Caracterización del sistema proteolítico de Debaryomyces hansenii aislada de embutidos curados.

Résumé

Proteolysis is one of the key factors in the flavour development of dry-cured fermented sausages. On the other hand, Debaryomyces hansenii, is the more abundant yeast specie in fermented sausage, and it has been associated with the proteolytic changes that take place in cured products. However, there are very few biochemical studies related to the characteristics and possible functions of the proteolytic system of D. hansenii. Therefore, the main objective of the present Thesis was to study the proteolytic system of D. hansenii, by means of the purification and characterisation of the most important enzymes as well as the factors affecting to its synthesis. Firstly, the strain D. hansenii CECT 12487 was selected by its highest proteolytic activity. This strain was capable to hydrolyse the muscle sarcoplasmic proteins generating peptides and free amino acids of importance for the taste, and as precursors of aromatic compounds. The inoculation of viable cells or cell extracts allows to modulate qualitative and quantitatively the resulting products. The purification and characterisation studies revealed that the proteolytic system from D. hansenii, it is constituted at least, for two aminopeptidases, a prolyl aminopeptidase (PAP) and an arginyl aminopeptidase (AAP), and two endoproteases, the protease A (PrA) and the protease B (PrB). The characterisation of these enzymes and its possible influence during the curing of meat products it is described in the corresponding sections of the PhD Thesis. The specific proteolytic activities of the studied enzymes, PAP, AAP, PrB and PrA, were increased in poor or complex nitrogen and carbon sources, and at the time, the cellular growth advances toward the stationary phase. The production of cultures or cell extracts of D. hansenii using urea as nitrogen source, as well as long times of harvest, permit to reach maximum levels of total proteolytic activity. And therefore, it could constitute a good alternative for its incorporation to the meat formulation, and to improve the ripening of cured sausages.