The Microorganism Contamination Affect the Physical and Chemical Composition of Milk



The changes that occurred in the Brazilian dairy industry since 1990 began the advances in milk production observed in recent years and the greatest reflection of this transformation was the implementation of the new legislations. The somatic cell count (SCC) and total bacterial count (TBC) in milk are among the most discussed factors due to their importance in Brazil and related to losses at farms and industry. Studies evaluating the effect of TBC on the milk components are scarce and generally assess the effects of confounding between SCC and TBC. The objective of this study was to evaluate the milk from Zebu contamination by somatic cell count (SCC) and total bacterial count (TBC), isolated.

Material, Methods and Results

The samples were collected monthly from 180 farms in the Territory of Identity of the Middle Southwest Bahia. The samples were collected in the farms after manual milking and before cooling in sanitized plastic containers with a volume of 1 L. The contents of crude protein, fat, and lactose, SCC and TBC were determined electronically. Were formed 4 classes of the SCC and TBC. The up limit of the SCC was200,000 cells/ml were selected in order to evaluate only the effect of TBC on milk components, being classified in the same categories mentioned above. As the SCC increased, the contents of fat, crude protein, and total solids increased, an inverse behavior in relation to the content of lactose, which decreased. The TBC presented an inverse behavior, and, as it increased, the contents of fat, protein, and total solids decreased, however with no significant effect between the first and the last class.


The increase in the content of crude protein in milk with high SCC is caused by the increase in serum proteins, especially the immuno-globulins; however, the fraction which is the most important for the dairy industry, the casein, decreases. The TBC results indicate that the country will face difficulty to produce milk and derivatives for export.Still, the TBC indicate that there are effects on the macrocomponents of milk, without a very clear behavior. However, the most adverse effects are observed in the degradation process of these. Two processes interact to decrease the content of lactose in the milk, i) mastitis, which causes reduced production in the mammary gland, and; ii) increased consumption by contaminant microbiota, with the increase of that population. The action of the contaminant microbiota on the macrocomponents of milk does not make the adverse effects very clear. The analytical method used in this study determines the protein fraction as a whole, as well as the lipid fraction. However, the protein fraction is divided in: i) casein (CN): α-s1-CN and α-s2-CN; β-CN, γ-CN; ii) serum protein: α-lactalbumin and β-lactoglobulin; iii) nonprotein nitrogen. Among these, casein is the most important for the dairy industry, and the SCC exerts negative effect on it. The proteolytic action of the enzymes produced by the natural microbiota of milk exists; however, with the contamination of the milk (mastitis, or microbial contamination after milking), this exogenous flora increases this proteolysis.In the lipid fraction in milk, there are: i) phospholipids; ii) cholesterol; iii) triacylglycerols; iv) diacylglycerols; v) free fatty acids; vi) monoacylglycerols; vii) free cholesterol; and others. In addition to evaluating the effects on the content of fat, it is necessary to know the effect of SCC and TBC on the lipid fraction.As related, both (SCC and TBC) are the principal factors related to milk quality, especially, TBC.


The somatic cell count and the total bacterial count negatively affect the physical and chemical composition of milk from zebu animals. Few studies were found in the literature that evaluated the effects of contamination of milk from zebu cows, which demonstrates the importance of this study.

Keywords cheese quality, dairy inefficiency, mastitis, milk contamination, zebu.

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