Approaches to Microbial Testing of Dairy Products

Psychrotrophic Pseudomonas bacteria cause microbial spoilage of fresh cheese, manifested as blue pigmentation on its surface. This and other undesirable characteristics reduce the quality and shelf-life of cheese. This comprehensive microbiological research featured dairy products with signs of spoilage: raw milk, intermediate products of milk processing, and cheese. We isolated bacteria of the genus Pseudomonas from various stages of pasteurized milk production using different approaches to monitoring a dairy plant. On storage day 28, cheese with blue curd grains still complied with the microbiological standards (TR CU 033/2013), but failed to pass the sensory evaluation. Pseudomonas fluorescens, which were found responsible for the blue pigment, entered the dairy plant with raw milk, whose contamination level ranged from 4,0×103 to 1,0×105 CFU/g. The raw cream with 10% fat produced at the same dairy plant had 4,0×106 CFU/g, which means that pasteurization reduced the bacterial contamination but provided no protection. Moreover, eight out of fourteen washing samples from the technological equipment contained thirteen pseudomonad species. Of these, nine belonged to Ps. . Bacteria of the genus Pseudomonas proved to be a major microbial spoilage threat to dairy products. The article also introduces hazardous factors, objects of technological control, control assessment indicators, and measures against blue coloration of curd grain caused by Ps. fluorescens.