Resumo

Proteolytic enzymes are associated with bitterness in milk because of hydrolysis of the peptide bonds, whereas lipolytic enzymes hydrolyze milk fats and are associated with rancidity. Such enzymes are not inactivated by pasteurization and sterilization treatments because of their thermoresistance. Proteolytic digestion of milk can lead to clotting and gelation of milk casein. One metalloprotease called AprX which belongs to the serralysin family, has been characterized in Pseudomones fluorescens with high potential for milk protein degradation. The aim of this study was to evaluate the caseinolytic activity of microorganisms isolated from a dairy industry-plant. Fifteen microorganisms isolated by culturing on agar base Pseudomonas media. Among those isolates, seven were shown to have the aprX gene sequence in their genome. The colonies were identified by DNA sequencing as Pseudomonas corrugate, P. cedrina sub sp. Fulgida,Stenotrophomonas maltophilia, P. taetrolens, P. japônica and P. fluorescens. Cells form those were harvested after 72 h of growth in a complex medium (CM) at 30ºC and the concentration of protein was measured of supernatant obtaining 1,5 mg/mL; 1,46 mg/mL; 1,9 mg/mL; 0,7 mg/mL; 2,0 mg/mL; 0,8 mg/mL and 2,3 mg/mL; respectively. The caseinolytic activity of each one of those strains was determined at the culture media using azocasein as a substrate . The proteolytic activity in the P.corrugata, P. cedrina sub sp. fulgida and S. maltophilia were of 17,4%, 19,6% e 25,2% higher than the proteolytic activity of the reference strain P. fluorescens (ATCC 13525). By the other hand, the P. taetrolens, P. japônica and P. fluorescens showed a reduced proteolytic activity reaching 90,8%, 82,3% e 72,1%, respectively, of the reference strain. This study revealed a great heterogeneity among the contaminant strains within Pseudomonas genera found in a dairy plant that can represent potential spoilage able to degrade proteins in dairy products.