Highly perishable foods, due to their rich nutritional composition, high water activity and neutral pH, allow the rapid growth of microorganisms, leading to changes in the texture, colour, taste and smell of the food, and thus to its inability to be used. In this master thesis, the microbiological spoilage of pork and poultry meat and fish was addressed, focusing on bacteria of the genus Pseudomonas as key spoilage agents. Bacteria of the genus Pseudomonas cause the degradation of muscle proteins, the formation of volatile nitrogen compounds and sensory alterations in foods through the synthesis of extracellular enzymes, called proteases. According to previous studies, we found that the composition of the culture medium, the concentration of protein and ionic components, and the culture conditions (temperature and pH) influence the level of protease activity. The focus of this thesis was on the selection of the optimal medium for the synthesis of extracellular proteases, where the influence of different protein substrates and ionic solutions on their synthesis was investigated. We found that cells synthesised proteases most efficiently in the presence of peptone from casein and in the presence of macro- and microion solutions. We also studied the dynamics of the release of extracellular proteases over a period of nine days at three temperatures (5 °C, 15 °C and 30 °C), with the highest synthesis and cell growth recorded at 15 °C. In addition, we evaluated the protease activity of all 22 Pseudomonas isolates from different types of spoiled meat and found that it varies among the isolates. The results contribute to a better understanding of the mechanisms of spoilage in highly perishable foods and may serve as a basis for the development of effective approaches to extending foods shelf life.
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