Lipoproteolytic deteriorating potential and aprX gene of Pseudomonas spp. in raw goat milk.

This Research Communication describes the frequency of occurrence of P. fluorescens, P. putida and P. aeruginosa 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 aprX 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 Pseudomonas CFC agar base (25°C for 48 h). The presence of P. fluorescens, P. putida, P. aeruginosa and aprX 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 Pseudomonas spp. were obtained. At both temperatures, P. fluorescens 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 P. putida were lipoproteolytic, with a predominance of protease synthesis. Strains of P. aeruginosa (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 P. aeruginosa, but not its spoilage potential. The presence of the aprX 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 Pseudomonas 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.