Sedimentation, proteolytic activity and proteolysis of whole UHT milk during storage

The UHT milk destabilization during storage may be assigned, among other factors, to the activity of endogenous and, or bacterial proteases. This technological problem is a major obstacle in the dairy chain. The aim of this study was to evaluate the microbiological quality of raw milk and its effect on the formation of sediment, degree of proteolysis and proteolytic activity of whole UHT during storage. Mean counts of mesophilic bacteria, psychrotrophic, psychrotrophic proteolytic and Pseudomonas spp. from samples of raw milk were respectively 5.5 x 10(6) CFU/mL, 3.0 x 10(6) CFU/mL, 8.0 x 10(5) CFU/mL and 1.1 x 10(6) CFU/mL. The UHT treatment has reduced 93.2% of proteolytic activity detected comparing to the proteolytic activity of raw milk. The increase in sediment mass, degree of proteolysis and proteolytic activity of whole UHT milk has been detected during storage. All UHT milk samples have presented low count of mesophilic bacteria and remained thermally stable without evidence of gelation. Considering the residual activity of proteases in UHT milk and its relevance to sedimentation, proteolytic activity and proteolysis, the use of raw milk with low levels of proteolytic psychrotrophic bacteria hould be considered to prevent technological problems as sedimentation and gelation, which reduce significantly product acceptance by consumers besides causing industrial losses.