Marqueurs biologiques de la qualité de la viande

Abstract

The tenderizing of meat is an apoptotic phenomenon with post-mortem proteolytic degradation involving caspases. The dynamic control of caspases is modulated by changes in the physicochemical conditions of the cell and by the inhibitors present within the cell. Inhibitors of serine proteases or serpins are then the best biomarkers of tenderness (Zamora et al., 1996 ; Zamora, 1997 ; Ouali, 1999 ; Zamora et al., 2005). Caspases are strongly inhibited by these serpins (Herrera-Mendez et al., 2009). These constitute a point of control of apoptosis. The main objective of our thesis was to demonstrate the ubiquity of apoptosis in different beef species and in freshwater fish by markers: 1- Degradation of actin protein target of caspases; 2-Reversal of the polarity of the cell membrane 3- Alteration of mitochondria with release of cytochrome C. A synthesis on bovine serpines and their role in meat-softening has become a secondary objective. For the demonstration of the ubiquity of apoptosis, we studied: 1 - the inversion of the polarity of the cell membrane by immunohistochemistry, 2 - the mitochondrial alteration with release of cytochrome c and followed up by western blot; 3-degradation of actin and follow-up of fragments by Western Blot. Our synthesis on serpines led us to reproduce the different techniques described in studies on bovine muscle (Herrera Mendez, 2006) including chromatography using the Fast Protein Liquid Chromatography System (FPLC) supplemented by observations of tissue sections with a fluorescence microscope. Our results make it possible to confirm that the apoptotic cell uses a preformed protein mechanism in the cell, whose implementation is triggered as soon as the apoptosis signal is perceived. This signal would be emitted by a reversal of the polarity of the membrane through the translocation of phospholipids located on the inner face of the plasma membrane (phosphatidylserine) to the outer face of this membrane. The rate of cytochrome c increases over time post mortem suggesting that mitochondria are probably altered by the intrinsic mitochondrial pathway. The appearance of various fragments of actin degradation of 30 KDa and less in the different species studied makes it possible to suggest a variability of the enzyme / inhibitor ratio according to the species and the efficiency of their proteolytic systems. Through our results, we confirm the implementation of the apoptotic process in muscle cells, from the first moments post mortem.The first alterations are probably related to the action of caspases. Concerning the bovine serpines and their role in the tenderizing of the meat, the results confirm their intervention in the strong inhibition of the initiating and executing caspases. The serpins can then be considered as complementary levels of control of the apoptotic process and therefore potential markers of the tenderness of the meat.