Mesophilic microorganisms in UHT milk

Abstract

Milk treated by Ultra High Temperature - UHT is present in most national diets and takes a fundamental role in human nutrition. Mesophilic microorganisms stand out as the main product quality indicators. Thus, the objective of this paper was to detect, quantify and evaluate the Gram morphology of mesophilic bacteria isolated from three different brands of UHT milks submitted or not to incubation. 90 samples of UHT milk (A, B, and C) were obtained from supermarkets in the region of Curitiba, PR. Half of the samples were subjected to incubation (36 °C/7 days) before analysis and the other half was evaluated within 2 hours after acquisition for Standard Plate Count (SPC), Gram staining, and lactofermentation test. 30% of the analyzed samples contained more than 100 CFU/mL of mesophilic aerobes, with 20% and 29% of the samples incubated or not, respectively. The A mark had the highest counts, followed by the B and C marks. The results after incubation also revealed higher counts in the A mark samples. The Gram stain results revealed the predominance of Gram-positive cocci in all samples, incubated or not. In the lactofermentation test, coagulation was observed after 48 h and 96 h of incubation in at least one sample without previous incubation and in samples with incubation for seven days of brands A and B (batches 1 and 3). Therefore, it was identified the possibility of having samples and brands of UHT milk available on the market that go beyond the limits established by legislation concerning the counting of mesophilic microorganisms.