Caracterização de variáveis relacionadas com a estabilidade do leite bovino.

Abstract

One of the factors that compromises the milk quality is the loss of stability in the face of alcohol. The milk instability impair the industry, in the production of dairy derivatives, since milk precipitates when subjected to high temperatures during thermal processing. The objective of the research was to analyze the milk stability from producers in the State of Paraná, through the alcohol test under six concentrations and to relate it to the factors that may interfere with the stability. Milk samples were collected from the producers' cooling tanks, being collected twice in the summer and twice in the winter, generating 425 and 389 samples, respectively, totaling 814 samples. The properties were classified according to the level of intensification of the production systems: pasture with supplementation (PS) and confinement (CO). In the laboratory, the samples were submitted to alcohol test, titratable acidity and ionic calcium concentration (Cai), chemical composition, somatic cell count (SCC) and standard plate count (SPC). Descriptive and correlation analyzes were performed. In the analysis of variance the season of the year (winter or summer) and the production system (PS or CO) were evaluated. Logistic regression analyzes were calculated to determine the probability of occurrence of unstable non-acid milk (UNAM) at alcohol concentrations of 72 and 78 °GL. In the multiple linear regression analysis, milk stability was considered as the dependent variable. Milk stability was higher in winter and presented lower levels of Cai compared to summer. Regarding the production system, it was found that cows kept in confinement produced milk with greater stability and lactose content compared to cows raised under grazing. Stability was negatively correlated with Cai and positively correlated with lactose content. The titratable acidity showed a positive correlation with stability, possibly due to the high natural acidity observed. The incidence of UNAM considering alcohol at 72°GL was 12.16% and in alcohol at 78°GL it was 34.64%. In the logistic regression of risk for UNAM72, only the variables Cai and lactose were determinants, while in Unam78 the determinant variables were Cai, titratable acidity, lactose and milk urea nitrogen. In the multiple linear regression, lactose (partial r2 = 0.13) and Cai (partial r2 = 0.06) were the variables that showed a significant linear increase for milk stability, however, the model explains only 26.6 % (total r2 = 0.266) of the total variation. Under the production conditions of dairy cattle in Paraná, the occurrence of UNAM72 was low, more frequently in the summer and in the pasture production system with supplementation. The determining and common variables for UNAM72 and UNAM78 were Cai and lactose concentrations. Therefore, it is proven that the occurrence of UNAM in the State of Paraná was low and the causes were multifactorial.