Influência da contagem de células somáticas e microrganismos psicrotróficos na gelificação e sedimentação do leite UAT

Abstract

The objective of this work was to verify the influence that the count of somatic cells and psychrotrophic microorganisms have in the gelling and sedimentation of whole UHT milk. The samples assessed came from six processings of UHT whole milk. In the three processings, three levels of somatic cells present in the unprocessed milk were selected: high (higher than 700,000 cells/ mL), medium (between 400,000 and 700,000 cells/mL) and low (lower than 400,000 cells/mL). In the three other processings, three levels of psychrotrophic microorganisms present in the unprocessed milk were selected: high (higher than 3 x10á), medium (between 1 x 10á and 3 x 10á) and low ( lower than 1 x 10á). Samples of unprocessed milk and UHT milk with 30, 60, 90 and 120 days of shelflife between 25 - 30 degrees centigrade. The physical-chemical analyzes of unprocessed milk with different levels of somatic cells and psychrotrophic microorganisms did not reveal significant differences (P > 0.05). A increase of mass of sediments was found during the time that the UHT milk was on the shelf. The somatic cell count led to a greater sedimentation. The proportions of proteins decreased with the increase of sedimentation. The pH of the UHT milk in ethanol presented an initial increase followed by a progressive decrease, resulting in a lower alcoholic stability at the end of the ´shelf time´. The viscosity of UHT milk increased during the ´shelf time´, revealing a tendency to gelling. Thus, according to the results obtained, it was concluded that the count of somatic cells in the unprocessed milk was determinant to a higher of sediment in UHT milk. It was also concluded that the high counts of somatic cells and the psychrotrophic microorganisms in the unprocessed milk influenced the increase of the UHT milk gelling.