Different methods and times of milk conservation: physical-chemical composition and microbiological quality

Résumé

The objective of this study was to verify methods of preservation of raw milk samples for physical-chemical analysis and bacterial count patterns. In Experiment 1, the experimental design was a factorial arrangement with three preservatives × two temperatures × five storage times. At seven days of storage, the samples with no preservative had higher total bacterial counts (TBC). However, the fat content increased in the refrigerated samples. The levels of protein, lactose and defatted solids were influenced by the analysed variables and by the interaction between them. Milk pH was influenced by the type of preservative and the duration of storage. Experiment 2 involved an evaluation of the influence of initial TBC, temperature and storage days. The factorial arrangement involved two TBCs × two temperatures × five storage times. The TBC, pH and total solid content of milk were influenced by the analysed variables. There was a quadratic pattern for TBC over storage days. With regard to fat, there was an effect of the initial TBC and storage temperature. Protein and lactose increased, with subsequent stabilisation. Samples with high initial TBC presented higher total solids levels. There was an effect of the interaction between TBC and temperature, and between temperature and storage days. For TBC analysis, the use of azidiol as a preservative is dependent on the use of refrigeration during storage. For physical-chemical analysis, the use of bronopol is indicated.