Abstract
Milk is a nutritionally important food, particularly due to its milk protein content. The representation and degradation of individual protein fractions in raw cow’s milk were monitored using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), with a focus on the presence of undesirable milk microbiota and somatic cell count (SCC). Raw cow’s milk samples (n = 240) were collected from three farms in accordance with the principles of the international standard STN EN ISO 707 during the autumn 2022/winter 2022/spring 2023/summer 2023. After cultivating microorganisms (ISO/TS 11059), 73 isolates of Pseudomonas spp. were identified using the polymerase chain reaction (PCR). Subsequently, qualitative parameters, including somatic cell count, protein content, and protein profile, were analyzed. The results showed statistically significant differences (p < 0.001) in relation to seasonal changes. The findings indicate significant interactions between the presence of Pseudomonas spp., somatic cell count, seasonality, and the content and composition of milk proteins (p < 0.001). The presence of Pseudomonas spp. and a high somatic cell count contributed to a decrease in the αs2-casein, αs1-casein, and ß-casein fractions, accompanied by an increase in serum proteins β-lactoglobulin and α-lactalbumin (p < 0.001). The negative impact of these changes in protein composition affects the further processing of milk in the dairy industry, particularly in cheese production. The aim of this work was to determine the level of the protein fractions degradation caused by the presence of undesirable dairy Pseudomonas spp. using proteomic methods, considering SCC.