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Lipolytic and proteolytic activity of Pseudomonas spp. isolated during milking and storage of refrigerated raw milk

Abstract

The aim of this study was to verify the presence of lipolytic and proteolytic Pseudomonas spp. during milking and storage of refrigerated raw milk. We also intended to compare samples collected during rainy and dry seasons, from farms with manual and mechanical milking systems. For this, samples of milkers' hands, cows' teats, water, expansion tanks, equipment and utensils used during milking were analyzed regarding Pseudomonas spp. count. Positive samples were tested for the production of lipolytic and proteolytic enzymes. Microorganisms of the genus Pseudomonas were isolated from all sampling points. There was a higher isolation rate of the bacterium in the rainy season except for six sampling points with all of these associated with mechanical milking systems. Pseudomonas spp. exhibiting lipolytic activity were found to be predominant during the dry season, since no activity was detected during the rainy season in 26 of the 29 sampling sites. Highest number of lipolytic Pseudomonas isolates were obtained from water. Presence of lipase-producing Pseudomonas spp. was verified in 7% and 36% of the samples collected from farms with manual and mechanical milking, respectively. When analyzing raw milk collected from expansion tanks immediately (0 h) and 24 h after milking, we observed that for dairy properties with manual milking process, 10% of the Pseudomonas isolates were positive for lipolytic activity. The percentage increased to 12% 48 h after milking. Mean averages were 32%, 33% and 39% immediately after, 24 h and 48 h after milking, respectively, for farms with mechanical milking. All sampling points showed the presence of proteolytic strains of Pseudomonas. The highest proteolytic activity was found during the rainy season, except for the samples collected from milkers' hands before milking, buckets and teat cups inner surface after milking and from the water in dairy farms with mechanical milking system. Of these samples, 72%, 56% and 50%, respectively, were positive for proteolysis during the dry season. For the water samples, it was observed statistical difference between mechanical (50%) and manual (7%) milking systems in the percentage of proteolytic activity.No production of proteolytic enzyme was detected in the samples from milkers' hands taken after milking and there was no statistically significant difference among manual (19.91%) and mechanical (47.85%) milking. During the rainy months, no proteolysis was detected in the samples taken from cows' teats after the pre dipping. It is evident, therefore, that preventive measures capable of minimizing the contamination with Pseudomonas spp. during milking and storage of refrigerated raw milk are needed, regardless of season. (AU)

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