PHYSICAL-CHEMICAL AND MICROBIOLOGICAL QUALITY OF BOVINE MILK IN DIFFERENT PRODUCTION SYSTEMS AND SEASONS

Abstract

The objective of this work was to evaluate the effect of the interaction between production systems and seasons on physical-chemical and microbiological qualities of bovine milk. Three farms were assessed monthly, along the seasons, for four specialization levels of the production systems: highly specialized, specialized, partially specialized, and non-specialized. In terms of milk quality, the levels of fat, protein, total solids, somatic cell count, total bacterial count, titratable acidity in degrees Dornic, density, cryoscopic index, alizarol stability, potential of hydrogen (pH) and methylene blue reduction test. In addition, due to their importance for the industrial yield of protein-based dairy products, total milk protein fractionation was performed in protein equivalent of non-protein nitrogen, true protein and casein.The milk Dornic acidity was higher in spring and winter, while the highest somatic cell count values were in the summer. Total and true protein levels were lower during the summer and total solids increased in the autumn. With the decrease in the levels of specialization of farms, there was an increase in total bacterial count and decrease in non-protein nitrogen. The density presented an inverse behavior to that of the fat while the hydrogen potential (pH) was expressed in a way antagonistic to the acidity. In the multivariate analysis of the data it was possible to identify the combinations between production strata and stations that presented the best milk protein quality. In this sense, all the arrangements of production systems with autumn, winter highly specialized, summer partially specialized, spring specialized had positive protein quality, being highlighted by the smaller of somatic cells counts in the spring partially specialized combination. 
Keywords: multivariate analysis, principal components analysis, milk quality, typology, milk production units.