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Thermosensibilités d'enzymes (lactoperoxydase, gamma-glutamyl transpeptidase) et structures protéiques en spectroscopie IRTF : utilisation comme indicateurs de traitements thermiques du lait

Abstract : Two protocols of quantification of enzymatic activity in milk were finalized. The first was the measurement of lactoperoxydase (LPO) activity. The second was the measurement of[gamma]-glutamyl transpeptidase ([gamma]-GT) activity. They incorporated a clarification step of the reaction mixture that allowed a direct spectrophotometric measurement from which an appreciable time-saving. Milk heated in the range of 50 to 80°C showed that the thermo-sensitivity of LPO and [gamma]-GT renders these enzymes useful to estimate the efficiency or the severity of pasteurization. Results obtained with these protocols on various milks presented a good correlation (R[exponent 2] >= 0,97) with those obtained with reference protocols. These new protocols could be applied on cheese too. Fourier transform infrared spectroscopy was selected for the study of changes in protein spatial conformation. When heating milk at 80°C, protein b-sheet and a helix proportions decrease slightly. Proportion of turns and random coils increase. Turn proportion could serve as thermal indicator. These study will have to be confirmed by using a sufficient number of milks for which thermal historic is known.
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Theses
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http://docnum.univ-lorraine.fr/prive/SCD_T_2002_0034_BLEL.pdf
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https://hal.univ-lorraine.fr/tel-01746512
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Submitted on : Thursday, March 29, 2018 - 10:39:25 AM
Last modification on : Wednesday, October 21, 2020 - 3:48:35 PM

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Mustapha Blel. Thermosensibilités d'enzymes (lactoperoxydase, gamma-glutamyl transpeptidase) et structures protéiques en spectroscopie IRTF : utilisation comme indicateurs de traitements thermiques du lait. Biochimie [q-bio.BM]. Université Henri Poincaré - Nancy 1, 2002. Français. ⟨NNT : 2002NAN10034⟩. ⟨tel-01746512⟩

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