Lipoproteolytic deteriorating potential and <i>apr</i>X gene of <i>Pseudomonas</i> spp. in raw goat milk

This Research Communication describes the frequency of occurrence of <i>P. fluorescens</i>, <i>P. putida</i> and <i>P. aeruginosa</i> in raw goat milk stored at 4 and 9°C, to evaluate the spoilage potential and capacity of these species and the presence of the <i>apr</i>X gene, responsible for the synthesis of metalloprotease aprX. Samples of raw goat milk stored at 4 and 9°C for 72 h were plated on <i>Pseudomonas</i> CFC agar base (25°C for 48 h). The presence of <i>P. fluorescens</i>, <i>P. putida</i>, <i>P. aeruginosa</i> and <i>apr</i>X gene were confirmed by polymerase chain reaction. The isolates were evaluated for their proteolytic and lipolytic spoilage capacity and potential using milk agar (10%) and tributyrin agar base (1%), respectively (21°C for 72 h). A total of 184 strains of <i>Pseudomonas</i> spp. were obtained. At both temperatures, <i>P. fluorescens</i> was the most frequent, mostly proteolytic, and the only one to express high proteolytic and lipolytic potentials. Regardless of the temperature, all isolated strains of <i>P. putida</i> were lipoproteolytic, with a predominance of protease synthesis. Strains of <i>P. aeruginosa</i> (4,3%) were isolated occasionally (4.3% of total isolates) but only at 4°C, and 75% of these were lipoproteolytic. The storage temperature of raw goat milk influenced the frequency of <i>P. aeruginosa</i>, but not its spoilage potential. The presence of the <i>apr</i>X gene was verified in most strains isolated from all species at the two temperatures evaluated, although some of these strains did not express proteolytic capacity. Most isolates of <i>Pseudomonas</i> spp. showed lipoproteolytic capacity, which emphasizes the importance of ensuring low initial populations of this genus in raw chilled goat milk when it is used to produce dairy products.