conclude that natural proteolysîs observed in commercial products was flot due to the plasmin system. The proteolytic agents responsible for this natural proteolysis were found to be heat resistant, even at 90 CC for 60 minutes. This led us to suspect the presence of proteinases froID endogenous psychrotrophic flora in milk. These results have been used for an optimization of the industrial heat treatments during process.
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http://docnum.univ-lorraine.fr/prive/SCD_T_2002_0054_SAINT_DENIS.pdf
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https://hal.univ-lorraine.fr/tel-01746585
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Submitted on : Thursday, March 29, 2018 - 10:40:46 AM
Last modification on : Wednesday, October 21, 2020 - 3:01:13 PM

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Thierry Saint Denis. Etude de la thermosensibilité du système Plasmine-plasminogène-Activateurs du Plasminogène du lait à l'aide de nouvelles méthodes de dosage : Application à l'étude de la stabilité de produits à base de lait chauffé. Biochimie [q-bio.BM]. Université Henri Poincaré - Nancy 1, 2002. Français. ⟨NNT : 2002NAN10054⟩. ⟨tel-01746585⟩

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