In this work, we studied the protease activity of Pseudomonas spp. bacterial isolates and the heat resistance of their proteases in different media. Proteolytic activity was determined by the azocasein method after incubation of isolates in tryptic soy broth, chicken meat homogenate and fresh chicken meat. Residual proteolytic activity was determined after 5 and 30 minutes of heat treatment at different temperatures. Isolates differed in proteolytic activity and heat resistance of their proteases, which depended on the growth medium and the time and temperature of incubation during growth and heat treatment. High cell density did not always indicate the presence of protease activity. Isolate CC135 was also proteolytically active, even though the presence of the aprX-lipA2 operon was not confirmed for it. In liquid media, proteases retained part of their activity after heat treatment, with the residual activity not only decreasing linearly with increasing temperature, but rather showing the phenomenon of inactivation at lower temperatures. Protease activity was detected in fresh chicken meat after 7 days of incubation, but was no longer detected after heat treatment. The active proteases were estimated by zymogram to be 50 kDa. We have shown that based on the results of protease activity and heat resistance of Pseudomonas proteases, obtained in liquid laboratory media, we cannot directly conclude about their behavior in solid substrates, such as fresh chicken meat, since their activity and response to heat treatment vary depending on the matrix.
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